Quality IT Computer Tips

Computer Keyboard Shortcuts

2010-09-09T15:57:00.000-04:00

Windows system key combinations

F1: Help
CTRL+ESC: Open Start menu
ALT+TAB: Switch between open programs
ALT+F4: Quit program
SHIFT+DELETE: Delete item permanently
Windows Logo+L: Lock the computer (without using CTRL+ALT+DELETE)

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Windows program key combinations

CTRL+C: Copy
CTRL+X: Cut
CTRL+V: Paste
CTRL+Z: Undo
CTRL+B: Bold
CTRL+U: Underline
CTRL+I: Italic

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Mouse click/keyboard modifier combinations for shell objects

SHIFT+right click: Displays a shortcut menu containing alternative commands
SHIFT+double click: Runs the alternate default command (the second item on the menu)
ALT+double click: Displays properties
SHIFT+DELETE: Deletes an item immediately without placing it in the Recycle Bin

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General keyboard-only commands

F1: Starts Windows Help
F10: Activates menu bar options
SHIFT+F10 Opens a shortcut menu for the selected item (this is the same as right-clicking an object
CTRL+ESC: Opens the Start menu (use the ARROW keys to select an item)
CTRL+ESC or ESC: Selects the Start button (press TAB to select the taskbar, or press SHIFT+F10 for a context menu)
CTRL+SHIFT+ESC: Opens Windows Task Manager
ALT+DOWN ARROW: Opens a drop-down list box
ALT+TAB: Switch to another running program (hold down the ALT key and then press the TAB key to view the task-switching window)
SHIFT: Press and hold down the SHIFT key while you insert a CD-ROM to bypass the automatic-run feature
ALT+SPACE: Displays the main window's System menu (from the System menu, you can restore, move, resize, minimize, maximize, or close the window)
ALT+- (ALT+hyphen): Displays the Multiple Document Interface (MDI) child window's System menu (from the MDI child window's System menu, you can restore, move, resize, minimize, maximize, or close the child window)
CTRL+TAB: Switch to the next child window of a Multiple Document Interface (MDI) program
ALT+underlined letter in menu: Opens the menu
ALT+F4: Closes the current window
CTRL+F4: Closes the current Multiple Document Interface (MDI) window
ALT+F6: Switch between multiple windows in the same program (for example, when the Notepad Find dialog box is displayed, ALT+F6 switches between the Find dialog box and the main Notepad window)

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Shell objects and general folder/Windows Explorer shortcuts

For a selected object:

F2: Rename object
F3: Find all files
CTRL+X: Cut
CTRL+C: Copy
CTRL+V: Paste
SHIFT+DELETE: Delete selection immediately, without moving the item to the Recycle Bin
ALT+ENTER: Open the properties for the selected object

To copy a file

Press and hold down the CTRL key while you drag the file to another folder.

To create a shortcut

Press and hold down CTRL+SHIFT while you drag a file to the desktop or a folder.

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General folder/shortcut control

F4: Selects the Go To A Different Folder box and moves down the entries in the box (if the toolbar is active in Windows Explorer)
F5: Refreshes the current window.
F6: Moves among panes in Windows Explorer
CTRL+G: Opens the Go To Folder tool (in Windows 95 Windows Explorer only)
CTRL+Z: Undo the last command
CTRL+A: Select all the items in the current window
BACKSPACE: Switch to the parent folder
SHIFT+click+Close button: For folders, close the current folder plus all parent folders

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Windows Explorer tree control

Numeric Keypad *: Expands everything under the current selection
Numeric Keypad +: Expands the current selection
Numeric Keypad -: Collapses the current selection.
RIGHT ARROW: Expands the current selection if it is not expanded, otherwise goes to the first child
LEFT ARROW: Collapses the current selection if it is expanded, otherwise goes to the parent

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Properties control

CTRL+TAB/CTRL+SHIFT+TAB: Move through the property tabs

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Accessibility shortcuts

Press SHIFT five times: Toggles StickyKeys on and off
Press down and hold the right SHIFT key for eight seconds: Toggles FilterKeys on and off
Press down and hold the NUM LOCK key for five seconds: Toggles ToggleKeys on and off
Left ALT+left SHIFT+NUM LOCK: Toggles MouseKeys on and off
Left ALT+left SHIFT+PRINT SCREEN: Toggles high contrast on and off

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Microsoft Natural Keyboard keys

Windows Logo: Start menu
Windows Logo+R: Run dialog box
Windows Logo+M: Minimize all
SHIFT+Windows Logo+M: Undo minimize all
Windows Logo+F1: Help
Windows Logo+E: Windows Explorer
Windows Logo+F: Find files or folders
Windows Logo+D: Minimizes all open windows and displays the desktop
CTRL+Windows Logo+F: Find computer
CTRL+Windows Logo+TAB: Moves focus from Start, to the Quick Launch toolbar, to the system tray (use RIGHT ARROW or LEFT ARROW to move focus to items on the Quick Launch toolbar and the system tray)
Windows Logo+TAB: Cycle through taskbar buttons
Windows Logo+Break: System Properties dialog box
Application key: Displays a shortcut menu for the selected item

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Microsoft Natural Keyboard with IntelliType software installed

Windows Logo+L: Log off Windows
Windows Logo+P: Starts Print Manager
Windows Logo+C: Opens Control Panel
Windows Logo+V: Starts Clipboard
Windows Logo+K: Opens Keyboard Properties dialog box
Windows Logo+I: Opens Mouse Properties dialog box
Windows Logo+A: Starts Accessibility Options (if installed)
Windows Logo+SPACEBAR: Displays the list of Microsoft IntelliType shortcut keys
Windows Logo+S: Toggles CAPS LOCK on and off

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Dialog box keyboard commands

TAB: Move to the next control in the dialog box
SHIFT+TAB: Move to the previous control in the dialog box
SPACEBAR: If the current control is a button, this clicks the button. If the current control is a check box, this toggles the check box. If the current control is an option, this selects the option.
ENTER: Equivalent to clicking the selected button (the button with the outline)
ESC: Equivalent to clicking the Cancel button
ALT+underlined letter in dialog box item: Move to the corresponding item

References:
http://support.microsoft.com/kb/126449
Retrival Date:
09/09/10

IPHONE Apps

2010-07-26T08:50:00.000-04:00

Pandora Radio

Tune in.

Choose a favorite song or artist and Pandora
Radio plays the music you want to hear and music
just like it. Discover new artists with similar sounds
and skip over songs you don’t like.

Square

Get paid.

Square is a mobile payment system that enables
you to accept credit card payments from customers
and friends — with no contracts, monthly fees, or
hidden costs. Just plug the free card reader into your
iPhone and start swiping.
View in the App Store
http://www.apple.com/iphone/apps-for-iphone/?cid=wwa-naus-seg-iphone10-015&cp=www-seg-iphone10-apps&sr=sem
07-26-10

How to use a computer

2010-07-26T08:36:00.000-04:00

In computing, a keyboard is an input device, partially modeled after the typewriter keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches. After punch cards and paper tape, interaction via teletype-style keyboards became the main input device for computers.
Despite the development of alternative input devices, such as the mouse (computing mouse), touch sensitive screens, pen devices, character recognition, voice recognition, and improvements in computer speed and memory size, the keyboard remains the most commonly used and most versatile device used for direct (human) input into computers.
A keyboard typically has characters engraved or printed on the keys and each press of a key typically corresponds to a single written symbol. However, to produce some symbols requires pressing and holding several keys simultaneously or in sequence. While most keyboard keys produce letters, numbers or signs (characters), other keys or simultaneous key presses can produce actions or computer commands.
In normal usage, the keyboard is used to type text and numbers into a word processor, text editor or other program. In a modern computer, the interpretation of key presses is generally left to the software. A computer keyboard distinguishes each physical key from every other and reports all key presses to the controlling software. Keyboards are also used for computer gaming, either with regular keyboards or by using keyboards with special gaming features, which can expedite frequently used keystroke combinations. A keyboard is also used to give commands to the operating system of a computer, such as Windows' Control-Alt-Delete combination, which brings up a task window or shuts down the machine.

Laptop-size

Keyboards on laptops and notebook computers usually have a shorter travel distance for the keystroke and a reduced set of keys. They may not have a numerical keypad, and the function keys may be placed in locations that differ from their placement on a standard, full-sized keyboard.

Thumb-sized

Smaller keyboards have been introduced for laptops, PDAs, cellphones or users who have a limited workspace. The size of a standard keyboard is dictated by the practical consideration that the keys must be large enough to be easily pressed by fingers. To reduce the size of the keyboard, the numeric keyboard to the right of the alphabetic keyboard can be removed, or the size of the keys can be reduced, which makes it harder to enter text.
Another way to reduce the size of the keyboard is to reduce the number of keys and use chording keyer, i.e. pressing several keys simultaneously. For example, the GKOS keyboard has been designed for small wireless devices. Other two-handed alternatives more akin to a game controller, such as the AlphaGrip, are also used as a way to input data and text. Another way to reduce the size of a keyboard is to use smaller buttons and pack them closer together. Such keyboards, often called a "thumbboard" (thumbing) are used in some personal digital assistants such as the Palm Treo and BlackBerry and some Ultra-Mobile PCs such as the OQO.

Numeric

Numeric keyboards contain only numbers, mathematical symbols for addition, subtraction, multiplication, and division, a decimal point, and several function keys (e.g. End, Delete, etc.). They are often used to facilitate data entry with smaller keyboard-equipped laptops or with smaller keyboards that do not have a numeric keypad. A laptop does sometimes have a numeric pad, but not all the time. These keys are also known as, collectively, a numeric pad, numeric keys, or a numeric keypad, and it can consist of the following types of keys:

arithmetic operators such as +, -, *, /
numeric digits 0-9
cursor arrow keys
navigation keys such as Home, End, PgUp, PgDown, etc.
Num Lock button, used to enable or disable the numeric pad
enter key

Non-standard or special-use types

Chorded

While other keyboards generally associate one action with each key, chorded keyboards associate actions with combinations of key presses. Since there are many combinations available, chorded keyboards can effectively produce more actions on a board with fewer keys. Court reporters' stenotype machines use chorded keyboards to enable them to enter text much faster by typing a syllable with each stroke instead of one letter at a time. The fastest typists (as of 2007) use a stenograph, a kind of chorded keyboard used by most court reporters and closed-caption reporters. Some chorded keyboards are also made for use in situations where fewer keys are preferable, such as on devices that can be used with only one hand, and on small mobile devices that don't have room for larger keyboards. Chorded keyboards are less desirable in many cases because it usually takes practice and memorization of the combinations to become proficient.

Software

Software keyboards or On-Screen Keyboards often take the form of computer programs that display an image of a keyboard on the screen. Another input device such as a mouse or a touchscreen can be used to each virtual key to enter text. Software keyboards have become very popular in touchscreen enabled cell phones, due to the additional cost and space requirements of other types of hardware keyboards. Microsoft Windows and Mac OS X both include on-screen keyboards that can be controlled with the mouse.

Foldable

Further information: Flexible electronics

A foldable keyboard.

Foldable (also called flexible) keyboards are made of soft plastic or silicone which can be rolled or folded on itself for travel.^[2] When in use, these keyboards can conform to uneven surfaces, and are more resistant to liquids than standard keyboards. These can also be connected to portable devices and smartphones. Some models can be fully immersed in water, making them popular in hospitals and laboratories, as they can be disinfected.

Projection/Laser

Projection keyboards project an image of keys, usually with a laser, onto a flat surface. The device then uses a camera or infrared sensor to "watch" where the user's fingers move, and will count a key as being pressed when it "sees" the user's finger touch the projected image. Projection keyboards can simulate a full size keyboard from a very small projector. Because the "keys' are simply projected images, they cannot be felt when pressed. Users of projected keyboards often experience increased discomfort in their fingertips because of the lack of "give" when typing. A flat, non-reflective surface is also required for the keys to be projected onto. Most projection keyboards are made for use with PDAs due to their small form factor.

Optical keyboard technology

Also known as photo-optical keyboard, light responsive keyboard, Photo-electric keyboard and optical key actuation detection technology.
An optical keyboard technology utilizes light emitting devices and photo sensors to optically detect actuated keys. Most commonly the emitters and sensors are located in the perimeter, mounted on a small PCB. The light is directed from side to side of the keyboard interior and it can only be blocked by the actuated keys. Most optical keyboards require at least 2 beams (most commonly vertical beam and horizontal beam) to determine the actuated key. Some optical keyboards use a special key structure that blocks the light in a certain pattern, allowing only one beam per row of keys (most commonly horizontal beam).
http://en.wikipedia.org/wiki/Keyboard_%28computing%29
07-26-10

Top 100 companies

2010-07-26T08:31:00.000-04:00

3COM Corp.
Activision
Adobe
ADTRAN
Advanced Micro Devices, Inc.
Agilent Technologies, Inc.
Altera Corporation
Amazon.com
Analog
Anixter
Apple Computer Inc
Applied Materials, Inc.
Arrow Electronics Inc
ATI Technologies Systems Corporation
Atmel
Autodesk Inc.
Cadence
Canon
CDW
Cirrus Logic, Inc.
Cisco
Cognizant Technology Solutions
Coherent Corp
Computer Associates International, Inc.
Computer Sciences Corporation
Compuware Corp
Comverse Technology, Inc.
Corel
Corning Incorporated
CTG, Inc.
Cypress Semiconductor Corp.
Dell
Diode Inc
eBay
EDS
Electronic Arts
EMC Corp
Exabyte Corporation
Fiserv
Freescale Semiconductor, Inc.
Gateway, Inc.
Google
Hewlett-Packard
IBM
IDT Corporation
Imation
Ingram Micro
Intel Corp.
Intergraph
Intuit Inc.
Iomega Corp.
Komag, Incorporated
LAM Research
Lexmark
Logitech
LSI
Lucent
McAfee
MEMC Electronic Materials, Inc.
Mentor Corporation
Micron Technology
Microsoft
Motorola
N-C-R
National Semiconductor
Network Equipment Technologies, Inc.
Nextel Communications
Nortel
Novell
NVIDIA Corporation
Oracle Corp.
Palm, Inc.
Qualcomm
Quantum
Redback Networks Inc.
SanDisk
Sanmina SCI
Seagate
Silicon Graphics
Solectron Global Systems
Sprint
SSA Global
Sun Microsystems
Sybase
Symantec
Symbol Corp.
SYNNEX Corporation
Synopsys
Tektronix, Inc.
Tellabs Operations Inc
Texas Instruments Incorporated
Transmeta
Unisys
VeriSign
Verizon
Western Digital
Xerox
Xilinx
Yahoo
http://undress4success.com/individuals/bet-work-home-employers/top-100-computer-companies/
07-26-10

What is a database

2010-07-03T01:34:00.005-04:00

Many people are first exposed to databases by playing with Access, which comes included in many versions of Microsoft Office. Access is a powerful product aimed primarily at developers, and many novices come away from dabbling with it determined to stick to more user-friendly packages such as Excel.

That attitude might be OK for individual users, but most small businesses will eventually find themselves contemplating database software as their needs grow and their companies expand. But before you can even go about installing a database, you need to grapple with such confusing concepts as database servers, relational and object databases, and the thorny question of why apparently similar products range in price from free to hundreds of thousands of dollars.

This Buying Guide will help you through the database minefield. While picking a database server will never be as quick a decision as, say, buying a printer, it can be a highly valuable purchase if you go about it the right way.

What is a database? (Back to contents)

A database is simply an organised set of information. Strictly speaking, there's no need for it to even be in computerised form - address books are often used as a simple example of a database, since they contain large volumes of information organised into categories (name, address, and phone number). Despite this, most people now take the term 'database' to refer to information stored electronically.

Note also that the general definition of a database given here could encompass many common PC applications, such as electronic mail (which can be organised by recipient or sender) or information in a spreadsheet (which tends to be structured mathematically). In practice, the term 'database' is most commonly used to refer to highly structured information (examples might include order forms or medical information). Most business databases will contain a carefully planned set of information that can be analysed to indicate overall trends, as well as providing a historical record of past transactions and activities.

A basic database system simply allows you to enter and search for information (a process often known as querying). Most modern databases also support the development of specific applications that run on top of the database, which enable you to access the features you need without having to worry about all the complexities of the system. For instance, within one company general staff might have access to an order entry system, while financial staff have access to automatic reporting systems that provide sales summaries and other information. Both use a database server to store information, but the means of entering this, and the ability to change it after entry, will vary between the different applications.

The types of databases available

As database software has evolved, a number of different approaches to storing and linking information have emerged. Some of the more common include:

Relational databases. A relational database creates formal definitions of all the included items in a database, setting them out in tables, and defines the relationship between them. For instance, a typical business database would include tables for defining both customers and orders. Using ids or keys, the two tables can be related together. Such databases are called 'relational' because they explicitly define these connections (an order form can look up customer details from the customer table rather than having to store the information twice). Most relational databases now make use of SQL to handle queries (discussed in more detail below). Currently these are the most common form of database.

Object databases. Object databases store data in discreet, self-contained units - objects. These objects have specific data, attributes and behaviours associated with them. An extremely simple example might be a product database with a shirt object, which has attributes such as size, colour, and price. In practical use, the main difference between object and relational databases is the way in which data is accessed. Programmers use object-oriented programming languages to access the data objects from the object database by calling methods in their code. This takes much of the information that would have resided in the application code and transfers that information to the object database. Thus the application code is simplified. However, at the same time the fact that the database and application are tightly entwined can make accessing the data outside of the application more complex.

Object-relational databases. Object-relational databases attempt to combine object and relational approaches. This allows the benefits of using objects where necessary to be tied to the strengths of relational databases.

Hierarchical databases. While relational databases arrange data in tabular format, hierarchical databases arrange them in a tree format, with a parent node leading to further child nodes (which in turn may have further nodes of their own). The model is very similar to the way in which a program such as Windows Explorer displays the contents of a hard drive (double-clicking on a parent directory leads down the tree to further information, and so on down the directory tree). This allows for multiple types of subsidiary data, but makes it difficult to identify complex multiple relationships between individual data items (just as there is no obvious link between two subdirectories on a hard drive).

Until recently, hierarchical databases have been more common in computer science fields than in real-world applications. However, hierarchical methods have become more popular with the emergence of XML (Extensible Markup Language), which uses a hierarchical structure, as a common data exchange format.

http://qualityitconcepts1.blogspot.com/2010/07/different-kinds-of-databases.html

07/03/10

Database and why it is important

2010-07-03T00:24:00.001-04:00

A database consists of an organized collection of data for one or more multiple uses. One way of classifying databases involves the type of content, for example: bibliographic, full-text, numeric, image. Other classification methods start from examining database models or database architectures: see below. Software organizes the data in a database according to a database model. As of 2010 the relational model occurs most commonly. Other models such as the hierarchical model and the network model use a more explicit representation of relationships.
A database management system (DBMS) consists of software that organizes the storage of data. A DBMS controls the creation, maintenance, and use of the database storage structures of social organizations and of their users. It allows.
When we maintain a small table of data, it could be easily accessed through MS Excel. However, this is not possible if we maintain large data as it simply takes much time to retrieve.

when we maintain a large business data through a database using a tool like My SQL, we can add, update, delete or retrieve any data within seconds using a language like SQL.

Also, we can link various databases for our convenience.

Database management systems perform a multitude of functions including providing security, multi-user access, it also transforms data into information. Database management systems also manage data stored and contains programming languages.

07/02/10

What is Webmail (or Web-based e-mail)

2010-06-24T14:59:00.004-04:00

Webmail (or Web-based e-mail) is an e-mail service intended to be primarily accessed via a web browser, as opposed to through a desktop e-mail client (such as Microsoft Outlook, Pegasus Mail, Mozilla's Thunderbird, or Apple Inc.'s Mail). Very popular webmail providers include Gmail, Yahoo! Mail, Hotmail, and AOL Mail.^[1]
One advantage of webmail over application-based e-mail is that a user has the ability to access their inbox from any Internet-connected computer around the world. However, the need for Internet access is also a drawback, in that one cannot access old messages when not connected to the Internet (with the exception of some newer technologies, such as Gmail's "Offline Mail"^[2] feature). On the other hand, if one uses the IMAP protocol through an application-based e-mail client, all contents of the mailbox will be consistently displayed in both the webmail and the PC e-mail client contexts.
In 1997, before its acquisition by Microsoft, Hotmail (now Windows Live Hotmail) introduced its service, which became one of the first popular web-based e-mail offerings. Following Hotmail's success, Google's introduction of Gmail in 2004 sparked a period of rapid development in webmail, due to Gmail's new features such as JavaScript menus, text-based ads, and bigger storage.

[hide]

[edit] History

The first webmail software was called WWW Mail^[3] and was developed in perl by Soren Vejrum when he was studying and working at the Copenhagen Business School in Denmark. The development started in 1994 and after a period of personal use the first public version was released with freely downloadable source code on February 28, 1995.^[4]
The second webmail software was called WebMail and was developed in perl by Luca Manunza^[5]^[6] when he was working at CRS4, in Sardinia. The first working demo^[7] was released on March 10, 1995; thereafter the source^[8] was released (with registration required) on March 30, 1995.

[edit] Software packages

There are also software packages that allow organizations to offer e-mail through the web for their associates. Some solutions are open source software like Atmail, SquirrelMail, RoundCube, BlueMamba, IlohaMail, and UebiMiau, while others are commercial open source like Atmail or closed source like the Outlook Web Access module for Microsoft Exchange. Conversely, there are programs that can simulate a web browser to access webmail as if it were stored in a POP3 or IMAP account. They are susceptible, though, to changes in the user interface of the web service since there is no standard interface.
Some providers offer web access to other's e-mail servers. This allows web access to mailboxes where the mail server does not offer a web interface, or where an alternative interface is desired.

[edit] Rendering and compatibility

There are important differences in rendering capabilities for many popular webmail services such as Yahoo Mail, Gmail, and Windows Live Hotmail. Due to the various treatment of HTML tags, such as

http://en.wikipedia.org/wiki/E-mail
06/02/10

What is stand by mode on a computer

2010-06-23T19:11:00.001-04:00

Computers

Sleep mode can go by many different names, including Stand By (for Microsoft Windows 95-Server 2003), Sleep (for Mac OS 8)-(Mac OS X, Windows Vista, Windows 7, Windows Server 2008), and Suspend (Linux). When placed in this Sleep mode, aside from the RAM which is required to restore the machine's state, the computer attempts to cut power to all unneeded parts of the machine. Because of the large power savings, most laptops automatically enter this mode when the computer is running on batteries and the lid is closed.
Though Sleep and Hibernate are generally thought as two separate functions, modern Macintoshes, Windows Vista (termed Hybrid Sleep), and some specially configured Linux machines also feature a variation of Sleep mode that incorporates the strengths of Hibernate. The RAM is copied to the hard drive before sleep mode is initiated, preserving the RAM contents in the event of a power loss.
ACPI is the current standard for power management, superseding APM and providing the backbone for sleep and hibernation on modern computers. Sleep mode corresponds to ACPI mode S3. When a non-ACPI device is plugged in, Windows will sometimes disable stand-by functionality for the whole operating system. Without ACPI functionality, as seen on older hardware, sleep mode is usually restricted to turning off the monitor and spinning down the hard drive.

[edit] Sleep Mode Testing

In the first years of introduction of sleep mode in the consumer market, it was usually not tested as thoroughly as the normal mode, causing various problems especially with peripherals like computer mice. Partly for these reasons, in industrial machines sleep mode was generally avoided because the costs associated with wasted time and materials far outweighed the savings in energy from sleep mode.

[edit] See also

Hibernation (computing)
Green computing
One Watt Initiative
Linux implementations of Sleep/Suspend/Hibernate
- TuxOnIce
- swsusp
Standby power

http://en.wikipedia.org/wiki/Sleep_mode
06/23/10

Web Site Hosting

2010-06-23T19:07:00.001-04:00

File hosting service (redirect from Web storage)

A file hosting service, online file ... large files that are not web pages. ... Services offered: These sites are often used for web hosting . ...
8 KB (1,149 words) - 18:40, 10 June 2010
Web hosting service (redirect from Web hosting)

A web hosting service is a type of Internet hosting service that allows ... Personal web site hosting is typically free, advertisement- ...
11 KB (1,468 words) - 05:01, 22 June 2010
Domain name (redirect from Web site name)

Use in web site hosting: A domain name is a component of a Uniform Resource Locator (URL) used to access web site s, for example ...
26 KB (3,750 words) - 19:29, 22 June 2010
Web traffic (section Increase web site traffic)

Web traffic is the amount of data sent and received by visitors to a web site . ... individual leasing the bandwidth from an ISP or hosting site. ...
12 KB (1,857 words) - 21:03, 18 June 2010
Sesame Street (section Web site)

mail than any of the show's human hosts, on its cover and declared, " .. ... "Web site : Since 1998 Sesame Workshop has provided additional ...
77 KB (10,892 words) - 20:34, 18 June 2010
Website (redirect from Web site)

A website (also spelled Web site; officially styled website by the AP Stylebook ) is ... A web site is hosted on at least one web server , ...
23 KB (3,271 words) - 16:28, 21 June 2010
SNL Financial

SNL’s products include an online database with real-time news and analytical tools; investor relations Web site hosting; electronic ...
7 KB (927 words) - 19:10, 28 October 2009
Orbitel

Orbitel also provides services such as web site hosting, domain registration, corporate e-mail and professional consultations. ...
6 KB (758 words) - 21:31, 17 November 2009
Aljazeera (section Web site attacks)

The English-language site was forced to change internet hosting ... Web site attacks: Immediately after its launch in 2003, the English site was ...
67 KB (9,373 words) - 11:30, 18 June 2010
2008 Democratic National Convention (section Web Site)

Convention Denver last hosted the Democratic National Convention in 1908 . ... Criticisms Web Site: for the convention web site, along with ...
49 KB (6,809 words) - 16:08, 26 May 2010
International Lyrics Server

The International Lyrics Server was a Swiss web site devoted to hosting user-supplied song lyrics . it was hosting over 100,000 song s ...
1 KB (150 words) - 05:05, 26 November 2009
Congress of Industrial Organizations (section Web sites)

Web sites : http://www. library. gsu. edu/spcoll/labor/wnp/ Work'n'Progress: ... University of California (hosted), Gerhard Peters (database).
33 KB (5,203 words) - 21:45, 11 June 2010
Blue Network (section Web sites)

for the first broadcast It was hosted by Johnny Olson , who would ... Web sites : last Haendiges | first Jerry | title Vintage Radio Logs | url ...
78 KB (12,148 words) - 01:17, 7 June 2010
National Film Board of Canada (section NFB Web Sites)

international web users the ability ... in blogs and social sites In October ... Various festivals, film exhibits and university clubs host ...
37 KB (5,176 words) - 18:32, 16 June 2010
Baseball Prospectus (section Web site)

Web site ... who since 2003 has written the "Under The Knife" daily column, a summary of injury news, and is a host of Baseball Prospectus Radio. ...
52 KB (7,623 words) - 06:58, 21 June 2010
Fuel TV (section Web site)

The shows host is an adult seemingly in his early 20's. ... Digital media Web site : Fuel TV's website includes extreme sports events listings, ...
16 KB (2,433 words) - 01:28, 8 June 2010
Planet Half-Life (section Site hosting)

Site hosting ... The web hosting is regulated through GameSpy , though the address of hosted sites is a subset of the Planet Half-Life domain. ...
12 KB (1,810 words) - 03:19, 14 January 2010
Hyperborean cycle (section Web sites)

A host of other deities play important roles in the cycle; foremost ... Web sites : author Cornford, Laurence J | title A Hyperborean Glossary | ...
12 KB (1,754 words) - 12:19, 25 February 2010
CPanel (redirect from Web host manager)

web hosting control panel that provides a graphical interface and automation tools designed to simplify the process of hosting a web site. ...
6 KB (577 words) - 11:23, 22 May 2010
Openwares.org

org is a public Open Source and Freeware software development web site, providing free publishing , packaging , hosting , and marketing ...
2 KB (254 words) - 11:33, 18 February 2010
http://en.wikipedia.org/wiki/Special:Search?search=Web+Site+Hosting&sourceid=Mozilla-search
06/23/10

What is a GIF Image

2010-06-10T14:30:00.002-04:00

Definitions of .gif on the Web:

The Graphics Interchange Format (GIF) is a bitmap image format that was introduced by CompuServe in 1987 and has since come into widespread usage on the World Wide Web due to its wide support and portability.
en.wikipedia.org/wiki/.gif
A bitmap image format for pictures with up to 256 distinct colors
en.wiktionary.org/wiki/GIF
A format for pictures transmitted pixel by pixel over the Net. Created by CompuServe, the GIF specification was put into the public domain, but Unisys found that it had a patent on the compression technology used. This stimulated the development of PNG.
www.w3.org/People/Berners-Lee/Weaving/glossary.html
An industry standard raster graphic or image format.
www.geom.unimelb.edu.au/gisweb/glossary.htm
Graphical Interchange Format. Developed in 1987 by CompuServe, this is a way of storing compressed images with up to 256 colors. It became popular on the Web because it was the only format that could be displayed in-line by the first multi-platform Web browser (NCSA Mosaic). ...
philip.greenspun.com/panda/glossary
Graphics Interchange Format: lossy compression algorithm, supports 1-8 bit depth, 256 index color only
authors.nejm.org/help/techglossary.asp
A universal computer file format used for raster, or bit map, artwork, primarily for the Web.
web.mit.edu/graphicidentity/glossary/index.html
An image file format compatible with web browsers.
swdb.berkeley.edu/glossary.html
Graphical Information Format. Most common image format used on Internet. Developed by Compuserve. Main advantage is that GIF images occupy relatively little file space.
www.nwas.org/committees/rs/glossary.html
(graphics interchange format): pronounced 'jiff' or 'giff.' Includes data compression and is suited for simple graphics where the colors are limited. The images may be animated or transparent. Generally not suited for photographs, however.
www.gslis.utexas.edu/~vlibrary/glossary/index.html
A GIF file is mostly suitable for graphics and to a lesser extent for photo's. The GIF format has a maximum of 256 colors which decreases the size of the file.
www.proefschriftgroningen.nl/terminology.php
Term for "Graphics Interchange Format". GIF is used to compress data. Most generally used for banner advertising.
www.wnd.com/mediakit/glossary.asp
This is a widely used graphics format for the Internet that allows transparency and animation. The limitation of this format is that it the maximum number of colors is 256. GIFs are often dithered, which can give the illusion of more colors.
www.adigitaldreamer.com/2/graphicdesignglossary.htm
A compressed file format used for logos and drawings.
www.telecomsadvice.org.uk/glossary/g.html
The Growth and Innovation Framework was released in February 2002 to set out the government's sustainable economic growth objectives. The framework laid out what the government and the private sector must do to achieve higher sustainable economic growth. ...
www.digitalstrategy.govt.nz/Resources/Glossary-of-Key-Terms/

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06/11/10

What are JPEG Images

2010-06-10T14:28:00.003-04:00

Definitions of JPEG on the Web:

In computing, JPEG (, ) (named after the Joint Photographic Experts Group who created the standard) is a commonly used method of lossy compression for photographic images. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. ...
en.wikipedia.org/wiki/JPEG
A file format commonly used for image compression; An image file in that format
en.wiktionary.org/wiki/JPEG
This group defined a format for encoding photographs that uses fewer bytes than the pixel-by-pixel approaches of GIF and PNG, without too much visible degradation in quality. The format (JFIF) is casually referred to as JPEG. About JPEG pointers from W3C
www.w3.org/People/Berners-Lee/Weaving/glossary.html
Joint Photographic Expert Group - a compression algorithm for condensing the size of image files. JPEGs are very helpful in allowing access to full-screen image files on-line because they require less storage and therefore are quicker to download into a web page.
www.nebraskahistory.org/lib-arch/research/photos/digital/glossary.htm
A lossy compression technique that can reduce the size of a graphics file by as much as 96 %.
publications.europa.eu/vademecum/vademecum/9313fdfe-c49e-119e-45c6a6441e63e066_en.html
JPEG is an image format, useful for making high-quality photographic- style images of relatively small file size.
www.bradley.edu/help/glossary.html
JPEG is a file format used primarily to compress photographic images. JPEGs reduce the original image size by subdividing and simplifying complex images, allowing them to transfer more quickly across an Internet connection. ...
www.texastech.edu/identityguidelines/glossary.php
is an industry standard for compressing images. This format provides lossy compression (you lose sharpness from the original) by dividing the image into tiny pixel blocks, which are halved over and over until an adequate compression ratio is achieved.
www.ti.com/corp/docs/investor/dsp/glossary.htm
Joint Photographers' Expert Group - a type of compression that minimizes the amount of color information in your image that is actually not distinguishable by the human eye. JPEG compression rates can be very high, although using it too many times on the same image will result in a loss of quality.
www.uic.edu/depts/adn/seminars/webgraphics/glossary.html
was formed to create a standard for color and gray scale image compression. JPEG describes a variety of algorithms (rules), each of which is targeted for a specific type of image application. JPEG is the default format for most digital cameras. JPEG 2000 is the latest version. ...
www.bostonprintbuyers.com/resources/glossary/j.html
Easily compressed graphics format that displays photographic as well as graphic images. JPEG is a newer format than GIF. Up
www.adserversolutions.com/adserver/adterms2.html
Joint Photographic Expert Group. A graphical file format used to display high-resolution colour images on the World Wide Web.
www.netsetgo.com/glossary.php
compression; Joint Photographic Experts Group
www.epa.gov/records1/gloss/gloss00.htm
A common process for compressing digital images.
www.youthedesigner.com/2007/09/22/design-terms/
An industry standard file type that can be shared across the internet and between computers. Unlike some proprietary file types, most computers can open and view .jpg picture files without having to install other software to be able to view the file. ...
support.visioneer.com/KnowledgeBase/glossary.asp

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06/11/10

NIC Card

2010-06-09T14:56:00.000-04:00

Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name came from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model as well as a common addressing format and Media Access Control at the Data Link Layer.
Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. It has been used from around 1980^[1] to the present, largely replacing competing LAN standards such as token ring, FDDI, and ARCNET.

A standard 8P8C (often called RJ45) connector used most commonly on cat5 cable, a type of cabling used primarily in Ethernet networks.

The Internet Protocol Suite
Application Layer
BGP · DHCP · DNS · FTP · GTP · HTTP · IMAP · IRC · LDAP · Megaco · MGCP · NNTP · NTP · POP · RIP · RPC · RTP · RTSP · SDP · SIP · SMTP · SNMP · SOAP · SSH · Telnet · XMPP · (more)
Transport Layer
TCP · UDP · DCCP · SCTP · RSVP · TLS/SSL · ECN · (more)
Internet Layer
IP (IPv4, IPv6) · ICMP · ICMPv6 · IGMP · IPsec · (more)
Link Layer
ARP/InARP · NDP · OSPF · Tunnels (L2TP) · PPP · Media Access Control (Ethernet, DSL, ISDN, FDDI) · (more)
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[edit] History

Ethernet was developed at Xerox PARC between 1973 and 1975.^[2] It was inspired by ALOHAnet which Robert Metcalfe had studied as part of his Ph. D. dissertation.^[3] In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker and Butler Lampson as inventors.^[4] In 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper.^[5]^{[note 1]}
Metcalfe left Xerox in 1979 to promote the use of personal computers and local area networks (LANs), forming 3Com. He convinced Digital Equipment Corporation (DEC), Intel, and Xerox to work together to promote Ethernet as a standard, the so-called "DIX" standard, for "Digital/Intel/Xerox"; it specified the 10 megabits/second Ethernet, with 48-bit destination and source addresses and a global 16-bit Ethertype type field. The first standard draft was first published on September 30, 1980 by the Institute of Electrical and Electronics Engineers (IEEE).^{[citation needed]} Support of Ethernet's carrier sense multiple access with collision detection (CSMA/CD) in other standardization bodies (i.e. ECMA, IEC and ISO) was instrumental in getting past delays of the finalization of the Ethernet standard due to the difficult decision processes in the IEEE, and due to the competitive Token Ring proposal strongly supported by IBM.^{[citation needed]} Ethernet initially competed with two largely proprietary systems, Token Ring and Token Bus. These proprietary systems soon found themselves buried under a tidal wave of Ethernet products. In the process, 3Com became a major company. 3Com built the first 10 Mbit/s Ethernet adapter (1981).^{[citation needed]} This was followed quickly by DEC's Unibus to Ethernet adapter, which DEC sold and used internally to build its own corporate network, which reached over 10,000 nodes by 1986; far and away the largest extant computer network in the world at that time.^{[citation needed]}
Through the first half of the 1980s, Digital's Ethernet implementation utilized a coaxial cable about the diameter of a US nickel which became known as Thick Ethernet when its successor, Thinnet Ethernet was introduced. Thinnet uses a cable similar to cable television cable of the era. The emphasis was on making installation of the cable easier and less costly.
The observation that there was plenty of excess capacity in unused unshielded twisted pair (UTP) telephone wiring already installed in commercial buildings provided another opportunity to expand the installed base and thus twisted-pair Ethernet was the next logical development in the mid 1980s, beginning with StarLAN. UTP-based Ethernet became widely known with 10BASE-T standard. This system replaced the coaxial cable systems with a system of hubs linked via UTP.
In 1990, Kalpana introduced the first Ethernet switch^[6] which replaced the CSMA/CD scheme in favor of a switched full duplex system offering higher performance and at a lower cost than using routers.

[edit] Standardization

Notwithstanding its technical merits, timely standardization was instrumental to the success of Ethernet. It required well-coordinated and partly competitive activities in several standardization bodies such as the IEEE, ECMA, IEC, and finally ISO.
In February 1980 IEEE started a project, IEEE 802, for the standardization of local area networks (LAN).^[7]
The "DIX-group" with Gary Robinson (DEC), Phil Arst (Intel) and Bob Printis (Xerox) submitted the so-called "Blue Book" CSMA/CD specification as a candidate for the LAN specification. Since IEEE membership is open to all professionals, including students, the group received countless comments on this brand-new technology.
In addition to CSMA/CD, Token Ring (supported by IBM) and Token Bus (selected and henceforward supported by General Motors) were also considered as candidates for a LAN standard. Due to the goal of IEEE 802 to forward only one standard and due to the strong company support for all three designs, the necessary agreement on a LAN standard was significantly delayed.
In the Ethernet camp, it put at risk the market introduction of the Xerox Star workstation and 3Com's Ethernet LAN products. With such business implications in mind, David Liddle (General Manager, Xerox Office Systems) and Metcalfe (3Com) strongly supported a proposal of Fritz Röscheisen (Siemens Private Networks) for an alliance in the emerging office communication market, including Siemens' support for the international standardization of Ethernet (April 10, 1981). Ingrid Fromm, Siemens representative to IEEE 802 quickly achieved broader support for Ethernet beyond IEEE by the establishment of a competing Task Group "Local Networks" within the European standards body ECMA TC24. As early as March 1982 ECMA TC24 with its corporate members reached agreement on a standard for CSMA/CD based on the IEEE 802 draft. The speedy action taken by ECMA decisively contributed to the conciliation of opinions within IEEE and approval of IEEE 802.3 CSMA/CD by the end of 1982.
Approval of Ethernet on the international level was achieved by a similar, cross-partisan action with Fromm as liaison officer working to integrate IEC TC83 and ISO TC97SC6, and the ISO/IEEE 802/3 standard was approved in 1984.

[edit] General description

A 1990s network interface card. This is a combination card that supports both coaxial-based using a 10BASE2 (BNC connector, left) and twisted pair-based 10BASE-T, using an RJ45 (8P8C modular connector, right).

Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium. The methods used show some similarities to radio systems, although there are fundamental differences, such as the fact that it is much easier to detect collisions in a cable broadcast system than a radio broadcast. The common cable providing the communication channel was likened to the ether and it was from this reference that the name "Ethernet" was derived.
The advantage of CSMA/CD was that, unlike Token Ring and Token Bus, all nodes could "see" each other directly. All "talkers" shared the same medium - a single coaxial cable - however, this was also a limitation; with only one speaker at a time, packets had to be of a minimum size to guarantee that the leading edge of the propagating wave of the message got to all parts of the medium before the transmitter could stop transmitting, thus guaranteeing that collisions (two or more packets initiated within a window of time which forced them to overlap) would be discovered. Minimum packet size and the physical medium's total length were thus closely linked.
From this early and comparatively simple concept, Ethernet evolved into the complex networking technology that today underlies most LANs. The coaxial cable was replaced with point-to-point links connected by Ethernet hubs and/or switches to reduce installation costs, increase reliability, and enable point-to-point management and troubleshooting. StarLAN was the first step in the evolution of Ethernet from a coaxial cable bus to a hub-managed, twisted-pair network. The advent of twisted-pair wiring dramatically lowered installation costs relative to competing technologies, including the older Ethernet technologies.
Above the physical layer, Ethernet stations communicate by sending each other data packets, blocks of data that are individually sent and delivered. As with other IEEE 802 LANs, each Ethernet station is given a single 48-bit MAC address, which is used to specify both the destination and the source of each data packet. Network interface cards (NICs) or chips normally do not accept packets addressed to other Ethernet stations. Adapters generally come programmed with a globally unique address, but this can be overridden, either to avoid an address change when an adapter is replaced, or to use locally administered addresses.
Despite the significant changes in Ethernet from a thick coaxial cable bus running at 10 Mbit/s to point-to-point links running at 1 Gbit/s and beyond, all generations of Ethernet (excluding early experimental versions) share the same frame formats (and hence the same interface for higher layers), and can be readily interconnected.
Due to the ubiquity of Ethernet, the ever-decreasing cost of the hardware needed to support it, and the reduced panel space needed by twisted pair Ethernet, most manufacturers now build the functionality of an Ethernet card directly into PC motherboards, eliminating the need for installation of a separate network card.

[edit] Dealing with multiple clients

[edit] CSMA/CD shared medium Ethernet

Ethernet originally used a shared coaxial cable (the shared medium) winding around a building or campus to every attached machine. A scheme known as carrier sense multiple access with collision detection (CSMA/CD) governed the way the computers shared the channel. This scheme was simpler than the competing token ring or token bus technologies. When a computer wanted to send some information, it used the following algorithm:

[edit] Main procedure

Frame ready for transmission.
Is medium idle? If not, wait until it becomes ready and wait the interframe gap period (9.6 µs in 10 Mbit/s Ethernet).
Start transmitting.
Did a collision occur? If so, go to collision detected procedure.
Reset retransmission counters and end frame transmission.

[edit] Collision detected procedure

Continue transmission until minimum packet time is reached (jam signal) to ensure that all receivers detect the collision.
Increment retransmission counter.
Was the maximum number of transmission attempts reached? If so, abort transmission.
Calculate and wait random backoff period based on number of collisions.
Re-enter main procedure at stage 1.

This can be likened to what happens at a dinner party, where all the guests talk to each other through a common medium (the air). Before speaking, each guest politely waits for the current speaker to finish. If two guests start speaking at the same time, both stop and wait for short, random periods of time (in Ethernet, this time is generally measured in microseconds). The hope is that by each choosing a random period of time, both guests will not choose the same time to try to speak again, thus avoiding another collision. Exponentially increasing back-off times (determined using the truncated binary exponential backoff algorithm) are used when there is more than one failed attempt to transmit.
Computers were connected to an Attachment Unit Interface (AUI) transceiver, which was in turn connected to the cable (later with thin Ethernet the transceiver was integrated into the network adapter). While a simple passive wire was highly reliable for small Ethernets, it was not reliable for large extended networks, where damage to the wire in a single place, or a single bad connector, could make the whole Ethernet segment unusable. Multipoint systems are also prone to very strange failure modes when an electrical discontinuity reflects the signal in such a manner that some nodes would work properly while others work slowly because of excessive retries or not at all (see standing wave for an explanation of why); these could be much more painful to diagnose than a complete failure of the segment. Debugging such failures often involved several people crawling around wiggling connectors while others watched the displays of computers running a ping command and shouted out reports as performance changed.
Since all communications happen on the same wire, any information sent by one computer is received by all, even if that information is intended for just one destination. The network interface card interrupts the CPU only when applicable packets are received: the card ignores information not addressed to it unless it is put into "promiscuous mode". This "one speaks, all listen" property is a security weakness of shared-medium Ethernet, since a node on an Ethernet network can eavesdrop on all traffic on the wire if it so chooses. Use of a single cable also means that the bandwidth is shared, so that network traffic can slow to a crawl when, for example, the network and nodes restart after a power failure.

[edit] Repeaters and hubs

Main article: Ethernet hub

For signal degradation and timing reasons, coaxial Ethernet segments had a restricted size which depended on the medium used. For example, 10Base5 coax cables had a maximum length of 500 meters (1,640 ft) and 10Base2 coax cables had a maximum length of 185 meters (607 ft). Also, as was the case with most other high-speed buses, Ethernet segments had to be terminated with a resistor at each end. For coaxial-cable-based Ethernet, each end of the cable had a 50 ohm (Ω) resistor attached. Typically this resistor was built into a male BNC or N connector and attached to the last device on the bus, or, if vampire taps were in use, to the end of the cable just past the last device. If termination was not done, or if there was a break in the cable, the AC signal on the bus was reflected, rather than dissipated, when it reached the end. This reflected signal was indistinguishable from a collision, and so no communication would be able to take place.
Terminators had a metallic chain attached to them for grounding purposes, however many people never understood how to properly ground cabling and thus grounded the terminators at both ends rather than just one end. This caused many of the grounding loop problems during that era which caused network outages and/or data corruption when swells of electricity traversed the coaxial cabling's outer shield on its path to the ground with the least resistance.
A greater cabling length could be obtained by an Ethernet repeater, which took the signal from one Ethernet cable and repeated it onto another cable. If a collision was detected, the repeater transmitted a jam signal onto all ports (initial repeaters only had 2 ports but they gave way to 4-, 6-, 8-ports and more) to ensure collision detection. Repeaters could be used to transparently connect segments such that up to five Ethernet segments could be inter-joined between any two hosts, of which 3 of those segments could have attached devices and the other 2 segments were only used to increase distance, but would not have any hosts attached (i.e. only repeaters attached at each end). Repeaters could detect an improperly terminated link from the continuous collisions and stop forwarding data from it. Hence they alleviated the problem of cable breakages: when an Ethernet coax segment broke, while all devices on that segment were unable to communicate, repeaters allowed the other segments to continue working - although depending on which segment was broken and the layout of the network the partitioning that resulted may have made other segments unable to reach important servers and thus effectively useless.
The Ethernet 5-4-3 Rule was made following this standard to make it easier to remember. The "5" was the maximum number of segments which could be connected on a single network. The "4" was the maximum number of repeaters which could be used on that network. And the "3" was the maximum number of populated (segments with hosts attached) segments on that network.
People recognized the advantages of cabling in a star topology, primarily that only faults at the star point will result in a badly partitioned network, and network vendors began creating repeaters having multiple ports, thus reducing the number of repeaters required at the star point. Multiport Ethernet repeaters became known as "Ethernet hubs" with repeaters built into the hub itself. Network vendors such as DEC and SynOptics sold hubs that connected many 10Base5 thick coaxial and 10Base2 thin coaxial segments. There were also "multiport transceivers" or "fan-outs". These could be connected to each other and/or a coax backbone. A well-known early example was DEC's DELNI. These devices allowed multiple hosts with AUI connections to share a single transceiver. They also allowed creation of a small standalone Ethernet segment without using a coaxial backbone cable.

A twisted pair Cat-3 or Cat-5 cable is used to connect 10BASE-T Ethernet

Ethernet on unshielded twisted-pair cables (UTP), beginning with StarLAN and continuing with 10BASE-T, was designed for point-to-point links only and all termination was built into the device. This changed hubs from a specialist device used at the center of large networks to a device that every twisted pair-based network with more than two machines had to use. The tree structure that resulted from this made Ethernet networks more reliable by preventing faults with (but not deliberate misbehavior of) one peer or its associated cable from affecting other devices on the network, although a failure of a hub or an inter-hub link could still affect lots of users. Also, since twisted pair Ethernet is point-to-point and terminated inside the hardware, the total empty panel space required around a port is much reduced, making it easier to design hubs with lots of ports and to integrate Ethernet onto computer motherboards.
Despite the physical star topology, hubbed Ethernet networks still use half-duplex and CSMA/CD, with only minimal activity by the hub, primarily the Collision Enforcement signal, in dealing with packet collisions. Every packet is sent to every port on the hub, so bandwidth and security problems aren't addressed. The total throughput of the hub is limited to that of a single link and all links must operate at the same speed.
Collisions reduce throughput by their very nature. In the worst case, when there are lots of hosts with long cables that attempt to transmit many short frames, excessive collisions can reduce throughput dramatically. However, a Xerox report in 1980 summarized the results of having 20 fast nodes attempting to transmit packets of various sizes as quickly as possible on the same Ethernet segment.^[8] The results showed that, even for the smallest Ethernet frames (64 Bytes), 90% throughput on the LAN was the norm. This is in comparison with token passing LANs (token ring, token bus), all of which suffer throughput degradation as each new node comes into the LAN, due to token waits.
This report was controversial, as modeling showed that collision-based networks became unstable under loads as low as 40% of nominal capacity. Many early researchers failed to understand the subtleties of the CSMA/CD protocol and how important it was to get the details right, and were really modeling somewhat different networks (usually not as good as real Ethernet).^[9]

[edit] Bridging and switching

Main articles: Ethernet switch and Ethernet bridge

While repeaters could isolate some aspects of Ethernet segments, such as cable breakages, they still forwarded all traffic to all Ethernet devices. This created practical limits on how many machines could communicate on an Ethernet network. Also as the entire network was one collision domain and all hosts had to be able to detect collisions anywhere on the network, the number of repeaters between the farthest nodes was limited. Finally segments joined by repeaters had to all operate at the same speed, making phased-in upgrades impossible.
To alleviate these problems, bridging was created to communicate at the data link layer while isolating the physical layer. With bridging, only well-formed Ethernet packets are forwarded from one Ethernet segment to another; collisions and packet errors are isolated. Bridges learn where devices are, by watching MAC addresses, and do not forward packets across segments when they know the destination address is not located in that direction.
Prior to discovery of network devices on the different segments, Ethernet bridges (and switches) work somewhat like Ethernet hubs, passing all traffic between segments. However, as the bridge discovers the addresses associated with each port, it only forwards network traffic to the necessary segments, improving overall performance. Broadcast traffic is still forwarded to all network segments. Bridges also overcame the limits on total segments between two hosts and allowed the mixing of speeds, both of which became very important with the introduction of Fast Ethernet.
Early bridges examined each packet one by one using software on a CPU, and some of them were significantly slower than hubs (multi-port repeaters) at forwarding traffic, especially when handling many ports at the same time. This was in part due to the fact that the entire Ethernet packet would be read into a buffer, the destination address compared with an internal table of known MAC addresses and a decision made as to whether to drop the packet or forward it to another or all segments.
In 1989 the networking company Kalpana introduced their EtherSwitch, the first Ethernet switch. This worked somewhat differently from an Ethernet bridge, in that only the header of the incoming packet would be examined before it was either dropped or forwarded to another segment. This greatly reduced the forwarding latency and the processing load on the network device. One drawback of this cut-through switching method was that packets that had been corrupted at a point beyond the header could still be propagated through the network, so a jabbering station could continue to disrupt the entire network. The remedy for this was to make available store-and-forward switching, where the packet would be read into a buffer on the switch in its entirety, verified against its checksum and then forwarded. This was essentially a return to the original approach of bridging, but with the advantage of more powerful, application-specific processors being used. Hence the bridging is then done in hardware, allowing packets to be forwarded at full wire speed. It is important to remember that the term switch was invented by device manufacturers and does not appear in the 802.3 standard.
Since packets are typically only delivered to the port they are intended for, traffic on a switched Ethernet is slightly less public than on shared-medium Ethernet. Despite this, switched Ethernet should still be regarded as an insecure network technology, because it is easy to subvert switched Ethernet systems by means such as ARP spoofing and MAC flooding. The bandwidth advantages, the slightly better isolation of devices from each other, the ability to easily mix different speeds of devices and the elimination of the chaining limits inherent in non-switched Ethernet have made switched Ethernet the dominant network technology.
When a twisted pair or fiber link segment is used and neither end is connected to a hub, full-duplex Ethernet becomes possible over that segment. In full duplex mode both devices can transmit and receive to/from each other at the same time, and there is no collision domain. This doubles the aggregate bandwidth of the link and is sometimes advertised as double the link speed (e.g. 200 Mbit/s) to account for this. However, this is misleading as performance will only double if traffic patterns are symmetrical (which in reality they rarely are). The elimination of the collision domain also means that all the link's bandwidth can be used and that segment length is not limited by the need for correct collision detection (this is most significant with some of the fiber variants of Ethernet).

[edit] More advanced networks

Simple switched Ethernet networks, while an improvement over hub based Ethernet, suffer from a number of issues:

They suffer from single points of failure. If any link fails some devices will be unable to communicate with other devices and if the link that fails is in a central location lots of users can be cut off from the resources they require.
It is possible to trick switches or hosts into sending data to a machine even if it's not intended for it (see switch vulnerabilities).
Large amounts of broadcast traffic, whether malicious, accidental, or simply a side effect of network size can flood slower links and/or systems.
- It is possible for any host to flood the network with broadcast traffic forming a denial of service attack against any hosts that run at the same or lower speed as the attacking device.
- As the network grows, normal broadcast traffic takes up an ever greater amount of bandwidth.
- If switches are not multicast aware, multicast traffic will end up treated like broadcast traffic due to being directed at a MAC with no associated port.
- If switches discover more MAC addresses than they can store (either through network size or through an attack) some addresses must inevitably be dropped and traffic to those addresses will be treated the same way as traffic to unknown addresses, that is essentially the same as broadcast traffic (this issue is known as failopen).
They suffer from bandwidth choke points where a lot of traffic is forced down a single link.

Some switches offer a variety of tools to combat these issues including:

Spanning-tree protocol to maintain the active links of the network as a tree while allowing physical loops for redundancy.
Various port protection features, as it is far more likely an attacker will be on an end system port than on a switch-switch link.
VLANs to keep different classes of users separate while using the same physical infrastructure.
Fast routing at higher levels to route between those VLANs.
Link aggregation to add bandwidth to overloaded links and to provide some measure of redundancy, although the links won't protect against switch failure because they connect the same pair of switches.

[edit] Autonegotiation and duplex modes

Main articles: Autonegotiation and Duplex mismatch

While the early coaxial cable based variants of Ethernet were half-duplex by design, all the common variants of twisted pair (10BASE-T, 100BASE-TX and 1000BASE-T) and fiber optic Ethernet provide separate channels for send and receive (full-duplex).
To allow use of hubs and for compatibility with existing variants of Ethernet they were originally implemented in a half-duplex manner with the transceiver detecting a collision if an attempt was made to transmit and receive simultaneously. However, if both ends of the link are not hubs, and the hardware supports it, the two channels can be split and used to make a full-duplex link.
In combination with the various speeds, this results in many different modes of operations (10BASE-T half duplex, 10BASE-T full duplex, 100BASE-TX half duplex, …) for Ethernet over twisted pair cable. In 1995, IEEE standard 802.3u (100BASE-TX) was released, allowing two network interfaces connected to each other to autonegotiate the best possible shared mode of operation. While implementation of autonegotiation is not required for a compliant 10BASE-T or 100BASE-TX Ethernet port, it is recommended as default behaviour by IEEE 802.3u. 1000BASE-T devices are required to implement autonegotiation in order to elect the clock master.
Ethernet contains a mechanism for detecting the speed but not the duplex setting of an Ethernet peer that did not use autonegotiation. when the remote does not negotiate An autonegotiating device assumes the remote device is a hub and defaults to half duplex. If the remote is, in fact a hub or a device operating in half duplex mode this works. But if remote is in full duplex mode, this generates a duplex mismatch. When two interfaces are connected and set to different duplex modes, the effect of the duplex mismatch is a network that works, but is much slower than its nominal speed. To avoid this, never set one end of a connection to a forced full-duplex setting and the other end to autonegotiation. Or better yet, never disable autonegotiation on any port. There are no disadvantages of keeping autonegotiation active on all devices.

[edit] Physical layer

This section does not cite any references or sources.
Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2008)

Main article: Ethernet physical layer

The first Ethernet networks, 10BASE5, used thick yellow cable with vampire taps as a shared medium (using CSMA/CD). Later, 10BASE2 Ethernet used thinner coaxial cable (with BNC connectors) as the shared CSMA/CD medium. The later StarLAN 1BASE5 and 10BASE-T used twisted pair connected to Ethernet hubs with 8P8C (RJ45) modular connectors.
Currently Ethernet has many varieties that vary both in speed and physical medium used. The most common forms used are 10BASE-T, 100BASE-TX, and 1000BASE-T. All three utilize Category 5 cables and 8P8C modular connectors. They run at 10 Mbit/s, 100 Mbit/s, and 1 Gbit/s, respectively.
Fiber optic variants of Ethernet are commonly used in structured cabling applications. These variants have also seen substantial penetration in enterprise datacenter applications, but are rarely seen connected to end user systems for cost/convenience reasons. Their advantages lie in performance, electrical isolation and distance (up to tens of kilometers with some versions). 10 gigabit Ethernet is becoming more popular in both enterprise and carrier networks, with development starting on 40 Gbit/s^[10]^[11] and 100 Gbit/s Ethernet.^[12] Metcalfe now believes commercial applications using terabit Ethernet may occur by 2015 though he says existing Ethernet standards may have to be overthrown to reach terabit Ethernet.^[13]
A data packet on the wire is called a frame and consists of just a long string of binary 0's and 1's. A frame viewed on the actual physical wire would show Preamble and Start Frame Delimiter, in addition to the other data. These are required by all physical hardware. However, they are not displayed by packet sniffing software because these bits are stripped away at OSI Layer 1 by the Ethernet adapter before being passed on to the OSI Layer 2 which is where packet sniffers collect their data from. There are OSI Physical Layer sniffers which can capture and display the Preamble and Start Frame but they are expensive and mainly used to detect physical related problems.
The table below shows the complete Ethernet frame, as transmitted, for the MTU of 1500 bytes (some implementations of gigabit Ethernet and higher speeds support larger jumbo frames). Note that the bit patterns in the preamble and start of frame delimiter are written as bit strings, with the first bit transmitted on the left (not as byte values, which in Ethernet are transmitted least significant bit first). This notation matches the one used in the IEEE 802.3 standard. One octet is eight bits of data (i.e., a byte on most modern computers).
10/100M transceiver chips (MII PHY) work with four bits (one nibble) at a time. Therefore the preamble will be 7 instances of 0101 + 0101, and the Start Frame Delimiter will be 0101 + 1101. 8-bit values are sent low 4-bit and then high 4-bit. 1000M transceiver chips (GMII) work with 8 bits at a time, and 10 Gbit/s (XGMII) PHY works with 32 bits at a time.

802.3 MAC Frame
Preamble	Start-of-Frame-Delimiter	MAC destination	MAC source	802.1Q header (optional)	Ethertype/Length	Payload (Data and padding)	CRC32	Interframe gap
7 octets of 10101010	1 octet of 10101011	6 octets	6 octets	(4 octets)	2 octets	46–1500 octets	4 octets	12 octets
		64–1522 octets
72–1530 octets
84–1542 octets

After a frame has been sent transmitters are required to transmit 12 octets of idle characters before transmitting the next frame.
From this table, we may calculate the efficiency and net bit rate for Ethernet:

Maximum efficiency is achieved with largest allowed payload size and is for untagged Ethernet packets and when 802.1Q VLAN tagging is used.
Net bit rate may be calculated from efficiency:

Maximum net bit rate for 100BASE-TX Ethernet without 802.1Q is 97.53 Mbit/s.

[edit] Ethernet frame types and the EtherType field

Main articles: Ethernet II framing and EtherType

There are several types of Ethernet frames:

The Ethernet Version 2 or Ethernet II frame, the so-called DIX frame (named after DEC, Intel, and Xerox); this is the most common today, as it is often used directly by the Internet Protocol.
Novell's non-standard variation of IEEE 802.3 ("raw 802.3 frame") without an IEEE 802.2 LLC header.
IEEE 802.2 LLC frame
IEEE 802.2 LLC/SNAP frame

In addition, all four Ethernet frames types may optionally contain a IEEE 802.1Q tag to identify what VLAN it belongs to and its IEEE 802.1p priority (quality of service). This encapsulation is defined in the IEEE 802.3ac specification and increases the maximum frame by 4 bytes to 1522 bytes.
The different frame types have different formats and MTU values, but can coexist on the same physical medium.

The most common Ethernet Frame format, type II

Versions 1.0 and 2.0 of the Digital/Intel/Xerox (DIX) Ethernet specification have a 16-bit sub-protocol label field called the EtherType. The new IEEE 802.3 Ethernet specification replaced that with a 16-bit length field, with the MAC header followed by an IEEE 802.2 logical link control (LLC) header. The maximum length of a frame was 1518 bytes for untagged (1522 for 802.1p or 802.1q tagged) classical Ethernet v2 and IEEE802.3 frames. The two formats were eventually unified by the convention that values of that field between 64 and 1522 indicated the use of the new 802.3 Ethernet format with a length field, while values of 1536 decimal (0600 hexadecimal) and greater indicated the use of the original DIX or Ethernet II frame format with an EtherType sub-protocol identifier.^[14] This convention allows software to determine whether a frame is an Ethernet II frame or an IEEE 802.3 frame, allowing the coexistence of both standards on the same physical medium. See also Jumbo Frames.
By examining the 802.2 LLC header, it is possible to determine whether it is followed by a SNAP (subnetwork access protocol) header. Some protocols, particularly those designed for the OSI networking stack, operate directly on top of 802.2 LLC, which provides both datagram and connection-oriented network services. The LLC header includes two additional eight-bit address fields, called service access points or SAPs in OSI terminology; when both source and destination SAP are set to the value 0xAA, the SNAP service is requested. The SNAP header allows EtherType values to be used with all IEEE 802 protocols, as well as supporting private protocol ID spaces. In IEEE 802.3x-1997, the IEEE Ethernet standard was changed to explicitly allow the use of the 16-bit field after the MAC addresses to be used as a length field or a type field.
Novell's "raw" 802.3 frame format was based on early IEEE 802.3 work. Novell used this as a starting point to create the first implementation of its own IPX Network Protocol over Ethernet. They did not use any LLC header but started the IPX packet directly after the length field. This does not conform to the IEEE 802.3 standard, but since IPX has always FF at the first two bytes (while in IEEE 802.2 LLC that pattern is theoretically possible but extremely unlikely), in practice this mostly coexists on the wire with other Ethernet implementations, with the notable exception of some early forms of DECnet which got confused by this.
Novell NetWare used this frame type by default until the mid nineties, and since Netware was very widespread back then, while IP was not, at some point in time most of the world's Ethernet traffic ran over "raw" 802.3 carrying IPX. Since Netware 4.10, Netware now defaults to IEEE 802.2 with LLC (Netware Frame Type Ethernet_802.2) when using IPX. (See "Ethernet Framing" in References for details.)
Mac OS uses 802.2/SNAP framing for the AppleTalk V2 protocol suite on Ethernet ("EtherTalk") and Ethernet II framing for TCP/IP.
The 802.2 variants of Ethernet are not in widespread use on common networks currently, with the exception of large corporate Netware installations that have not yet migrated to Netware over IP. In the past, many corporate networks supported 802.2 Ethernet to support transparent translating bridges between Ethernet and IEEE 802.5 Token Ring or FDDI networks. The most common framing type used today is Ethernet Version 2, as it is used by most Internet Protocol-based networks, with its EtherType set to 0x0800 for IPv4 and 0x86DD for IPv6.
There exists an Internet standard for encapsulating IP version 4 traffic in IEEE 802.2 frames with LLC/SNAP headers.^[15] It is almost never implemented on Ethernet (although it is used on FDDI and on token ring, IEEE 802.11, and other IEEE 802 networks). IP traffic cannot be encapsulated in IEEE 802.2 LLC frames without SNAP because, although there is an LLC protocol type for IP, there is no LLC protocol type for ARP. IP Version 6 can also be transmitted over Ethernet using IEEE 802.2 with LLC/SNAP, but, again, that's almost never used (although LLC/SNAP encapsulation of IPv6 is used on IEEE 802 networks).
The IEEE 802.1Q tag, if present, is placed between the Source Address and the EtherType or Length fields. The first two bytes of the tag are the Tag Protocol Identifier (TPID) value of 0x8100. This is located in the same place as the EtherType/Length field in untagged frames, so an EtherType value of 0x8100 means the frame is tagged, and the true EtherType/Length is located after the Q-tag. The TPID is followed by two bytes containing the Tag Control Information (TCI) (the IEEE 802.1p priority (quality of service) and VLAN id). The Q-tag is followed by the rest of the frame, using one of the types described above.

[edit] Runt frames

A runt frame is an Ethernet frame that is less than the IEEE 802.3 minimum length of 64 bytes. Possible causes are collision, underruns, bad network card or software.^[16]^[17]

[edit] Varieties of Ethernet

Main article: Ethernet physical layer

The Ethernet physical layer evolved over a considerable time span and encompasses quite a few physical media interfaces and several magnitudes of speed. The speed ranges from 1 Mbit/s to 10 Gbit/s in speed (higher speeds are under development)^{[citation needed]} while the physical medium can range from bulky coaxial cable to twisted pair to optical fiber. In general, network protocol stack software will work similarly on all varieties.

[edit] Related standards

Networking standards that are not part of the IEEE 802.3 Ethernet standard, but support the Ethernet frame format, and are capable of interoperating with it.
- LattisNet—A SynOptics pre-standard twisted-pair 10 Mbit/s variant.
- 100BaseVG—An early contender for 100 Mbit/s Ethernet. It runs over Category 3 cabling. Uses four pairs. Commercial failure.
- TIA 100BASE-SX—Promoted by the Telecommunications Industry Association. 100BASE-SX is an alternative implementation of 100 Mbit/s Ethernet over fiber; it is incompatible with the official 100BASE-FX standard. Its main feature is interoperability with 10BASE-FL, supporting autonegotiation between 10 Mbit/s and 100 Mbit/s operation – a feature lacking in the official standards due to the use of differing LED wavelengths. It is targeted at the installed base of 10 Mbit/s fiber network installations.
- TIA 1000BASE-TX—Promoted by the Telecommunications Industry Association, it was a commercial failure, and no products exist. 1000BASE-TX uses a simpler protocol than the official 1000BASE-T standard so the electronics can be cheaper, but requires Category 6 cabling.
- G.hn—A standard developed by ITU-T and promoted by HomeGrid Forum for high-speed (up to 1 Gbit/s) local area networks over existing home wiring (coaxial cables, power lines and phone lines). G.hn defines an Application Protocol Convergence (APC) layer that accepts Ethernet frames and encapsulates them into G.hn MSDUs.

Networking standards that do not use the Ethernet frame format but can still be connected to Ethernet using MAC-based bridging.
- 802.11—A standard for wireless local area networks (LANs), often paired with an Ethernet backbone.
- 802.16—A standard for wireless metropolitan area networks (MANs), including WiMAX
10BaseS—Ethernet over VDSL
Long Reach Ethernet
Avionics Full-Duplex Switched Ethernet
TTEthernet — Time-Triggered Ethernet for design of mixed-criticality embedded systems
Metro Ethernet

It has been observed that Ethernet traffic has self-similar properties, with important consequences for traffic engineering.^{[citation needed]}

[edit] See also

[edit] Notes

^ The experimental Ethernet described in the 1976 paper ran at 3 Mbit/s and had eight-bit destination and source address fields, so the original Ethernet addresses were not the MAC addresses they are today. By software convention, the 16 bits after the destination and source address fields specified a "packet type", but, as the paper says, "different protocols use disjoint sets of packet types". Thus the original packet types could vary within each different protocol, rather than the packet type in the current Ethernet standard which specifies the protocol being used.

http://en.wikipedia.org/wiki/Ethernet
06/09/10

Web Server

2010-06-09T14:52:00.000-04:00

A web server is a computer program that delivers (serves) content, such as web pages, using the Hypertext Transfer Protocol (HTTP), over the World Wide Web. The term web server can also refer to the computer or virtual machine running the program. In large commercial deployments, a server computer running a web server can be rack-mounted with other servers to operate a web farm.

[hide]

[edit] Overview

The primary function of a web server is to deliver web pages to clients. This means delivery of HTML documents and any additional content that may be included by a document, such as images, style sheets and JavaScripts.
A client, commonly a web browser or web crawler, initiates communication by making a request for a specific resource using HTTP and the server responds with the content of that resource, or an error message if unable to do so. The resource is typically a real file on the server's secondary memory, but this is not necessarily the case and depends on how the web server is implemented.
While the primary function is to serve content, a full implementation of HTTP also includes a way of receiving content from clients. This feature is used for submitting web forms, including uploading of files.
Many generic web servers also support server-side scripting, e.g., Apache HTTP Server and PHP. This means that the behaviour of the web server can be scripted in separate files, while the actual server software remains unchanged. Usually, this functionality is used to create HTML documents on-the-fly as opposed to return fixed documents. This is referred to as dynamic and static content respectively. The former is primarily used for retrieving and/or modifying information in databases. The latter is, however, typically much faster and easily cached.
Web servers are not always used for serving the world wide web, but they can also be found embedded in devices such as printers, routers, webcams and serving only a local network. The web server may then be used as a part of a system for monitoring and/or administrating the device in question. This usually means that no additional software has to be installed on the client computer, since a only a web browser is required (which by now is included with most operating systems).

[edit] History of web servers

The world's first web server.

In 1989 Tim Berners-Lee proposed to his employer CERN (European Organization for Nuclear Research) a new project, which had the goal of easing the exchange of information between scientists by using a hypertext system. As a result of the implementation of this project, in 1990 Berners-Lee wrote two programs:

a browser called WorldWideWeb;
the world's first web server, later known as CERN httpd, which ran on NeXTSTEP.

Between 1991 and 1994 the simplicity and effectiveness of early technologies used to surf and exchange data through the World Wide Web helped to port them to many different operating systems and spread their use among lots of different social groups of people, first in scientific organizations, then in universities and finally in industry.
In 1994 Tim Berners-Lee decided to constitute the World Wide Web Consortium (W3C) to regulate the further development of the many technologies involved (HTTP, HTML, etc.) through a standardization process.

[edit] Common features

Virtual hosting to serve many Web sites using one IP address.
Large file support to be able to serve files whose size is greater than 2 GB on 32 bit OS.
Bandwidth throttling to limit the speed of responses in order to not saturate the network and to be able to serve more clients.
Server-side scripting to generate dynamic Web pages, but still keeping Web server and Web site implementations separate from each other.

[edit] Path translation

Web servers are able to map the path component of a Uniform Resource Locator (URL) into:

a local file system resource (for static requests);
an internal or external program name (for dynamic requests).

For a static request the URL path specified by the client is relative to the Web server's root directory.
Consider the following URL as it would be requested by a client:

http://www.example.com/path/file.html

The client's user agent will translate it into a connection to www.example.com with the following HTTP 1.1 request:

GET /path/file.html HTTP/1.1
Host: www.example.com

The Web server on www.example.com will append the given path to the path of its root directory. On Unix machines, this is commonly /var/www. The result is the local file system resource:

/var/www/path/file.html

The Web server will then read the file, if it exists, and send a response to the client's Web browser. The response will describe the content of the file and contain the file itself.

[edit] Load limits

A Web server (program) has defined load limits, because it can handle only a limited number of concurrent client connections (usually between 2 and 80,000, by default between 500 and 1,000) per IP address (and TCP port) and it can serve only a certain maximum number of requests per second depending on:

its own settings;
the HTTP request type;
content origin (static or dynamic);
the fact that the served content is or is not cached;
the hardware and software limits of the OS where it is working.

When a Web server is near to or over its limits, it becomes unresponsive.

[edit] Kernel-mode and user-mode Web servers

A Web server can be either implemented into the OS kernel, or in user space (like other regular applications).
An in-kernel Web server (like TUX on GNU/Linux or Microsoft IIS on Windows) will usually work faster, because, as part of the system, it can directly use all the hardware resources it needs, such as non-paged memory, CPU time-slices, network adapters, or buffers.
Web servers that run in user-mode have to ask the system the permission to use more memory or more CPU resources. Not only do these requests to the kernel take time, but they are not always satisfied because the system reserves resources for its own usage and has the responsibility to share hardware resources with all the other running applications.
Also, applications cannot access the system's internal buffers, which causes useless buffer copies that create another handicap for user-mode web servers. As a consequence, the only way for a user-mode web server to match kernel-mode performance is to raise the quality of its code to much higher standards, similar to that of the code used in web servers that run in the kernel. This is a significant issue under Windows, where the user-mode overhead is about six times greater than that under Linux.^[1]

[edit] Overload causes

At any time Web servers can be overloaded because of:

Too much legitimate Web traffic. Thousands or even millions of clients connecting to the Web site in a short interval, e.g., Slashdot effect;
DDoS. Distributed Denial of Service attacks;
Computer worms that sometimes cause abnormal traffic because of millions of infected computers (not coordinated among them);
XSS viruses can cause high traffic because of millions of infected browsers and/or Web servers;
Internet Web robots. Traffic not filtered/limited on large Web sites with very few resources (bandwidth, etc.);
Internet (network) slowdowns, so that client requests are served more slowly and the number of connections increases so much that server limits are reached;
Web servers (computers) partial unavailability. This can happen because of required or urgent maintenance or upgrade, hardware or software failures, back-end (e.g., DB) failures, etc.; in these cases the remaining Web servers get too much traffic and become overloaded.

[edit] Overload symptoms

The symptoms of an overloaded Web server are:

requests are served with (possibly long) delays (from 1 second to a few hundred seconds);
500, 502, 503, 504 HTTP errors are returned to clients (sometimes also unrelated 404 error or even 408 error may be returned);
TCP connections are refused or reset (interrupted) before any content is sent to clients;
in very rare cases, only partial contents are sent (but this behavior may well be considered a bug, even if it usually depends on unavailable system resources).

[edit] Anti-overload techniques

To partially overcome above load limits and to prevent overload, most popular Web sites use common techniques like:

managing network traffic, by using:
- Firewalls to block unwanted traffic coming from bad IP sources or having bad patterns;
- HTTP traffic managers to drop, redirect or rewrite requests having bad HTTP patterns;
- Bandwidth management and traffic shaping, in order to smooth down peaks in network usage;
deploying Web cache techniques;
using different domain names to serve different (static and dynamic) content by separate Web servers, i.e.:
- ```
http://images.example.com
```
- ```
http://www.example.com
```
using different domain names and/or computers to separate big files from small and medium sized files; the idea is to be able to fully cache small and medium sized files and to efficiently serve big or huge (over 10 - 1000 MB) files by using different settings;
using many Web servers (programs) per computer, each one bound to its own network card and IP address;
using many Web servers (computers) that are grouped together so that they act or are seen as one big Web server, see also: Load balancer;
adding more hardware resources (i.e. RAM, disks) to each computer;
tuning OS parameters for hardware capabilities and usage;
using more efficient computer programs for Web servers, etc.;
using other workarounds, especially if dynamic content is involved.

[edit] Market structure

Market share of major Web servers

For more details on HTTP server programs, see Category:Web server software.

Given below is a list of top web server software vendors published in a Netcraft survey in January 2010.

Vendor	Product	Web Sites Hosted (millions)	Percent
Apache	Apache	111	54%
Microsoft	IIS	50	24%
Igor Sysoev	nginx	16	8%
Google	GWS	15	7%
lighttpd	lighttpd	1	0.46%

[edit] See also

[edit] References

^ High performance kernel mode Web server for Windows

[edit] External links

World Web Server Usage Statistics
RFC 2616, the Request for Comments document that defines the HTTP 1.1 protocol.
C64WEB.COM — Commodore 64 running as a Web server using Contiki

[hide] v • d • e Website management

Concepts	Drop registrar · Overselling · Web document · Web content · Web hosting service · Web server · Webmaster · Website governance

Web hosting control panels	Comparison of control panels · cPanel · DirectAdmin · Domain Technologie Control · H-Sphere · InterWorx · ISPConfig · ispCP · LxAdmin · Plesk · Usermin · Webmin

Domain name managers and registrars	Afilias · AusRegistry · CZ.NIC · CIRA · CNNIC · DENIC · DNS Belgium · Domainz · ENom · Go Daddy · Melbourne IT · Museum Domain Management Association · Name.com · Network Solutions · NeuStar · OLM.net · Register.com · Tucows · Web.com

Web content management system	Conference management system · Document management system · Wiki software · Weblog software

Retrieved from "http://en.wikipedia.org/wiki/Web_server"

http://en.wikipedia.org/wiki/Web_Server

06/06/10

What is a FTP

2010-06-08T08:03:00.002-04:00

Definitions of ftp on the Web:

use the file transfer protocol to transfer data from one computer to another; "You can FTP these data"
file transfer protocol: protocol that allows users to copy files between their local system and any system they can reach on the network
wordnetweb.princeton.edu/perl/webwn
(File Transfer Protocol) A very common method of moving files between two Internet sites. FTP is a way to login to another Internet site for the purposes of retrieving and/or sending files. ...
www.chicowebdesign.com/common-terms.php
(File Transfer Protocol) One of the most common methods for sending files between two computers.
www.avallo.com/page/webterms
A method to allow users and web servers to transfer files.
www.avhoster.com/glossary/index.php
Short for File Transfer Protocol. Webmasters can easily manage all their files by connected to their FTP.
www.enter2host.com/glossary.asp
Computer software that permits the exchange of information between computers.
www.graphicsquote.com/glossaryofterms.html
A way of transferring files (uploading and downloading) across the Internet. Most web sites are uploaded to the Internet by means of an FTP ...
www.rackspace.co.uk/rackspace-home/media-centre/resource-centre/glossary/
A method of transferring one or more files from one computer to another on a network or phone line.
www.conceptwebsites.com/SEO/common-terms.htm
File Transfer Protocol: A client-server protocol which allows a user on one computer to transfer files to and from another computer over a TCP/IP ...
www.astron.nl/aips++/docs/glossary/f.html
File Transfer Protocol. The Internet protocol defining how to download and upload files between a client and an FTP server. ...
www.top-10-hosting-reviews.com/Glossary.html
File Transfer Protocol. The most widely-used method of uploading created files from a local machine to a server.
www.webhostingsources.com/glossary.php
A protocol used to transfer files between two computers. Generally used over a TCP/IP-based network.
www.vpa.org.vn/english/Maritime_term/glossary8/f.htm
Enables users to copy files to or from other computers on the Internet.
www.primode.com/glossary.html
The TCP/IP standard, high-level protocol for transferring files from one machine to another. Usually implemented as applications level programs ...
www.nettedautomation.com/glossary_menue/glossary_f.html
http://www.google.com/search?hl=en&client=firefox-a&hs=ZoI&rls=org.mozilla:en-US:official&defl=en&q=define:ftp&sa=X&ei=SDEOTOD_GYT58AbPn-2oCQ&ved=0CBUQkAE
06/07/10

Google Adwords

2010-06-08T08:01:00.000-04:00

About Google AdWords

Though Google is not actually a pay per click search engine, Google does receive the most broad coverage of any search engine. While providing what some consider to be the best search results on the market, Google decided to produce the most sophisticated pay per click marketing program on the web, Google AdWords.

Where do Google AdWords Show?

Google AdWords are the portion of the search engine results page off to the right side of the Google search result page. Though these listings are more likely viewed than any other, the Google Adwords system is still economic in many terms when compared to Overture. Which network is more effective depends upon what industry you are in.
Google AdWords also has a large distribution network which includes AOL, Ask Jeeves, EarthLink, and many other sites (including a few of my own). Google offers a program called Google AdSense, which allows users to display AdWords ads on their web sites for a portion of the proceeds.

What Makes AdWords an Awesome Advertising System?

Google Adwords calculates an ad relevancy multiplier (based on consumer clickthrough rate). The click through rate used in the relevancy algorithm is determined by your 1,000 most recent ad displays on the Google website. Your effective bid price is maximum bid price * clickthrough rate.

A / B Testing with Google AdWords

You are allowed to make multiple campaigns for the same keyword and track conversion ratios and ad cost. You can either run two different ad creative or send the searches to different pages to A/B split test in real time.
Continually refining your ads through A/B testing will eventually drastically increase your profit margin.

Try Google AdWords

When you search Google AdWords will appear off to the right side of the page. This listing also appear on Earthlink, Iwon, Ask Jeeves, Go, and AOL!

Google AdWords Details
minimum CPC	various
cost to open an account	$5
promotional specials	none
monthly minimum	none
time to set up an account	fast
web reach	comprehensive
sign up for a Google AdWords Account

Similarities between Overture and Google AdWords

Overture has a program similar to AdSense called Content Match. This program distributes Overture ads near the content of popular sites. Overture is currently only making promotion partnerships with large web sites.
Overture offers regional advertising like AdWords does. The Overture Local Match product does not have a minimum monthly spend. Overture Local Match also does not even require you to have a website to participate. It does require you to have a physical address to participate.
Both Overture and AdWords have amazingly large distribution networks.
Both Overture and AdWords default to broad match ad listings. Using broad match search terms do not need to exactly match the keyword you are bidding on for your ad to show up.
Overture has a ROI / bid management tool which can help monitor and improve your listings.
Google AdWords and Overture both offer free ROI tracking tools.
Both Overture and Google AdWords have a negative keyword tool which prevents you from paying for clickthroughs on irrelevant terms. Good terms to cancel out are usually: cheap, free, download, cracks, mp3s, wallpapers.. the type of terms where it is obvious the searcher would not likely convert to a sale or perform the desired action.

Difference between Overture and Google AdWords

Overture is strictly price driven. Google AdWords is mathematically driven based on consumer driven relevancy. The AdWords price is a function of cost per click * ad relevancy (based on click through rate.)
Overture takes a few days to set up an account - Google is almost instant. (less than 5 minutes)
Overture allows for different biding on the different matching levels - Google will price them based upon what is best using some value at or less than your max price per click. To set up the different value ranges in Google you would have to set up a direct match at one value and a different account at a lesser value.
Overture Local Match also does not even require you to have a website to participate. It does require you to have a physical address to participate. Google AdWords does not require a physical address and does require a website.
Google AdSense ads can appear on smaller sites. Overture is extremely selective with its partners (other than when it partners with companies like Gator / Claria).
Google allows syndication to be turned on or off so that your ad can appear in front of just Google users, or AOL users too. Since Overture drives most their traffic through partner sites they do not have a feature that allows you to turn search partner syndication off.
Google only costs $5 to open an account. Overture costs $50 and has a $20 monthly minimum spend.
Google has automatic approval of all ads - and will list them as long as they follow the guidelines. Overture usually reviews most ads before showing them.

Google AdWords Professional Program

Google created the Google AdWords Professional Program to help certify SEM experts. The requirements to attain the professional status are

You have to pass a mulitple choice test. The test was not too hard and took about an hour. Google has a free study program which can help you learn about AdWords.
You have to follow their guidelines.
You have to spend at least $1,000 in a 90 day period between ads on your sites and clients sites. Febuary 17, 2005 will be the end of the 90 day period for those who signed up right away.

Google also allows you to link together up to 500 AdWords accounts and manage them from a single login via the Google Professional Program.

Suggestion for Google AdWords

Google AdWords is just about everything you could want in an advertising system. It is quick, responsive, offers free tracking, cheap to start, offers geotargeting, syndication of ads is optional...AWESOME.
Do not get in bidding wars for generic terms. Opt to bid on more specific terms.
Send people to targeted landing pages when possible.

Free Google AdWords Tool:

GoogEdit is a free downloadable tool which helps format your Google AdWords ads. It has many useful features such as number and phrase stripper. GoogEdit also wraps your AdWords ads in the various matching levels so that you can better track your traffic and conversions.

Google AdWords Conversion Tracking:

Google AdWords offers free cross platform conversion tracking.

Sign up for an AdWords Account

It is fast and easy to sign up for a Google Adwords account. If you are going to launch a large Adwords campaign you may want to consider reading Andrew Goodman's tips on Adwords ($69 report.)

Category:

large pay per click search engines

Window XP Security in the .NET Framework

2010-06-04T14:31:00.001-04:00

Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops, and media centers. It was first released in August 2001, and is currently one of the most popular versions of Windows. The name "XP" is short for "eXPerience."^[3]
Windows XP is the successor to both Windows 2000 and Windows Me, and is the first consumer-oriented operating system produced by Microsoft to be built on the Windows NT kernel and architecture. Windows XP was first released on October 25, 2001, and over 400 million copies were in use in January 2006, according to an estimate in that month by an IDC analyst.^[4] It was succeeded by Windows Vista, which was released to volume license customers on November 8, 2006, and worldwide to the general public on January 30, 2007. Direct OEM and retail sales of Windows XP ceased on June 30, 2008. Microsoft continued to sell XP through their System Builders (smaller OEMs who sell assembled computers) program until January 31, 2009.^[5]^[6] XP may continue to be available as these sources run through their inventory or by purchasing Windows Vista Ultimate or Business and then downgrading to Windows XP.^[7]^[8]
The most common editions of the operating system are Windows XP Home Edition, which is targeted at home users, and Windows XP Professional, which offers additional features such as support for Windows Server domains and two physical processors, and is targeted at power users, business and enterprise clients. Windows XP Media Center Edition has additional multimedia features enhancing the ability to record and watch TV shows, view DVD movies, and listen to music. Windows XP Tablet PC Edition is designed to run stylus applications built using the Tablet PC platform.
Windows XP was eventually released for two additional architectures, Windows XP 64-bit Edition for IA-64 (Itanium) processors and Windows XP Professional x64 Edition for x86-64. There is also Windows XP Embedded, a component version of the Windows XP Professional, and editions for specific markets such as Windows XP Starter Edition. By mid 2009, a manufacturer revealed the first Windows XP powered cellular telephone.^[9]
The NT-based versions of Windows, which are programmed in C, C++, Assembly^[10], are known for their improved stability and efficiency over the 9x versions of Microsoft Windows.^[11]^[12] Windows XP presents a significantly redesigned graphical user interface, a change Microsoft promoted as more user-friendly than previous versions of Windows. A new software management facility called Side-by-Side Assembly was introduced to ameliorate the "DLL hell" that plagues 9x versions of Windows.^[13]^[14] It is also the first version of Windows to use product activation to combat illegal copying, a restriction that did not sit well with some users and privacy advocates. Windows XP has also been criticized by some users for security vulnerabilities, tight integration of applications such as Internet Explorer 6 and Windows Media Player, and for aspects of its default user interface. Later versions with Service Pack 2, Service Pack 3, and Internet Explorer 8 addressed some of these concerns.
During development, the project was codenamed "Whistler", after Whistler, British Columbia, as many Microsoft employees skied at the Whistler-Blackcomb ski resort.^[15]
As of the end of April 2010, Windows XP is the most widely used operating system in the world with a 56.1% market share, having peaked at 76.1% in January 2007.^[16]

[edit] Editions

Main article: Windows XP editions

Diagram representing the main editions of Windows XP. It is based on the category of the edition (grey) and codebase (black arrow).

The two major editions are Windows XP Home Edition, designed for home users, and Windows XP Professional, designed for business and power-users. XP Professional contains advanced features that the average home user would not use. However, these features are not necessarily missing from XP Home. They are simply disabled, but are there and can become functional. These releases were made available at retail outlets that sell computer software, and were preinstalled on computers sold by major computer manufacturers. As of mid-2008, both editions continue to be sold. A third edition, called Windows XP Media Center Edition was introduced in 2002 and was updated every year until 2006 to incorporate new digital media, broadcast television and Media Center Extender capabilities. Unlike the Home and Professional edition, it was never made available for retail purchase, and was typically either sold through OEM channels, or was preinstalled on computers that were typically marketed as "media center PCs".
Two different 64-bit editions were made available, one designed specifically for Itanium-based workstations, which was introduced in 2001 around the same time as the Home and Professional editions, but was discontinued a few years later when vendors of Itanium hardware stopped selling workstation-class machines due to low sales. The other, called Windows XP Professional x64 Edition, supports the x86-64 extension of the Intel IA-32 architecture. x86-64 is implemented by AMD as "AMD64", found in AMD's Opteron and Athlon 64 chips, and implemented by Intel as "Intel 64" (formerly known as IA-32e and EM64T), found in Intel's Pentium 4 and later chips.
Windows XP Tablet PC Edition was produced for a class of specially designed notebook/laptop computers called tablet PCs. It is compatible with a pen-sensitive screen, supporting handwritten notes and portrait-oriented screens.

Internet Explorer 6 running in Windows XP Tablet PC Edition.

Microsoft also released Windows XP Embedded, an edition for specific consumer electronics, set-top boxes, kiosks/ATMs, medical devices, arcade video games, point-of-sale terminals, and Voice over Internet Protocol (VoIP) components. In July 2006, Microsoft released Windows Fundamentals for Legacy PCs, a thin client version of Windows XP Embedded which targets older machines (as early as the original Pentium). It is only available to Software Assurance customers. It is intended for corporate customers who would like to upgrade to Windows XP to take advantage of its security and management capabilities, but can't afford to purchase new hardware.

[edit] Editions for specific markets

Windows XP Starter Edition is a lower-cost edition of Windows XP available in Thailand, Indonesia, Russia, India, Colombia, Brazil, Argentina, Peru, Bolivia, Chile, Mexico, Ecuador, Uruguay and Venezuela. It is similar to Windows XP Home, but is limited to low-end hardware, can only run 3 programs at a time, and has some other features either removed or disabled by default. Each country's edition is also customized for that country, including desktop backgrounds of popular locations, localized help features for those who may not speak English, and other default settings designed for easier use than typical Windows XP installations. The Malaysian version, for example, contains a desktop background of the Kuala Lumpur skyline.^[17]
In March 2004, the European Commission fined Microsoft €497 million (US$603 million) and ordered the company to provide a version of Windows without Windows Media Player. The Commission concluded that Microsoft "broke European Union competition law by leveraging its near monopoly in the market for PC operating systems onto the markets for work group server operating systems and for media players". After unsuccessful appeals in 2004 and 2005, Microsoft reached an agreement with the Commission where it would release a court-compliant version, Windows XP Edition N. This version does not include the company's Windows Media Player but instead encourages users to pick and download their own media player. Microsoft wanted to call this version Reduced Media Edition, but EU regulators objected and suggested the Edition N name, with the N signifying "not with Media Player" for both Home and Professional editions of Windows XP. Because it is sold at the same price as the version with Windows Media Player included, Dell, Hewlett-Packard, Lenovo and Fujitsu Siemens have chosen not to stock the product. However, Dell did offer the operating system for a short time. Consumer interest has been low, with roughly 1,500 units shipped to OEMs, and no reported sales to consumers.^[18]^[19]^[20]^[21]
In December 2005, the Korean Fair Trade Commission ordered Microsoft to make available editions of Windows XP and Windows Server 2003 that do not contain Windows Media Player or Windows Messenger.^[22] Like the European Commission decision, this decision was based on the grounds that Microsoft had abused its dominant position in the market to push other products onto consumers. Unlike that decision, however, Microsoft was also forced to withdraw the non-compliant versions of Windows from the South Korean market. This decision resulted in Microsoft's releasing "K" and "KN" variants of the Home and Professional editions in August 2006.
That same year, Microsoft also released two additional editions of Windows XP Home Edition directed towards subscription-based and pay-as-you-go pricing models. These editions, released as part of Microsoft's FlexGo initiative, are used in conjunction with a hardware component to enforce time limitations on the usage of Windows. Its target market is emerging economies such as Brazil and Vietnam.^[23]

[edit] Languages

Windows XP is available in many languages.^[24] In addition, MUI packs and Language Interface Packs translating the user interface are also available for certain languages.^[25]^[26]

[edit] ATMs

Automated teller machine (ATM) vendors Wincor Nixdorf, NCR Corporation and Diebold Incorporated have all adopted Microsoft Windows XP as their migration path from OS/2. Wincor Nixdorf who has been pushing for standardization for many years, began shipping ATMs with Windows when they first arrived on the scene.
Diebold initially shipped XP Home Edition exclusively, but, following extensive pressure from customer banks to support a common operating system, switched to support XP Professional to match their primary competitor, NCR Corporation and Wincor Nixdorf.

[edit] New and updated features

This section does not cite any references or sources.
Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (August 2008)

Main article: Features new to Windows XP

Windows XP introduced several new features to the Windows line, including:

Faster start-up and hibernation sequences
The ability to discard a newer device driver in favor of the previous one (known as driver rollback), should a driver upgrade not produce desirable results
A new, arguably more user-friendly interface, including the framework for developing themes for the desktop environment
Fast user switching, which allows a user to save the current state and open applications of their desktop and allow another user to log on without losing that information
The ClearType font rendering mechanism, which is designed to improve text readability on liquid crystal display (LCD) and similar monitors
Remote Desktop functionality, which allows users to connect to a computer running Windows XP Pro from across a network or the Internet and access their applications, files, printers, and devices
Support for most DSL modems and IEEE 802.11 connections, as well as networking over FireWire, and Bluetooth.

[edit] User interface

**Windows XP themes**

Default Blue (Luna)	Windows Classic

XP Media Center	The new start menu design in the "Energy blue" theme.

The "task grouping" feature introduced in Windows XP.

Windows XP features a new task-based graphical user interface. The Start menu and Windows indexing service were redesigned and many visual effects were added, including:

A translucent blue selection rectangle in Explorer
Drop shadows for icon labels on the desktop
Task-based sidebars in Explorer windows ("common tasks")
The ability to group the taskbar buttons of the windows of one application into one button
The ability to lock the taskbar and other toolbars to prevent accidental changes
The highlighting of recently added programs on the Start menu
Shadows under menus (Windows 2000 had shadows under mouse pointers, but not menus)

Windows XP analyzes the performance impact of visual effects and uses this to determine whether to enable them, so as to prevent the new functionality from consuming excessive additional processing overhead. Users can further customize these settings.^[27] Some effects, such as alpha compositing (transparency and fading), are handled entirely by many newer video cards. However, if the video card is not capable of hardware alpha blending, performance can be substantially hurt, and Microsoft recommends the feature should be turned off manually.^[28] Windows XP adds the ability for Windows to use "Visual Styles" to change the user interface. However, visual styles must be cryptographically signed by Microsoft to run. Luna is the name of the new visual style that ships with Windows XP, and is enabled by default for machines with more than 64 MiB of RAM. Luna refers only to one particular visual style, not to all of the new user interface features of Windows XP as a whole. Some users "patch" the uxtheme.dll file that restricts the ability to use visual styles, created by the general public or the user, on Windows XP.^[29]
In addition to the included Windows XP themes, there is one previously unreleased theme with a dark blue taskbar and window bars similar to Windows Vista titled "Royale Noir" available for download, albeit unofficially.^[30] Microsoft officially released a modified version of this theme as the "Zune" theme, to celebrate the launch of its Zune portable media player in November 2006. The differences are only visual with a new glassy look along with a black taskbar instead of dark blue and an orange start button instead of green.^[31] Additionally, the Media Center "Energy Blue" theme, which was included in the Media Center editions, is also available to download for use on all Windows XP editions.^[32]
The default wallpaper, Bliss, is a BMP photograph of a landscape in the Napa Valley outside Napa, California,^[33] with rolling green hills and a blue sky with stratocumulus and cirrus clouds.
The Windows 2000 "classic" interface can be used instead if preferred. Several third party utilities exist that provide hundreds of different visual styles. Microsoft licensed technology from WindowBlinds creator Stardock to create its visual styles in XP.^{[citation needed]}

[edit] System requirements

Designed for Windows XP computer hardware logo

System requirements for Windows XP Home and Professional editions as follows:^[34]

	Minimum	Recommended
Processor	233 MHz^[1]	300 MHz or higher
Memory	64 MB RAM^[2]	128 MB RAM or higher
Video adapter and monitor	Super VGA (800 x 600) or higher resolution
Hard drive disk free space	1.5 GB or higher (additional 1.8 GB in Service Pack 2^[35] and additional 900 MB in Service Pack 3^[36])
Drives	CD-ROM drive or DVD drive
Input devices	Keyboard. Microsoft Mouse or compatible pointing device
Sound	Sound card. Speakers or headphones
^1 Even though this is Microsoft's stated minimum processor speed for Windows XP, it is possible to install and run the operating system on early IA-32 processors such as a P5 Pentium without MMX instructions.^[37] Windows XP is not compatible with processors older than Pentium (such as 486) because it requires CMPXCHG8B instructions. ^2 For many workloads that involve Web browsing, e-mail, and other activities, 64 MB of RAM will provide [the] user experience equivalent or superior to that of Windows Me running on the same hardware."^[38]

[edit] Service packs

Microsoft occasionally releases service packs for its Windows operating systems to fix problems and add features. Each service pack is a superset of all previous service packs and patches so that only the latest service pack needs to be installed, and also includes new revisions.^[39] However if you still have the earliest version of Win XP on Retail CD (without any service packs included), you will need to install SP1a or SP2, before SP3 can be installed. Older service packs need not be manually removed before application of the most recent one. Windows Update "normally" takes care of automatically removing unnecessary files.
The service pack details below only apply to the 32-bit editions. Windows XP Professional x64 Edition was based on Windows Server 2003 Service Pack 1 and claimed to be "SP1" in system properties from the initial release. It is updated by the same service packs and hotfixes as the x64 edition of Windows Server 2003.

[edit] Service Pack 1

Set Program Access and Defaults was added in Service Pack 1.

Service Pack 1 (SP1) for Windows XP was released on September 9, 2002. It contains post-RTM security fixes and hot-fixes, compatibility updates, optional .NET Framework support, enabling technologies for new devices such as Tablet PCs, and a new Windows Messenger 4.7 version. The most notable new features were USB 2.0 support and a Set Program Access and Defaults utility that aimed at hiding various middleware products. Users can control the default application for activities such as web browsing and instant messaging, as well as hide access to some of Microsoft's bundled programs. This utility was first brought into the older Windows 2000 operating system with its Service Pack 3. This Service Pack supported SATA and hard drives that were larger than 137GB (48-bit LBA support) by default. The Microsoft Java Virtual Machine, which was not in the RTM version, appeared in this Service Pack.^[40] Support for IPv6 was also introduced in this Service Pack.
On February 3, 2003, Microsoft released Service Pack 1a (SP1a). This release removed Microsoft's Java virtual machine as a result of a lawsuit with Sun Microsystems.^[41]

[edit] Service Pack 2

Windows Security Center was added in Service Pack 2.

Service Pack 2 (SP2) (codenamed "Springboard") was released on August 25, 2004^[42], with an emphasis on security. Unlike the previous service pack, SP2 added new functionality to Windows XP, such as WPA encryption compatibility and improved Wi-Fi support (with a wizard utility), a pop-up ad blocker for Internet Explorer 6, and Bluetooth support. The new welcome screen during the kernel boot removes the subtitles "Professional", "Home Edition" and "Embedded" since Microsoft introduced new Windows XP editions prior to the release of SP2. The green loading bar in Home Edition and the yellow one in Embedded were replaced with the blue bar, seen in Professional and other versions of Windows XP, making the boot-screen of operating systems resemble each other. Colors in other areas, such as Control Panel and the Help and Support tool, remained as before.
Service Pack 2 also added new security enhancements, which included a major revision to the included firewall that was renamed to Windows Firewall and became enabled by default, Data Execution Prevention, which can be weakly emulated,^{[clarification needed]} gains hardware support in the NX bit that can stop some forms of buffer overflow attacks. Also raw socket support is removed (which supposedly limits the damage done by zombie machines). Additionally, security-related improvements were made to e-mail and web browsing. Windows XP Service Pack 2 includes the Windows Security Center, which provides a general overview of security on the system, including the state of antivirus software, Windows Update, and the new Windows Firewall. Third-party anti-virus and firewall applications can interface with the new Security Center.^[43]

[edit] Service Pack 2b

In August 2006, Microsoft released updated installation media for Windows XP SP2 and Windows Server 2003 SP1 to contain a patch^[44] that requires ActiveX controls to require manual activation in accordance with a patent held by Eolas.^[45] Since then, the technology was licensed by Microsoft, and Service Pack 3 and later versions do not include this update.

[edit] Service Pack 2c

On August 10, 2007, Microsoft announced a minor update to Service Pack 2, called Service Pack 2c (SP2c).^[46] The update fixes the issue of the diminishing number of available product keys for Windows XP. This update was only available to system builders from their distributors in Windows XP Professional and Windows XP Professional N operating systems. SP2c was released in September 2007.^[47]

[edit] Service Pack 3

Windows XP Service Pack 3 (SP3) was released to manufacturing on April 21, 2008, and to the public via both the Microsoft Download Center and Windows Update on May 6, 2008.^[48]^[49]^[50]^[51]
It began being automatically pushed out to Automatic Update users on July 10, 2008.^[52] A feature set overview which details new features available separately as standalone updates to Windows XP, as well as backported features from Windows Vista has been posted by Microsoft.^[53] A total of 1,174 fixes have been included in SP3.^[54] Service Pack 3 can be installed on systems with Internet Explorer versions 6, 7 or 8.^[55] Internet Explorer 7 and 8 are not included as part of SP3.^[56]

[edit] New features in Service Pack 3

Turns black hole router detection on by default^[57]
Network Access Protection client
Group Policy support for IEEE 802.1X authentication for wired network adapters.^[58]
Credentials Security Service Provider^[59]
Descriptive Security options in Group Policy/Local Security Policy user interface
An updated version of the Microsoft Enhanced Cryptographic Provider Module (RSAENH) that is FIPS 140-2 certified (SHA-256, SHA-384 and SHA-512 algorithms)^[57]
Installing without requiring a product key during setup for retail and OEM versions

[edit] Previously released updates

Service Pack 3 also incorporated several previously released key updates for Windows XP, which were not included up to SP2 including:

Windows Imaging Component^[60]
IPSec Simple Policy Update for simplified creation and maintenance of IPSec filters^[61]
Background Intelligent Transfer Service (BITS) 2.5
MSXML 6.0 SP2 and XMLLite
Microsoft Management Console 3.0
Credential Roaming service (Digital Identity Management Service) update
Remote Desktop Protocol 6.1
Peer Name Resolution Protocol 2.1
Network Diagnostics update
WPA2 Update (KB893357)
Windows Script 5.7
Windows Installer 3.1 v2

Slipstreamed retail and OEM versions of Windows XP with SP3 can be installed and run with full functionality for 30 days without a product key, after which time the user will be prompted to enter a valid key and activate the installation. Volume license key (VLK) versions still require entering a product key before beginning installation.^[62]
XP SP3 is a cumulative update of all previous service packs for XP, the service pack installer checks HKLM\SYSTEM\CurrentControlSet\Control\Windows\CSDVersion registry key to see if has a value greater than or equal to 0x100, if it does it will allow the update to proceed, otherwise it will prompt to install either XP SP1 or SP2. Since SP1 is no longer available for full download, it would need to be downloaded using Windows Update. The other option is to manually change the registry key, in essence fool the installer into thinking SP1 is already installed.^[36]
However, it is possible to slipstream SP3 into the Windows XP setup files at any service pack level—including the original RTM version—without any errors or issues.^[63] Slipstreaming SP3 into Windows XP Media Center Edition 2005 is not supported.^[64]
Service Pack 3 contains updates to the operating system components of Windows XP Media Center Edition (MCE) and Windows XP Tablet PC Edition, and security updates for .NET Framework version 1.0, which is included in these Windows XP SKUs. However, it does not include update rollups for the Windows Media Center application in Windows XP MCE 2005.^[65] SP3 also omits security updates for Windows Media Player 10, although the player is included in Windows XP MCE 2005.^[65] The Address Bar DeskBand on the Taskbar is no longer included due to legal restrictions.^[66] It also removed the Energy Star logo from the ScreenSaver tab of the Display properties, leaving a very noticeable blank space next to the link to enter the Power Management control panel.

[edit] User complaints

There have been various complaints regarding Service Pack 3's installation and performance reported by many users, ranging from conflicts with other software such as Symantec and other security applications, to internet connectivity and reboot loops.^[67] ^[68]
Shortly after release, a large number of users with AMD processors reported that their PCs would not boot after installing Service Pack 3. The cause was established to be a result of OEMs who preinstalled (using Sysprep) a copy of Windows XP which had been created on a machine with an Intel processor. This resulted in the Intel SpeedStep driver (intelppm.sys) attempting to load on the AMD-based PC. Microsoft never supported this configuration.^[69]

[edit] Support lifecycle

Support for Windows XP without a service pack ended on September 30, 2004^[70] and support for Windows XP Service Pack 1 and 1a ended on October 10, 2006.^[71]^[72]
Windows XP Service Pack 2 will be retired on July 13, 2010, almost six years after its general availability.^[2] In accordance with Microsoft's posted timetable, the company stopped general licensing of Windows XP to OEMs and terminated retail sales of the operating system on June 30, 2008, 17 months after the release of Windows Vista.^[73]^[74] However, an exception was announced on April 3, 2008, for OEMs installing to ultra low-cost PCs (ULCPCs) until one year after the availability of Windows 7 (October 22, 2010)^[75]^[76]^[77]
On April 14, 2009, Windows XP and its family of operating systems were moved from Mainstream Support to the Extended Support phase as it marks the progression of the legacy operating system through the Microsoft Support Lifecycle Policy. During the Extended Support Phase, Microsoft will continue to provide security updates every month for Windows XP; however, free technical support, warranty claims and design changes are no longer being offered.
Only Software Assurance customers who still run Windows XP can enroll in the Extended Hotfix Support Agreement if they want to receive non-security related hotfixes. The enrollment offer for consumers ended on July 14, 2009.^{[citation needed]}
On April 8, 2014, all Windows XP support, including security updates and security-related hotfixes, will be terminated.^[2]

[edit] Criticism

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Main article: Criticism of Windows XP

[edit] Security issues

Windows XP has been criticized for its susceptibility to malware, viruses, trojan horses, and worms. Security issues are compounded by the fact that users, by default, receive an administrator account that provides unrestricted access to the underpinnings of the system. If the administrator's account is broken into, there is no limit to the control that can be asserted over the compromised PC.
Windows, with its large market share, has historically been a tempting target for virus creators. Security holes are often invisible until they are exploited, making preemptive action difficult. Microsoft has stated that the release of patches to fix security holes is often what causes the spread of exploits against those very same holes. Hackers exploit these holes by figuring out what problems the patches fix, and then proceed to launch attacks against unpatched systems. Microsoft recommends that all systems have automatic updates turned on to prevent a system from being attacked by an unpatched bug, but some business IT departments need to test updates before deployment across systems to predict compatibility issues with custom software and infrastructure. This deployment turn-around time also lengthens the time that systems are left unsecured in the event of a released software exploit.
When XP was released in 2001, it came with Internet Explorer 6, which is now insecure and outdated. Since February 2010, Microsoft has urged all users to upgrade to Internet Explorer 8, which has better security.

[edit] Integration of operating system features

In light of the United States v. Microsoft case which resulted in Microsoft being found liable for abusing its operating system monopoly to overwhelm competition in other markets, Windows XP has drawn fire for integrating user applications such as Windows Media Player and Windows Messenger into the operating system, as well as for its close ties to the Windows Live ID service.

[edit] Backward compatibility

Migrating from Windows 9x to XP can be an issue for users dependent upon MS-DOS. Although XP comes with the ability to run DOS programs in a virtual DOS machine, it still has trouble running many old DOS programs. This is largely because it is a Windows NT system and does not use DOS as a base OS, and that the Windows NT architecture is different from Windows 9x.^[78] Some DOS programs that cannot run natively on XP, notably programs that rely on direct access to hardware, can be run in emulators, such as DOSBox, or virtual machines, like VMware, Virtual PC, or VirtualBox.

[edit] Product activation and verification

[edit] Product activation

In an attempt to reduce piracy Windows XP introduced product activation. Activation requires the computer or the user to activate with Microsoft (either online or over the phone) within a certain amount of time in order to continue using the operating system. If the user's computer system ever changes — for example, if two or more relevant components of the computer itself are upgraded — Windows will return to the unactivated state and will need to be activated again within a defined grace period. If a user tries to reactivate too frequently, the system will refuse to activate online. The user must then contact Microsoft by telephone to obtain a new activation code.
However, activation only applies to retail and "system builder" (intended for use by small local PC builders) copies of Windows. "Royalty OEM" (used by large PC vendors) copies are instead locked to a special signature in the machine's BIOS (and will demand activation if moved to a system whose motherboard does not have the signature) and volume license copies do not require activation at all. Predictably, this led to pirates simply using volume license copies with volume license keys that were widely distributed on the Internet.

[edit] Product key testing

In addition to activation, Windows XP service packs will refuse to install on Windows XP systems with product keys known to be widely used in unauthorized installations. These product keys are either intended for use with one copy (for retail and system builder), for one OEM (for bios locked copies) or to one company (for volume license copies) and are included with the product. However a number of volume licence product keys (which as mentioned above avoid the need for activation) were posted on the Internet and were then used for a large number of unauthorized installations. The service packs contain a list of these keys and will not update copies of Windows XP that use them.
Microsoft developed a new key verification engine for Windows XP Service Pack 2 that could detect illicit keys, even those that had never been used before. After an outcry from security consultants who feared that denying security updates to illegal installations of Windows XP would have wide-ranging consequences even for legal owners, Microsoft elected to disable the new key verification engine. Service Pack 2 only checks for the same small list of commonly used keys as Service Pack 1. This means that while Service Pack 2 will not install on copies of Windows XP which use the older set of copied keys, those who use keys which have been posted more recently may be able to update their systems.

[edit] Windows Genuine Advantage

A Windows Genuine Advantage notification indicating a failed validation.

Main article: Windows Genuine Advantage

To try to curb piracy based on leaked or generated volume license keys, Microsoft introduced Windows Genuine Advantage (WGA). WGA comprises two parts, a verification tool which must be used to get certain downloads from Microsoft and a user notification system. WGA for Windows was followed by verification systems for Internet Explorer 7, Windows Media Player 11, Windows Defender, Microsoft Office 2007 and certain updates. In late 2007, Microsoft removed the WGA verification from the installer for Internet Explorer 7 saying that the purpose of the change was to make IE7 available to all Windows users.^[79]^[80]
If the license key is judged not genuine, it displays a nag screen at regular intervals asking the user to buy a license from Microsoft.^[81] In addition, the user's access to Microsoft Update is restricted to critical security updates, and as such, new versions of enhancements and other Microsoft products will no longer be able to be downloaded or installed. As of August 26, 2008, Microsoft has released a new WGA activation program that displays a plain black desktop background for computers failing validation. The background can be changed, but reverts after 1 hour.^[82]
Common criticisms of WGA have included its description as a "Critical Security Update", causing Automatic Updates to download it without user intervention on default settings, its behavior compared to spyware of "phoning home" to Microsoft every time the computer is connected to the Internet, the failure to inform end users what exactly WGA would do once installed (rectified by a 2006 update),^[83] the failure to provide a proper uninstallation method during beta testing (users were given manual removal instructions that did not work with the final build^[81]), and its sensitivity to hardware changes which cause repeated need for reactivation in the hands of some developers. Also if the user has no connection to the internet or a phone, it will be difficult to activate it normally.
Strictly speaking, neither the download nor the install of the Notifications is mandatory; the user can change their Automatic Update settings to allow them to choose what updates may be downloaded for installation. If the update is already downloaded, the user can choose not to accept the supplemental EULA provided for the Notifications. In both cases, the user can also request that the update not be presented again. Newer Critical Security Updates may still be installed with the update hidden. However this setting will only have effect on the existing version of Notifications, so it can appear again as a new version. As of 2006, Microsoft was involved in a class action lawsuit brought forth in California, on grounds that it violated the spyware laws in the state with its Windows Genuine Advantage Notifications program.^[84]

[edit] License and media types

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Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (August 2008)

There are three main types of Windows XP licenses: Retail, Volume (VLK), and Original Equipment Manufacturer (OEM). All three types of licenses are available for Windows XP Professional (32-bit and 64-bit). Windows XP Home Edition is limited to Retail and OEM licenses whereas Windows XP Media Center Edition and Windows XP Tablet PC Edition are exclusively available through VLK and OEM licenses.
Each type of license has a different installation CD. For customized or retail media, there is a small difference on each type of disc that will allow that installation disc to accept only one type of product key.
Only retail and volume licenses include support for end-user installation scenarios from Microsoft. OEM software is preinstalled on systems and is supported by the system manufacturer rather than Microsoft. The price of such software is lower. There are two important restrictions on OEM licenses: Microsoft does not offer technical support, and the license cannot be transferred to another computer. The cost of OEM software products bundled with systems is not disclosed by Microsoft nor by its partners, as each system manufacturer will define its own bundling price.
Microsoft recommends that system manufacturers have their systems tested, for a fee, as part of the Windows Quality Online Services (Winqual) which includes extensive testing so that no component will cause instability in the Windows operating system due to incompatibility with the Windows operating system or with other system components or their respective drivers. Having a system tested and approved will allow the manufacturer to bear the "Certified for Windows" logo sticker on the exterior of the system, and there are additional benefits for having a tested product. This includes the product's being listed on the Windows Marketplace. Because of the fees and extensive requirements, Microsoft acknowledges that smaller system manufacturers may not opt in to the program until they produce computer systems at a modest rate and on recurring designs.

[edit] Retail

Retail licenses, those purchased from a retail store in full packaging, are of two sub-types: "Upgrade" and "Full Purchase Product", often abbreviated by Microsoft as FPP. FPP licenses are transferable from one computer to another, provided the previous installation is removed from the old computer. Although upgrade licenses are also transferable, a user must have a previous version of Windows even on the new computer to which they are moving the installation. Retail licenses include installation support for end-users, provided directly by Microsoft.

[edit] Volume License

A Volume License is the license given to a software version sold to businesses under a direct purchase agreement with Microsoft, and is sold as an upgrade license only, meaning that a previous license must be available for each new volume license. Volume license versions of Windows XP use a Volume License Key (VLK) which is a product key that does not require Windows Product Activation. The term "Volume License Key" refers to the ability to use one product key for multiple systems, depending on the type of agreement. Since Windows XP Volume License versions do not require product activation, this led to leaked copies of VLK media and product keys from businesses leading to piracy of Windows XP quickly spreading across the Internet upon early release. Beginning with Service Pack 1, Microsoft's active attempts to search out and blacklist known pirated VLK product keys became well known due to the inability to install the service pack on a system with one of the blacklisted keys. Later, this led to the Windows Genuine Advantage program.

[edit] Original Equipment Manufacturer (OEM)

Original equipment manufacturer (OEM) licenses are preinstalled on, and sold with, pre-assembled computers from system manufacturers. There are two types of OEM product types — those used for "direct OEMs" (major name brands that buy through a direct contract with Microsoft and produce and brand their own media from a Microsoft "Gold Master Copy" by using an authorized Microsoft duplication partner), and those used for "system builders" (local computer shops that buy generic, unbranded kits through authorized Microsoft distributors). Direct OEM product keys will often not activate with system builder installation media because direct OEMs are now required by Microsoft to pre-activate their copies in the factory using their own internal mechanism before delivery to the customer. It is recommended that system builders also pre-activate their systems before delivery, but this is not mandatory.
OEM installations can be customized using the Microsoft OEM Preinstallation Kit with branding, logos, additional applications, optional services, alternate applications for certain Windows components, Internet Explorer links, and various other customizations. All OEM customers must include support and contact information for the initial installation of Windows because it is the responsibility for the OEM to support the Windows installation, and is not provided by Microsoft to the end-user. Direct OEMs must create their own media, but have the option of creating their own custom recovery solution, which may or may not be similar to a generic installation. OEMs may provide a recovery partition on the hard drive as the custom recovery solution rather than providing disc-based media with the computer.
Some end-users have found this to be a troublesome option, because in the event of an out-of-warranty hard drive failure, they may not have access to any installation media in order to reinstall Windows onto a new hard drive. System builders are not allowed the option to create a custom recovery CD/DVD media. The only deliverable media available for a system builder to give to the end-user is the unbranded OEM system builder hologram media kit. Because of this, when end-users reformat their hard drives and re-install from the installation media, they lose all the custom branding and support information that the system builder would have included.
As a supplemental recovery method to a CD/DVD-based installation, a system builder may employ a fully customized recovery solution on the hard drive. Whether utilizing a recovery partition or not, a system builder must still include the original generic OEM system builder hologram CD/DVD media kit. OEM licenses are not transferable from one computer to another. Every computer sold/resold with an OEM license must include all of the original installation media or recovery solution, documentation, Certificate of Authenticity, and product key sticker with the sale. Microsoft requires that all OEM system manufacturers include as part of the configuration the Windows Out-of-Box Experience (OOBE), which is the initial setup wizard encountered the first time Windows boots up. It is also required that value-added resellers (VAR's), retailers, and general resellers not tamper with the OEM's customized OOBE mechanism unless under permission by the OEM, and it is a recommended configuration for systems that are privately resold so that a customer will have a like-new computer experience upon first boot-up.
OEM licenses are to be installed by professional system manufacturers only. Under Microsoft's OEM License Agreement, they are not to be sold to end-users under any circumstance, and are to be preinstalled on a computer using the OEM Preinstallation Kit (OPK) before shipment to the customer, and must include at the very least the manufacturer's support contact information. They are, therefore, designed for installation only on a single computer and are not transferable, even if the original computer is no longer in use. This is not usually an issue for users who purchase new computer systems, because most pre-assembled systems ship with a preinstalled operating system. There are few circumstances where Microsoft will allow the transfer of an OEM license from one non-functioning system to another, but the OEM System Builder License Agreement (SBLA), as well as the OEM End User License Agreement (EULA) do not contain any allowance for this, so it is entirely up to Microsoft's discretion, depending on the situation.^[85]

[edit] Non-use by end user

In the event that an end user decides that they do not wish to use a preinstalled version of Windows, Microsoft's End User License Agreement (EULA) provides that the software may be returned to the OEM for a refund.^[86] Despite refusal of some manufacturers to honour the entitlement it has been enforced by courts in some countries.^[87]^[88]

^{http://en.wikipedia.org/wiki/Windows_XP}
^06/04/10

.Net Framework 4

2010-06-04T14:24:00.002-04:00

The Microsoft .NET Framework is a software framework that can be installed on computers running Microsoft Windows operating systems. It includes a large library of coded solutions to common programming problems and a virtual machine that manages the execution of programs written specifically for the framework. The .NET framework supports multiple programming languages in a manner that allows language interoperability, whereby each language can utilize code written in other languages; in particular, the .NET library is available to all the programming languages that .NET encompasses. The .NET Framework is a Microsoft offering and is intended to be used by most new applications created for the Windows platform.
The framework's Base Class Library provides a large range of features including user interface, data access, database connectivity, cryptography, web application development, numeric algorithms, and network communications. The class library is used by programmers, who combine it with their own code to produce applications.
Programs written for the .NET Framework execute in a software environment that manages the program's runtime requirements. Also part of the .NET Framework, this runtime environment is known as the Common Language Runtime (CLR). The CLR provides the appearance of an application virtual machine so that programmers need not consider the capabilities of the specific CPU that will execute the program. The CLR also provides other important services such as security, memory management, and exception handling. The class library and the CLR together constitute the .NET Framework.
Version 3.0 of the .NET Framework is included with Windows Server 2008 and Windows Vista. Version 3.5 is included with Windows 7, and can also be installed on Windows XP and the Windows Server 2003 family of operating systems.^[2] Version 4 of the framework was released as a public beta on 20 May 2009.^[3] In February 2010, Microsoft released a .NET Framework 4 release candidate.^[4] On April 12, 2010, the final version of the .NET Framework 4 was released.
The .NET Framework family also includes two versions for mobile or embedded device use. A reduced version of the framework, the .NET Compact Framework, is available on Windows CE platforms, including Windows Mobile devices such as smartphones. Additionally, the .NET Micro Framework is targeted at severely resource constrained devices.

[edit] Principal design features

Interoperability: Because interaction between new and older applications is commonly required, the .NET Framework provides means to access functionality that is implemented in programs that execute outside the .NET environment. Access to COM components is provided in the System.Runtime.InteropServices and System.EnterpriseServices namespaces of the framework; access to other functionality is provided using the P/Invoke feature.
Common Runtime Engine: The Common Language Runtime (CLR) is the virtual machine component of the .NET framework. All .NET programs execute under the supervision of the CLR, guaranteeing certain properties and behaviors in the areas of memory management, security, and exception handling.
Language Independence: The .NET Framework introduces a Common Type System, or CTS. The CTS specification defines all possible datatypes and programming constructs supported by the CLR and how they may or may not interact with each other conforming to the Common Language Infrastructure (CLI) specification. Because of this feature, the .NET Framework supports the exchange of types and object instances between libraries and applications written using any conforming .NET language.
Base Class Library: The Base Class Library (BCL), part of the Framework Class Library (FCL), is a library of functionality available to all languages using the .NET Framework. The BCL provides classes which encapsulate a number of common functions, including file reading and writing, graphic rendering, database interaction, XML document manipulation and so on.
Simplified Deployment: The .NET framework includes design features and tools that help manage the installation of computer software to ensure that it does not interfere with previously installed software, and that it conforms to security requirements.
Security: The design is meant to address some of the vulnerabilities, such as buffer overflows, that have been exploited by malicious software. Additionally, .NET provides a common security model for all applications.
Portability: The design of the .NET Framework allows it to theoretically be platform agnostic, and thus cross-platform compatible. That is, a program written to use the framework should run without change on any type of system for which the framework is implemented. While Microsoft has never implemented the full framework on any system except Microsoft Windows, the framework is engineered to be platform agnostic,^[5] and cross-platform implementations are available for other operating systems (see Silverlight and the Alternative implementations section below). Microsoft submitted the specifications for the Common Language Infrastructure (which includes the core class libraries, Common Type System, and the Common Intermediate Language),^[6]^[7]^[8] the C# language,^[9] and the C++/CLI language^[10] to both ECMA and the ISO, making them available as open standards. This makes it possible for third parties to create compatible implementations of the framework and its languages on other platforms.

[edit] Architecture

Visual overview of the Common Language Infrastructure (CLI)

[edit] Common Language Infrastructure (CLI)

Main article: Common Language Infrastructure

The purpose of the Common Language Infrastructure, or CLI, is to provide a language-neutral platform for application development and execution, including functions for exception handling, garbage collection, security, and interoperability. By implementing the core aspects of the .NET Framework within the scope of the CLR, this functionality will not be tied to a single language but will be available across the many languages supported by the framework. Microsoft's implementation of the CLI is called the Common Language Runtime, or CLR.

[edit] Assemblies

Main article: .NET assembly

The CIL code is housed in .NET assemblies. As mandated by specification, assemblies are stored in the Portable Executable (PE) format, common on the Windows platform for all DLL and EXE files. The assembly consists of one or more files, one of which must contain the manifest, which has the metadata for the assembly. The complete name of an assembly (not to be confused with the filename on disk) contains its simple text name, version number, culture, and public key token. The public key token is a unique hash generated when the assembly is compiled, thus two assemblies with the same public key token are guaranteed to be identical from the point of view of the framework. A private key can also be specified known only to the creator of the assembly and can be used for strong naming and to guarantee that the assembly is from the same author when a new version of the assembly is compiled (required to add an assembly to the Global Assembly Cache).

[edit] Metadata

Main article: .NET metadata

All CIL is self-describing through .NET metadata. The CLR checks the metadata to ensure that the correct method is called. Metadata is usually generated by language compilers but developers can create their own metadata through custom attributes. Metadata contains information about the assembly, and is also used to implement the reflective programming capabilities of .NET Framework.

[edit] Security

.NET has its own security mechanism with two general features: Code Access Security (CAS), and validation and verification. Code Access Security is based on evidence that is associated with a specific assembly. Typically the evidence is the source of the assembly (whether it is installed on the local machine or has been downloaded from the intranet or Internet). Code Access Security uses evidence to determine the permissions granted to the code. Other code can demand that calling code is granted a specified permission. The demand causes the CLR to perform a call stack walk: every assembly of each method in the call stack is checked for the required permission; if any assembly is not granted the permission a security exception is thrown.
When an assembly is loaded the CLR performs various tests. Two such tests are validation and verification. During validation the CLR checks that the assembly contains valid metadata and CIL, and whether the internal tables are correct. Verification is not so exact. The verification mechanism checks to see if the code does anything that is 'unsafe'. The algorithm used is quite conservative; hence occasionally code that is 'safe' does not pass. Unsafe code will only be executed if the assembly has the 'skip verification' permission, which generally means code that is installed on the local machine.
.NET Framework uses AppDomains as a mechanism for isolating code running in a process. AppDomains can be created and code loaded into or unloaded from them independent of other AppDomains. This helps increase the fault tolerance of the application, as faults or crashes in one AppDomains do not affect rest of the application. AppDomains can also be configured independently with different security privileges. This can help increase the security of the application by isolating potentially unsafe code. The developer, however, has to split the application into subdomains; it is not done by the CLR.

[edit] Class library

Namespaces in the BCL^[11]
System
System. CodeDom
System. Collections
System. Diagnostics
System. Globalization
System. IO
System. Resources
System. Text
System. Text.RegularExpressions

The .NET Framework includes a set of standard class libraries. The class library is organized in a hierarchy of namespaces. Most of the built in APIs are part of either System.* or Microsoft.* namespaces. These class libraries implement a large number of common functions, such as file reading and writing, graphic rendering, database interaction, and XML document manipulation, among others. The .NET class libraries are available to all CLI compliant languages. The .NET Framework class library is divided into two parts: the Base Class Library and the Framework Class Library.
The Base Class Library (BCL) includes a small subset of the entire class library and is the core set of classes that serve as the basic API of the Common Language Runtime.^[11] The classes in mscorlib.dll and some of the classes in System.dll and System.core.dll are considered to be a part of the BCL. The BCL classes are available in both .NET Framework as well as its alternative implementations including .NET Compact Framework, Microsoft Silverlight and Mono.
The Framework Class Library (FCL) is a superset of the BCL classes and refers to the entire class library that ships with .NET Framework. It includes an expanded set of libraries, including Windows Forms, ADO.NET, ASP.NET, Language Integrated Query, Windows Presentation Foundation, Windows Communication Foundation among others. The FCL is much larger in scope than standard libraries for languages like C++, and comparable in scope to the standard libraries of Java.

[edit] Memory management

The .NET Framework CLR frees the developer from the burden of managing memory (allocating and freeing up when done); instead it does the memory management itself. To this end, the memory allocated to instantiations of .NET types (objects) is done contiguously^[12] from the managed heap, a pool of memory managed by the CLR. As long as there exists a reference to an object, which might be either a direct reference to an object or via a graph of objects, the object is considered to be in use by the CLR. When there is no reference to an object, and it cannot be reached or used, it becomes garbage. However, it still holds on to the memory allocated to it. .NET Framework includes a garbage collector which runs periodically, on a separate thread from the application's thread, that enumerates all the unusable objects and reclaims the memory allocated to them.
The .NET Garbage Collector (GC) is a non-deterministic, compacting, mark-and-sweep garbage collector. The GC runs only when a certain amount of memory has been used or there is enough pressure for memory on the system. Since it is not guaranteed when the conditions to reclaim memory are reached, the GC runs are non-deterministic. Each .NET application has a set of roots, which are pointers to objects on the managed heap (managed objects). These include references to static objects and objects defined as local variables or method parameters currently in scope, as well as objects referred to by CPU registers.^[12] When the GC runs, it pauses the application, and for each object referred to in the root, it recursively enumerates all the objects reachable from the root objects and marks them as reachable. It uses .NET metadata and reflection to discover the objects encapsulated by an object, and then recursively walk them. It then enumerates all the objects on the heap (which were initially allocated contiguously) using reflection. All objects not marked as reachable are garbage.^[12] This is the mark phase.^[13] Since the memory held by garbage is not of any consequence, it is considered free space. However, this leaves chunks of free space between objects which were initially contiguous. The objects are then compacted together to make used memory contiguous again.^[12]^[13] Any reference to an object invalidated by moving the object is updated to reflect the new location by the GC.^[13] The application is resumed after the garbage collection is over.
The GC used by .NET Framework is actually generational.^[14] Objects are assigned a generation; newly created objects belong to Generation 0. The objects that survive a garbage collection are tagged as Generation 1, and the Generation 1 objects that survive another collection are Generation 2 objects. The .NET Framework uses up to Generation 2 objects.^[14] Higher generation objects are garbage collected less frequently than lower generation objects. This helps increase the efficiency of garbage collection, as older objects tend to have a larger lifetime than newer objects.^[14] Thus, by removing older (and thus more likely to survive a collection) objects from the scope of a collection run, fewer objects need to be checked and compacted.^[14]

[edit] Standardization and licensing

In August 2000, Microsoft, Hewlett-Packard, and Intel worked to standardize CLI and the C# programming language. By December 2001, both were ratified ECMA standards (ECMA 335 and ECMA 334). ISO followed in April 2003 - the current version of the ISO standards are ISO/IEC 23271:2006 and ISO/IEC 23270:2006.^[15]^[16]
While Microsoft and their partners hold patents^{[citation needed]} for the CLI and C#, ECMA and ISO require that all patents essential to implementation be made available under "reasonable and non-discriminatory terms". In addition to meeting these terms, the companies have agreed to make the patents available royalty-free.^{[citation needed]}
However, this does not apply for the part of the .NET Framework which is not covered by the ECMA/ISO standard, which includes Windows Forms, ADO.NET, and ASP.NET. Patents that Microsoft holds^{[citation needed]} in these areas may deter non-Microsoft implementations of the full framework.^[17]
On 3 October 2007, Microsoft announced that much of the source code for the .NET Framework Base Class Library (including ASP.NET, ADO.NET, and Windows Presentation Foundation) was to have been made available with the final release of Visual Studio 2008 towards the end of 2007 under the shared source Microsoft Reference License.^[1] The source code for other libraries including Windows Communication Foundation (WCF), Windows Workflow Foundation (WF), and Language Integrated Query (LINQ) were to be added in future releases. Being released under the non Open-source Microsoft Reference License means this source code is made available for debugging purpose only, primarily to support integrated debugging of the BCL in Visual Studio.

[edit] Versions

Microsoft started development on the .NET Framework in the late 1990s originally under the name of Next Generation Windows Services (NGWS). By late 2000 the first beta versions of .NET 1.0 were released.^[18]

The .NET Framework stack.

Version	Version Number	Release Date	Visual Studio	Default in Windows
1.0	1.0.3705.0	2002-02-13	Visual Studio .NET
1.1	1.1.4322.573	2003-04-24	Visual Studio .NET 2003	Windows Server 2003
2.0	2.0.50727.42	2005-11-07	Visual Studio 2005
3.0	3.0.4506.30	2006-11-06		Windows Vista, Windows Server 2008
3.5	3.5.21022.8	2007-11-19	Visual Studio 2008	Windows 7, Windows Server 2008 R2
4.0	4.0.30319.1	2010-04-12	Visual Studio 2010

A more complete listing of the releases of the .NET Framework may be found on the .NET Framework version list.

[edit] .NET Framework 1.0

The old .NET Framework logo

This is the first release of the .NET Framework, released on 13 February 2002 and available for Windows 98, Me, NT 4.0, 2000, and XP. Mainstream support by Microsoft for this version ended 10 July 2007, and extended support ended 14 July 2009.^[19]

[edit] .NET Framework 1.1

This is the first major .NET Framework upgrade. It is available on its own as a redistributable package or in a software development kit, and was published on 3 April 2003. It is also part of the second release of Microsoft Visual Studio .NET (released as Visual Studio .NET 2003). This is the first version of the .NET Framework to be included as part of the Windows operating system, shipping with Windows Server 2003. Mainstream support for .NET Framework 1.1 ended on 14 October 2008, and extended support ends on 8 October 2013. Since .NET 1.1 is a component of Windows Server 2003, extended support for .NET 1.1 on Server 2003 will run out with that of the OS - currently 14 July 2015.

[edit] Changes in 1.1 on comparison with 1.0

Built-in support for mobile ASP.NET controls. Previously available as an add-on for .NET Framework, now part of the framework.
Security changes - enable Windows Forms assemblies to execute in a semi-trusted manner from the Internet, and enable Code Access Security in ASP.NET applications.
Built-in support for ODBC and Oracle databases. Previously available as an add-on for .NET Framework 1.0, now part of the framework.
.NET Compact Framework - a version of the .NET Framework for small devices.
Internet Protocol version 6 (IPv6) support.
Numerous API changes.

[edit] .NET Framework 2.0

Released with Visual Studio 2005, Microsoft SQL Server 2005, and BizTalk 2006.

The 2.0 Redistributable Package can be downloaded for free from Microsoft, and was published on 22 January 2006.
The 2.0 Software Development Kit (SDK) can be downloaded for free from Microsoft.
It is included as part of Visual Studio 2005 and Microsoft SQL Server 2005.
Version 2.0 without any Service Pack is the last version with support for Windows 98 and Windows Me. Version 2.0 with Service Pack 2 is the last version with official support for Windows 2000 although there have been some unofficial workarounds published online to use a subset of the functionality from Version 3.5 in Windows 2000.^[20] Version 2.0 with Service Pack 2 requires Windows 2000 with SP4 plus KB835732 or KB891861 update, Windows XP with SP2 or later and Windows Installer 3.1 (KB893803-v2)
It shipped with Windows Server 2003 R2 (not installed by default).

[edit] Changes in 2.0 in comparison with 1.1

Generics
Language support for generics built directly into the .NET CLR.
Full 64-bit support for both the x64 and the IA64 hardware platforms.
Numerous API changes.
SQL Server integration - .Net 2.0, VS 2005, and SQL Server 2005 are all tied together. This means that instead of using T-SQL, one can build stored procedures and triggers in any of the .NET-compatible languages.
A new hosting API for native applications wishing to host an instance of the .NET runtime. The new API gives a fine grain control on the behavior of the runtime with regards to multithreading, memory allocation, assembly loading and more (detailed reference). It was initially developed to efficiently host the runtime in Microsoft SQL Server, which implements its own scheduler and memory manager.
Many additional and improved ASP.NET web controls.
New data controls with declarative data binding.
New personalization features for ASP.NET, such as support for themes, skins and webparts.
.NET Micro Framework - a version of the .NET Framework related to the Smart Personal Objects Technology initiative.
Partial classes
Nullable types
Anonymous methods
Iterators
Data tables

[edit] .NET Framework 3.0

.NET Framework 3.0, formerly called WinFX,^[21] was released on 21 November 2006. It includes a new set of managed code APIs that are an integral part of Windows Vista and Windows Server 2008 operating systems. It is also available for Windows XP SP2 and Windows Server 2003 as a download. There are no major architectural changes included with this release; .NET Framework 3.0 uses the Common Language Runtime of .NET Framework 2.0.^[22] Unlike the previous major .NET releases there was no .NET Compact Framework release made as a counterpart of this version.
.NET Framework 3.0 consists of four major new components:

Windows Presentation Foundation (WPF), formerly code-named Avalon; a new user interface subsystem and API based on XML and vector graphics, which uses 3D computer graphics hardware and Direct3D technologies. See WPF SDK for developer articles and documentation on WPF.
Windows Communication Foundation (WCF), formerly code-named Indigo; a service-oriented messaging system which allows programs to interoperate locally or remotely similar to web services.
Windows Workflow Foundation (WF) allows for building of task automation and integrated transactions using workflows.
Windows CardSpace, formerly code-named InfoCard; a software component which securely stores a person's digital identities and provides a unified interface for choosing the identity for a particular transaction, such as logging in to a website.

[edit] .NET Framework 3.5

Version 3.5 of the .NET Framework was released on 19 November 2007, but it is not included with Windows Server 2008. As with .NET Framework 3.0, version 3.5 uses the CLR of version 2.0. In addition, it installs .NET Framework 2.0 SP1, (installs .NET Framework 2.0 SP2 with 3.5 SP1) and .NET Framework 3.0 SP1 (installs .NET Framework 3.0 SP2 with 3.5 SP1), which adds some methods and properties to the BCL classes in version 2.0 which are required for version 3.5 features such as Language Integrated Query (LINQ). These changes do not affect applications written for version 2.0, however.^[23]
As with previous versions, a new .NET Compact Framework 3.5 was released in tandem with this update in order to provide support for additional features on Windows Mobile and Windows Embedded CE devices.
The source code of the Base Class Library in this version has been partially released (for debugging reference only) under the Microsoft Reference Source License.^[1]

[edit] Changes since version 3.0

New language features in C# 3.0 and VB.NET 9.0 compiler
Adds support for expression trees and lambda methods
Extension methods
Expression trees to represent high-level source code at runtime.^[24]
Anonymous types with static type inference
Language Integrated Query (LINQ) along with its various providers
- LINQ to Objects
- LINQ to XML
- LINQ to SQL
Paging support for ADO.NET
ADO.NET synchronization API to synchronize local caches and server side datastores
Asynchronous network I/O API.^[24]
Peer-to-peer networking stack, including a managed PNRP resolver^[25]
Managed wrappers for Windows Management Instrumentation and Active Directory APIs^[26]
Enhanced WCF and WF runtimes, which let WCF work with POX and JSON data, and also expose WF workflows as WCF services.^[27] WCF services can be made stateful using the WF persistence model.^[24]
Support for HTTP pipelining and syndication feeds.^[27]
ASP.NET AJAX is included.

[edit] Service Pack 1

The .NET Framework 3.5 Service Pack 1 was released on 11 August 2008. This release adds new functionality and provides performance improvements under certain conditions,^[28] especially with WPF where 20-45% improvements are expected. Two new data service components have been added, the ADO.NET Entity Framework and ADO.NET Data Services. Two new assemblies for web development, System.Web.Abstraction and System.Web.Routing, have been added; these are used in the ASP.NET MVC Framework and, reportedly, will be utilized in the future release of ASP.NET Forms applications. Service Pack 1 is included with SQL Server 2008 and Visual Studio 2008 Service Pack 1.It also featured a new set of controls called "Visual Basic Power Packs" which brought back Visual Basic controls such as "Line" and "Shape".

[edit] .NET Framework 3.5 SP1 Client Profile

For the .NET Framework 3.5 SP1 there is also a new variant of the .NET Framework, called the ".NET Framework Client Profile", which at 28 MB is significantly smaller than the full framework and only installs components that are the most relevant to desktop applications.^[29] However, the Client Profile amounts to this size only if using the online installer on Windows XP SP2 when no other .NET Frameworks are installed. When using the off-line installer or any other OS, the download size is still 250 MB.^[30]

[edit] .NET Framework 4

Microsoft announced the .NET Framework 4 on 29 September 2008. The Public Beta was released on 20 May 2009.^[3] Some focuses of this release are:

Parallel Extensions to improve support for parallel computing, which target multi-core or distributed systems.^[31] To this end, they plan to include technologies like PLINQ (Parallel LINQ),^[32] a parallel implementation of the LINQ engine, and Task Parallel Library, which exposes parallel constructs via method calls.^[33]
New Visual Basic .NET and C# language features, such as statement lambdas, implicit line continuations, dynamic dispatch, named parameters, and optional parameters.
Full support for IronPython, IronRuby, and F#.^[34]
Support for a subset of the .NET Framework and ASP.NET with the "Server Core" variant of Windows Server 2008 R2.^[35]
Support for Code Contracts.
Inclusion of the Oslo modelling platform, along with the M programming language.^[36]
Inclusion of new types to work with arbitrary-precision arithmetic (System.Numerics.BigInteger) and complex numbers (System.Numerics.Complex).

On 28 July 2009, a second release of the .NET Framework 4 beta was made available with experimental software transactional memory support.^[37] Whether this functionality will be available in the final version of the framework has not been confirmed.
On 19 October 2009, Microsoft released Beta 2 of the .NET Framework 4.^[38] At the same time, Microsoft announced the expected launch date for .NET Framework 4 as the 22 March 2010.^[38] This launch date has subsequently been delayed to April 12, 2010.^[39]
On 10 February 2010 a release candidate was published: Version:RC
On 12 April 2010 the final version of .NET Framework 4.0 was launched alongside the final release of Visual Studio 2010.
In conjunction with .NET Framework 4, Microsoft will offer a set of enhancements, codenamed Dublin, for Windows Server 2008 application server capabilities.^[40]^[41] Dublin will extend IIS to be a "standard host" for applications that use either WCF or WF.^[41]

[edit] .NET vs. Java and Java EE

The CLI and .NET languages such as C# and VB have many similarities to Sun's JVM and Java. Both are based on a virtual machine model that hides the details of the computer hardware on which their programs run. Both use their own intermediate byte-code, Microsoft calling theirs Common Intermediate Language (CIL; formerly MSIL) and Sun calling theirs Java bytecode. On .NET the byte-code is always compiled before execution, either Just In Time (JIT) or in advance of execution using the Native Image Generator utility (NGEN). With Java the byte-code is either interpreted, compiled in advance, or compiled JIT. Both provide extensive class libraries that address many common programming requirements and address many security issues that are present in other approaches. The namespaces provided in the .NET Framework closely resemble the platform packages in the Java EE API Specification in style and invocation.
.NET in its complete form (i.e., Microsoft's implementation, described in the Standardization and licensing section of this article) can only be installed on computers running a Microsoft Windows operating system^[42]^[43]^[44] whereas Java in its entirety can be installed on computers running any one of a variety of operating systems such as Linux, Solaris, Mac OS or Windows.^[45] From its beginning .NET has supported multiple programming languages and at its core remains platform agnostic and standardized so that other vendors can implement it on other platforms (although Microsoft's implementation only targets Windows, Windows CE, and Xbox platforms). The Java Virtual Machine was also designed to be both language and operating system agnostic^[46] and was launched with the slogan "Write once, run anywhere." While Java has long remained the most used language on the JVM by a wide margin, recent support for dynamic languages has increased popularity of alternatives; in particular JRuby, Scala, and Groovy.^[47] (see JVM languages).
Sun's reference implementation of Java (including the class library, the compiler, the virtual machine, and the various tools associated with the Java Platform) is open source under the GNU GPL license with Classpath exception.^[48] The source code for the .NET framework base class library is available for reference purposes only under the Microsoft Reference License.^[49]^[50]
The third-party Mono Project, sponsored by Novell, has been developing an open source implementation of the ECMA standards that are part of .NET Framework, as well as most of the other non-ECMA standardized libraries in Microsoft's .NET. The Mono implementation is meant to run on Linux, Solaris, Mac OS X, BSD, HP-UX, and Windows platforms. Mono includes the CLR, the class libraries, and compilers for C# and VB.NET. The current version supports all the APIs in version 2.0 of Microsoft's .NET. Full support exists for C# 3.0 LINQ to Objects and LINQ to XML.^[51]

[edit] Criticism

Some concerns and criticism relating to .NET include:

Applications running in a managed environment tend to require more system resources than similar applications that access machine resources more directly.
Unobfuscated managed CIL bytecode can often be easier to reverse-engineer than native code.^[52]^[53] One concern is over possible loss of trade secrets and the bypassing of license control mechanisms. Since Visual Studio .NET (2002), Microsoft has included a tool to obfuscate code (Dotfuscator Community Edition).^[54] Many other techniques^[which?] can also help to prevent reverse-engineering.
Newer versions of the framework (3.5 and up) are not pre-installed in versions of Windows below Windows 7. For this reason, applications must lead users without the framework through a procedure to install it. Some developers have expressed concerns about the large size of .NET framework runtime installers for end-users. The size is around 54 MB for .NET 3.0, 197 MB for .NET 3.5, and 250 MB for .NET 3.5 SP1 (while using web installer the typical download for Windows XP is around 50 MB, for Windows Vista - 20 MB). The size issue is partially solved with .NET 4 installer (x86 + x64) being 54 MB and not embedding full runtime installation packages for previous versions. The .NET 3.5 SP1 full installation package includes the full runtime installation packages for .NET 2.0 SP2 as well as .NET 3.0 SP2 for multiple operating systems (Windows XP/Server 2003 and Windows Vista/Server 2008) and for multiple CPU architectures (x86, x86-64, and IA-64).
- The first service pack for version 3.5 mitigates this concern by offering a lighter-weight client-only subset of the full .NET Framework. Two significant limitations should be noted, though.^[55] Firstly, the client-only subset is only an option on an existing Windows XP SP2 system that currently has no other version of the .NET framework installed. In all other scenarios, the client-only installer will install the full version of the .NET Framework 3.5 SP1. Secondly, the client-only framework does not have a 64-bit option. However, the 4 release of the .NET Framework Client Profile will be available on all operating systems and all architectures (excluding Itanium) supported by the full .NET Framework.^[56]
The .NET framework currently does not provide support for calling Streaming SIMD Extensions (SSE) via managed code. However, Mono has provided support for SIMD Extensions as of version 2.2 within the Mono.Simd namespace; Mono's lead developer Miguel de Icaza has expressed hope that this SIMD support will be adopted by the CLR ECMA standard.^[57] Streaming SIMD Extensions have been available in x86 CPUs since the introduction of the Pentium III. Some other architectures such as ARM and MIPS also have SIMD extensions. In case the CPU lacks support for those extensions, the instructions are simulated in software.
While the standards that make up .NET are inherently cross platform, Microsoft's full implementation of .NET is only supported on Windows. Microsoft does provide limited .NET subsets for other platforms such as XNA for Windows, XBOX 360 and Windows Phone 7; and Silverlight for Windows, Mac OSX, and Windows Phone 7. Alternative implementations of the CLR, base class libraries, and compilers also exist (sometimes from other vendors). While all of these implementations are based on the same standards, they are still different implementations with varying levels of completeness in comparison to the full .NET version Microsoft ships for Windows and are on occasion^{[weasel words]} incompatible.^{[citation needed]}

[edit] Alternative implementations

The Microsoft .NET Framework is the predominant implementation of .NET technologies. Other implementations for parts of the framework exist. Although the runtime engine is described by an ECMA/ISO specification, other implementations of it may be encumbered by patent issues; ISO standards may include the disclaimer, "Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights."^[58] It is more difficult to develop alternatives to the base class library (BCL), which is not described by an open standard and may be subject to copyright restrictions. Additionally, parts of the BCL have Windows-specific functionality and behavior, so implementation on non-Windows platforms can be problematic.
Some alternative implementations of parts of the framework are listed here.

Microsoft's Shared Source Common Language Infrastructure is a shared source implementation of the CLR component of the .NET Framework. However, the last version only runs on Microsoft Windows XP SP2, and does not contain all features of version 2.0 of the .NET Framework.
Microsoft's .NET Micro Framework is a .NET platform for extremely resource-constrained devices. It includes a small version of the .NET CLR and supports development in C# and debugging (in an emulator or on hardware), both using Microsoft Visual Studio. It also features a subset of the .NET base class libraries (about 70 classes with about 420 methods), a GUI framework loosely based on Windows Presentation Foundation, and additional libraries specific to embedded applications.
Mono is an implementation of the CLI and portions of the .NET Base Class Library (BCL), and provides additional functionality. It is dual-licensed under free software and proprietary software licenses. Mono is being developed by Novell, Inc. It includes support for ASP.NET, ADO.NET, and Windows Forms libraries for a wide range of architectures (including iPhone, Wii and others) and operating systems. It also includes C# and VB.NET compilers.
CrossNet is an implementation of the CLI and portions of the .NET Base Class Library (BCL). It is free software. It parses .NET assemblies and generates standard C++ code, compilable with any ANSI C++ compiler on any platform.
Portable.NET (part of DotGNU) provides an implementation of the Common Language Infrastructure (CLI), portions of the .NET Base Class Library (BCL), and a C# compiler. It supports a variety of CPUs and operating systems.

http://en.wikipedia.org/wiki/.NET_Framework_4#.NET_Framework_4
06/4/10

2010-06-04T11:06:00.002-04:00

Microsoft Windows is a series of software operating systems and graphical user interfaces produced by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces (GUIs).^[2] Microsoft Windows came to dominate the world's personal computer market, overtaking Mac OS, which had been introduced previously. As of October 2009, Windows had approximately 91% of the market share of the client operating systems for usage on the Internet.^[3]^[4]^[5] The most recent client version of Windows is Windows 7; the most recent server version is Windows Server 2008 R2; the most recent mobile device version is Windows Mobile 6.5.

[hide]

Versions

The term Windows collectively describes any or all of several generations of Microsoft operating system products. These products are generally categorized as follows:

Early versions

Main articles: Windows 1.0, Windows 2.0, and Windows 2.1x

Windows 1.0, the first version, released in 1985

The history of Windows dates back to September 1981, when the project named "Interface Manager" was started. It was announced in November 1983 (after the Apple Lisa, but before the Macintosh) under the name "Windows", but Windows 1.0 was not released until November 1985.^[6] The shell of Windows 1.0 was a program known as the MS-DOS Executive. Other supplied programs were Calculator, Calendar, Cardfile, Clipboard viewer, Clock, Control Panel, Notepad, Paint, Reversi, Terminal, and Write. Windows 1.0 did not allow overlapping windows, due to Apple Computer owning this feature^{[citation needed]}. Instead all windows were tiled. Only dialog boxes could appear over other windows.
Windows 2.0 was released in October 1987 and featured several improvements to the user interface and memory management.^[6] Windows 2.0 allowed application windows to overlap each other and also introduced more sophisticated keyboard-shortcuts. It could also make use of expanded memory.
Windows 2.1 was released in two different flavors: Windows/386 employed the 386 virtual 8086 mode to multitask several DOS programs, and the paged memory model to emulate expanded memory using available extended memory. Windows/286 (which, despite its name, would run on the 8086) still ran in real mode, but could make use of the high memory area.
The early versions of Windows were often thought of as simply graphical user interfaces, mostly because they ran on top of MS-DOS and used it for file system services.^[7] However, even the earliest 16-bit Windows versions already assumed many typical operating system functions; notably, having their own executable file format and providing their own device drivers (timer, graphics, printer, mouse, keyboard and sound) for applications. Unlike MS-DOS, Windows allowed users to execute multiple graphical applications at the same time, through cooperative multitasking. Windows implemented an elaborate, segment-based, software virtual memory scheme, which allowed it to run applications larger than available memory: code segments and resources were swapped in and thrown away when memory became scarce, and data segments moved in memory when a given application had relinquished processor control, typically waiting for user input.^{[citation needed]}

Windows OS market share
Source	Net Market Share^[8]	W3Counter^[9]	StatCounter^[10]
Date	April 2010	April 2010	May 2010
All versions	91.33%	84.55%	92.32%
Windows XP	63.41%	51.86%	58.02%
Windows Vista	15.6%	18.19%	19.46%
Windows 7	11.68%	13.21%	14.84%
Windows 2000	0.5%	0.39%	—
Windows 98	0.07%	—	—
Windows CE	0.04%	—	—
Windows Me	0.03%	—	—
Windows Server 2003	—	0.9%	—

Windows 3.0 and 3.1

Main articles: Windows 3.0 and Windows 3.1x

Windows 3.0, released in 1990

Windows 3.0 (1990) and Windows 3.1 (1992) improved the design, mostly because of virtual memory and loadable virtual device drivers (VxDs) which allowed them to share arbitrary devices between multitasked DOS windows.^{[citation needed]} Also, Windows applications could now run in protected mode (when Windows was running in Standard or 386 Enhanced Mode), which gave them access to several megabytes of memory and removed the obligation to participate in the software virtual memory scheme. They still ran inside the same address space, where the segmented memory provided a degree of protection, and multi-tasked cooperatively. For Windows 3.0, Microsoft also rewrote critical operations from C into assembly, making this release faster and less memory-hungry than its predecessors.^{[citation needed]} With the introduction of Windows for Workgroups 3.11, Windows was able to bypass DOS for file management operations using 32-bit file access.^{[citation needed]}

Windows 95, 98, and Me

Main articles: Windows 95, Windows 98, and Windows Me

Windows 95, released in 1995

Windows 95 was released in August 1995, featuring a new user interface, support for long file names of up to 255 characters, and the ability to automatically detect and configure installed hardware (plug and play). It could natively run 32-bit applications, and featured several technological improvements that increased its stability over Windows 3.1. There were several OEM Service Releases (OSR) of Windows 95, each of which was roughly equivalent to a service pack.
Microsoft's next release was Windows 98 in June 1998. Microsoft released a second version of Windows 98 in May 1999, named Windows 98 Second Edition (often shortened to Windows 98 SE).
In September 2000, Microsoft released Windows Me (Me standing for Millennium Edition), which updated the core from Windows 98 but adopted some aspects of Windows 2000 and removed the "boot in DOS mode" option. It also added a new feature called System Restore, allowing the user to set the computer's settings back to an earlier date.

Windows NT family

Main article: Windows NT

The NT family of Windows systems was fashioned and marketed for higher reliability business use. The first release was NT 3.1 (1993), numbered "3.1" to match the consumer Windows version, which was followed by NT 3.5 (1994), NT 3.51 (1995), NT 4.0 (1996), and Windows 2000 (2000). 2000 is the last NT-based Windows release which does not include Microsoft Product Activation. NT 4.0 was the first in this line to implement the "Windows 95" user interface (and the first to include Windows 95’s built-in 32-bit runtimes).
Microsoft then moved to combine their consumer and business operating systems with Windows XP, coming in both home and professional versions (and later niche market versions for tablet PCs and media centers); they also diverged release schedules for server operating systems. Windows Server 2003, released a year and a half after Windows XP, brought Windows Server up to date with MS Windows XP. After a lengthy development process, Windows Vista was released toward the end of 2006, and its server counterpart, Windows Server 2008 was released in early 2008. On July 22, 2009, Windows 7 and Windows Server 2008 R2 were released as RTM (release to manufacturing). Windows 7 was released on October 22, 2009.

64-bit operating systems

Windows NT included support for several different platforms before the x86-based personal computer became dominant in the professional world. Versions of NT from 3.1 to 4.0 variously supported PowerPC, DEC Alpha and MIPS R4000, some of which were 64-bit processors, although the operating system treated them as 32-bit processors.
With the introduction of the Intel Itanium architecture (also known as IA-64), Microsoft released new versions of Windows to support it. Itanium versions of Windows XP and Windows Server 2003 were released at the same time as their mainstream x86 (32-bit) counterparts. On April 25, 2005, Microsoft released Windows XP Professional x64 Edition and Windows Server 2003 x64 Editions to support the x86-64 (or x64 in Microsoft terminology) architecture. Microsoft dropped support for the Itanium version of Windows XP in 2005. Windows Vista is the first end-user version of Windows that Microsoft has released simultaneously in x86 and x64 editions. Windows Vista does not support the Itanium architecture. The modern 64-bit Windows family comprises AMD64/Intel64 versions of Windows Vista, and Windows Server 2008, in both Itanium and x64 editions. Windows Server 2008 R2 drops the 32-bit version, although Windows 7 does not.

Windows CE

Windows CE 5.0

Main article: Windows CE

Windows CE (officially known as Windows Embedded Compact), is an edition of Windows that runs on minimalistic computers, like satellite navigation systems and some mobile phones. Windows Embedded Compact is based on its own dedicated kernel, dubbed Windows CE kernel. Windows CE was used in the Dreamcast along with Sega's own proprietary OS for the console. Windows CE is the core from which Windows Mobile is derived.
Windows Embedded Compact is not to be confused with Windows XP Embedded or Windows NT 4.0 Embedded, modular editions of Windows based on Windows NT kernel.

History

Main article: History of Microsoft Windows

The Windows family tree.

Microsoft has taken two parallel routes in its operating systems. One route has been for the home user and the other has been for the professional IT user. The dual routes have generally led to home versions having greater multimedia support and less functionality in networking and security, and professional versions having inferior multimedia support and better networking and security.^{[citation needed]}
The first version of Microsoft Windows, version 1.0, released in November 1985, lacked a degree of functionality and achieved little popularity, and was to compete with Apple’s own operating system.^{[citation needed]} Windows 1.0 is not a complete operating system; rather, it extends MS-DOS. Microsoft Windows version 2.0 was released in November, 1987 and was slightly more popular than its predecessor. Windows 2.03 (release date January 1988) had changed the OS from tiled windows to overlapping windows. The result of this change led to Apple Computer filing a suit against Microsoft alleging infringement on Apple's copyrights.^[11]^[12]
Microsoft Windows 3.0, released in 1990, was the first Microsoft Windows version to achieve broad commercial success, selling 2 million copies in the first six months.^[13]^[14] It featured improvements to the user interface and to multitasking capabilities. It received a facelift in Windows 3.1, made generally available on March 1, 1992. Windows 3.1 support ended on December 31, 2001.^[15]
In July 1993, Microsoft released Windows NT based on a new kernel. NT was considered to be the professional OS and was the first Windows version to utilize preemptive multitasking.^{[citation needed]}. Windows NT would later be retooled to also function as a home operating system, with Windows XP.
On August 24, 1995, Microsoft released Windows 95, a new, and major, consumer version that made further changes to the user interface, and also used preemptive multitasking. Windows 95 was designed to replace not only Windows 3.1, but also Windows for Workgroups, and MS-DOS. It was also the first Windows operating system to use Plug and Play capabilities. The changes Windows 95 brought to the desktop were revolutionary, as opposed to evolutionary, such as those in Windows 98 and Windows Me. Mainstream support for Windows 95 ended on December 31, 2000 and extended support for Windows 95 ended on December 31, 2001.^[16]
The next in the consumer line was Microsoft Windows 98 released on June 25, 1998. It was substantially criticized for its slowness and for its unreliability compared with Windows 95, but many of its basic problems were later rectified with the release of Windows 98 Second Edition (98SE) in 1999. Mainstream support for Windows 98 ended on June 30, 2002 and extended support for Windows 98 ended on July 11, 2006.^[17]
As part of its "professional" line, Microsoft released Windows 2000 in February 2000. During 2004 part of the Source Code for Windows 2000 was leaked onto the internet. This was bad for Microsoft as the same kernel used in Windows 2000 was used in Windows XP. The consumer version following Windows 98 was Windows Me (Windows Millennium Edition). Released in September 2000, Windows Me implemented a number of new technologies for Microsoft: most notably publicized was "Universal Plug and Play". Windows Me was criticized a lot, due to slownesses, freezes and hardware problems.
In October 2001, Microsoft released Windows XP, a version built on the Windows NT kernel that also retained the consumer-oriented usability of Windows 95 and its successors. This new version was widely praised in computer magazines.^[18] It shipped in two distinct editions, "Home" and "Professional", the former lacking many of the superior security and networking features of the Professional edition. Additionally, the first "Media Center" edition was released in 2002,^[19] with an emphasis on support for DVD and TV functionality including program recording and a remote control. Mainstream support for Windows XP ended on April 14, 2009. Extended support will continue until April 8, 2014.^[20]
In April 2003, Windows Server 2003 was introduced, replacing the Windows 2000 line of server products with a number of new features and a strong focus on security; this was followed in December 2005 by Windows Server 2003 R2.
On January 30, 2007 Microsoft released Windows Vista. It contains a number of new features, from a redesigned shell and user interface to significant technical changes, with a particular focus on security features. It is available in a number of different editions, and has been subject to some criticism.

Timeline of releases

Main article: Timeline of Microsoft Windows

Release date	Product name	Current Version / Build	Notes	Last IE
November 1985	Windows 1.01	1.01	Unsupported	-
November 1987	Windows 2.03	2.03	Unsupported	-
May 1988	Windows 2.10	2.10	Unsupported	-
March 1989	Windows 2.11	2.11	Unsupported	-
May 1990	Windows 3.0	3.0	Unsupported	-
March 1992	Windows 3.1x	3.1	Unsupported	5
October 1992	Windows For Workgroups 3.1	3.1	Unsupported	5
July 1993	Windows NT 3.1	NT 3.1	Unsupported	5
December 1993	Windows For Workgroups 3.11	3.11	Unsupported	5
January 1994	Windows 3.2 (released in Simplified Chinese only)	3.2	Unsupported	5
September 1994	Windows NT 3.5	NT 3.5	Unsupported	5
May 1995	Windows NT 3.51	NT 3.51	Unsupported	5
August 1995	Windows 95	4.0.950	Unsupported	5.5
July 1996	Windows NT 4.0	NT 4.0.1381	Unsupported	6
June 1998	Windows 98	4.10.1998	Unsupported	6
May 1999	Windows 98 SE	4.10.2222	Unsupported	6
February 2000	Windows 2000	NT 5.0.2195	Extended Support until July 13, 2010^[21]	6
September 2000	Windows Me	4.90.3000	Unsupported	6
October 2001	Windows XP	NT 5.1.2600	Extended Support until July 13, 2010 for SP2 and April 8, 2014 for SP3. (RTM and SP1 unsupported).	8
March 2003	Windows XP 64-bit Edition (IA-64)	NT 5.2.3790	Unsupported	6
April 2003	Windows Server 2003	NT 5.2.3790	Current (RTM unsupported).	8
April 2005	Windows XP Professional x64 Edition	NT 5.2.3790	Extended Support until July 13, 2010 for SP2 and April 8, 2014 for SP3. (RTM and SP1 unsupported).	8
July 2006	Windows Fundamentals for Legacy PCs	NT 5.1.2600	Current	8
November 2006 (volume licensing) January 2007 (retail)	Windows Vista	NT 6.0.6002	Current (RTM unsupported). Version changed to NT 6.0.6001 with SP1 (February 4, 2008) and to NT 6.0.6002 with SP2 (April 28, 2009).	9
July 2007	Windows Home Server	NT 5.2.4500	Current	8
February 2008	Windows Server 2008	NT 6.0.6002	Current Version changed to NT 6.0.6002 with SP2 (April 28, 2009).	9
October 2009 ^[22]	Windows 7 and Windows Server 2008 R2	NT 6.1.7600	Current	9
2012	Windows 8	Unknown	Upcoming	Unknown

Security

This article may need to be updated. Please update this article to reflect recent events or newly available information, and remove this template when finished. Please see the talk page for more information.

Consumer versions of Windows were originally designed for ease-of-use on a single-user PC without a network connection, and did not have security features built in from the outset.^[23] However, Windows NT and its successors are designed for security (including on a network) and multi-user PCs, but were not initially designed with Internet security in mind as much, since, when it was first developed in the early 1990s, Internet use was less prevalent.^[24]
These design issues combined with programming errors (e.g. buffer overflows) and the popularity of Windows means that it is a frequent target of computer worm and virus writers. In June 2005, Bruce Schneier’s Counterpane Internet Security reported that it had seen over 1,000 new viruses and worms in the previous six months.^[25]
Microsoft releases security patches through its Windows Update service approximately once a month (usually the second Tuesday of the month), although critical updates are made available at shorter intervals when necessary.^[26] In versions of Windows after and including Windows 2000 SP3 and Windows XP, updates can be automatically downloaded and installed if the user selects to do so. As a result, Service Pack 2 for Windows XP, as well as Service Pack 1 for Windows Server 2003, were installed by users more quickly than it otherwise might have been.^[27]
While the Windows 9x series offered the option of having profiles for multiple users, they had no concept of access privileges, and did not allow concurrent access; and so were not true multi-user operating systems. In addition, they implemented only partial memory protection. They were accordingly widely criticised for lack of security.
The Windows NT series of operating systems, by contrast, are true multi-user, and implement absolute memory protection. However, a lot of the advantages of being a true multi-user operating system were nullified by the fact that, prior to Windows Vista, the first user account created during the setup process was an administrator account, which was also the default for new accounts. Though Windows XP did have limited accounts, the majority of home users did not change to an account type with fewer rights – partially due to the number of programs which unnecessarily required administrator rights – and so most home users ran as administrator all the time.
Windows Vista changes this^[28] by introducing a privilege elevation system called User Account Control. When logging in as a standard user, a logon session is created and a token containing only the most basic privileges is assigned. In this way, the new logon session is incapable of making changes that would affect the entire system. When logging in as a user in the Administrators group, two separate tokens are assigned. The first token contains all privileges typically awarded to an administrator, and the second is a restricted token similar to what a standard user would receive. User applications, including the Windows Shell, are then started with the restricted token, resulting in a reduced privilege environment even under an Administrator account. When an application requests higher privileges or "Run as administrator" is clicked, UAC will prompt for confirmation and, if consent is given (including administrator credentials if the account requesting the elevation is not a member of the administrators group), start the process using the unrestricted token.^[29]

File permissions

All Windows versions from Windows NT 3 have been based on a file system permission system referred to as AGLP (Accounts, Global, Local, Permissions) AGDLP which in essence where file permissions are applied to the file/folder in the form of a 'local group' which then has other 'global groups' as members. These global groups then hold other groups or users depending on different Windows versions used. This system varies from other vendor products such as Linux and NetWare due to the 'static' allocation of permission being applied directory to the file or folder. However using this process of AGLP/AGDLP/AGUDLP allows a small number of static permissions to be applied and allows for easy changes to the account groups without reapplying the file permissions on the files and folders.

Windows Defender

On January 6, 2005, Microsoft released a Beta version of Microsoft AntiSpyware, based upon the previously released Giant AntiSpyware. On February 14, 2006, Microsoft AntiSpyware became Windows Defender with the release of Beta 2. Windows Defender is a freeware program designed to protect against spyware and other unwanted software. Windows XP and Windows Server 2003 users who have genuine copies of Microsoft Windows can freely download the program from Microsoft's web site, and Windows Defender ships as part of Windows Vista and 7.^[30]

Third-party analysis

In an article based on a report by Symantec,^[31] internetnews.com has described Microsoft Windows as having the "fewest number of patches and the shortest average patch development time of the five operating systems it monitored in the last six months of 2006."^[32]
A study conducted by Kevin Mitnick and marketing communications firm Avantgarde in 2004 found that an unprotected and unpatched Windows XP system with Service Pack 1 lasted only 4 minutes on the Internet before it was compromised, and an unprotected and also unpatched Windows Server 2003 system was compromised after being connected to the internet for 8 hours.^[33] However, it is important to note that this study does not apply to Windows XP systems running the Service Pack 2 update (released in late 2004), which vastly improved the security of Windows XP.^{[citation needed]} The computer that was running Windows XP Service Pack 2 was not compromised. The AOL National Cyber Security Alliance Online Safety Study of October 2004 determined that 80% of Windows users were infected by at least one spyware/adware product.^[34] Much documentation is available describing how to increase the security of Microsoft Windows products. Typical suggestions include deploying Microsoft Windows behind a hardware or software firewall, running anti-virus and anti-spyware software, and installing patches as they become available through Windows Update.^[35]

Emulation software

Emulation allows the use of some Windows applications without using Microsoft Windows. These include:
Wine — a free and open source software implementation of the Windows API, allowing one to run many Windows applications on x86-based platforms, including Linux and Mac OS X. Wine developers refer to it as a "compatibility layer";^[36] and make use of Windows-style APIs to emulate the Windows environment.

CrossOver — A Wine package with licensed fonts. Its developers are regular contributors to Wine, and focus on Wine running officially supported applications.
Cedega — TransGaming Technologies' proprietary fork of Wine, designed specifically for running games written for Microsoft Windows under Linux. A version of Cedega known as Cider is used by some video game publishers to allow Windows games to run on Mac OS X. Since wine was licensed under the LGPL Cedega has been unable to port the improvements made to wine to their proprietary codebase.

http://en.wikipedia.org/wiki/Microsoft_Windows
06/04/10

MAC OS X Snow Leopard

2010-06-04T11:04:00.000-04:00

Mac OS X Snow Leopard (version 10.6) is the seventh and current major release of Mac OS X, Apple's desktop and server certified Unix operating system.^[2]
Snow Leopard was announced by Steve Jobs on June 8, 2008 at WWDC 2008 but was not publicly unveiled until the following year on June 8, 2009 at the same conference. On August 28, 2009, it was released worldwide,^[3] and was made available for purchase from Apple's website and its retail stores at the price of $29 for a single-user license. As a result of the low price, initial sales of Snow Leopard were significantly higher than that of its predecessors.^[4] The release of Snow Leopard came nearly two years after the introduction of Mac OS X v10.5 "Leopard," the second longest time span between successive Mac OS X releases.
Unlike previous versions of Mac OS X, the goal with Snow Leopard was to improve performance, efficiency and reduce its overall memory footprint instead of to add new end-user features. Much of the software in Mac OS X was extensively rewritten for this release in order to fully take advantage of modern Macintosh hardware. New programming languages, such as OpenCL, were created, allowing software developers to use graphics cards in their applications. This is also the first Mac OS release since the introduction of System 7.1.2 that does not support the PowerPC architecture, as Apple now intends to focus on its current line of Intel-based products.^[5]

[edit] System requirements

Apple states the following basic Snow Leopard system requirements are:

Mac computer with an Intel processor (IA-32). "Yonah" processors such as Core Solo and Core Duo can run only 32-bit applications; later x86-64 architecture processors such as Core 2 will also be able to run 64-bit applications.
1 GB of RAM
5 GB of free disk space
DVD drive (also accessible via Remote Disc) or external USB or FireWire DVD drive for installation

Additional requirements to use certain features:^[6]

QuickTime H.264 hardware acceleration support, requires an Nvidia GeForce 9400M, 320M, or GT 330M graphics card
OpenCL, requires a supported Nvidia or ATI graphics card^[6]

Snow Leopard does not support PowerPC-based Macs (e.g., Power Macs, PowerBooks, iBooks, iMacs (G3-G5), all eMacs, plus pre-February 2006 Mac minis and the Power Mac G4 Cube), although PowerPC applications are supported via Rosetta, which is now an optional install.

[edit] Usage on unsupported hardware

Main article: OSx86

Some ways of running 10.6 Snow Leopard on certain unsupported hardware have been discovered. Users who have access to supported hardware have installed Snow Leopard on the supported machine then simply moved the hard drive to the unsupported machine. Alternatively, the Snow Leopard Installation DVD can be booted on a supported Mac, then installed on an unsupported Mac via the Firewire Target Disk Mode.
Since Apple moved to using Intel processors in their computers, the OSx86 project has developed and now also allows Mac OS X Tiger and Leopard to be installed and run successfully on non-Apple x86-based computers, albeit in violation of Apple's licensing agreement for OS X. A variety of installation processes can be used, the most common being to use modified Darwin bootloaders commonly known as "Boot 132" designed to trick the retail, or vanilla, operating system into thinking that it is running on an EFI-based Mac. This method of installation allows the use of an unmodified Apple installation DVD and the updating of the operating system from the built-in Software Update utility, but will work only on Intel Core-based PCs, unless a modified kernel is added to the pre-boot cd. Modified installation DVDs are also available illegally which offer a more outdated approach to installing. A hardware device capable of being attached to a PC’s motherboard has also been released, EFI-X, enabling much the same function as the modified Darwin bootloader.

[edit] License

Snow Leopard is available as an upgrade for Intel-based Macintosh computers. Single-user licenses and "family pack" licenses for up to five computers are available. For qualifying Mac computers bought after June 8, 2009 Apple offered a discounted price through their "up to date" program provided your order was faxed or postmarked by December 26, 2009. While the license for the standalone retail version of Snow Leopard restricts that upgrade to users of Mac OS X v10.5 "Leopard", the company has acknowledged that there is no technical barrier preventing a direct upgrade from Mac OS X v10.4 "Tiger."^[7] The recommended upgrade path from Apple for OS X "Tiger" is through the current release of the "Mac Box Set," which includes Mac OS X Snow Leopard, iLife '09, and iWork '09.
There are three licenses available.^[8] These licenses differ in their requirements for pre-installed versions of Mac OS X:

Leopard Upgrade: requires that Mac OS X 10.5 Leopard already be installed.

Subject to the terms and conditions of this License, you are granted a limited non-exclusive license to install, use and run one (1) copy of the Apple Software on a single Apple-branded computer as long as that computer has a properly licensed copy of Mac OS X Leopard already installed on it.^[9]

Single Use: places no restriction on which (if any) version of Mac OS X should already be installed. Used for the non-upgrade and Mac Box Set versions of Snow Leopard.

Subject to the terms and conditions of this License ... you are granted a limited non-exclusive license to install, use and run one (1) copy of the Apple Software on a single Apple-branded computer at a time.^[9]

Family Pack: identical to the Single Use license, in this respect.

The license Apple's website^[10] advertises as "upgrade from Mac OS X Leopard for $29" is not the Leopard Upgrade license, but the Single Use license.

The Snow Leopard single user license will be available for a suggested retail price of $29 (US)^[11]

The Snow Leopard Upgrade license applies only to the Up-To-Date Program^[12] (US$9.95) for Macs bought between June 8 and December 26, 2009.^[13] and the installation discs provided through this program are clearly marked as upgrades unlike either of the retail editions.

[edit] New or changed features

Mac OS X v10.6 is intended to be a release aimed to refine the existing feature set, expand the technological capabilities of the operating system, and improve application efficiency. Many of the changes involve how the system works in the background and are not intended to be seen by the user. For example, the Finder application was completely rewritten in the 64-bit Cocoa programming language. Despite significant changes in the software, users will experience almost no changes in the user interface. Snow Leopard includes the following changes:

Boot Camp now allows Windows partitions to read and copy files from HFS+ partitions. The new version also adds support for advanced features on Cinema Displays and a new command-line version of the Startup Disk Control Panel.
The Finder has been completely rewritten in 64-bit Cocoa to take advantage of the new technologies introduced in Snow Leopard.
A much smaller OS footprint, taking up about 7 GB less space than Mac OS X v10.5. Some of the recovered disk space (~250 MB) is due to the fact that printer drivers are now downloaded or installed only as needed, rather than being pre-installed. The default install only contains those drivers needed for existing printers and a small subset of popular printers.^[14]
iChat enhancements include greater resolution video chats in iChat Theater and lowered upload bandwidth requirements.
Microsoft Exchange support is now integrated into the Mail, Address Book, and iCal applications. However, only Microsoft Exchange 2007 is supported and customers using prior versions of Exchange must either upgrade or use Microsoft Entourage.
Full multi-touch trackpad support has been added to notebooks prior to those introduced in October 2008.^[15] While the original MacBook Air and other early multi-touch trackpad enabled notebooks had support for some gestures, they were unable to use four-finger gestures. This limitation has now been removed in Snow Leopard.
Preview now has artificial intelligence algorithms that allow it to infer the structure of a paragraph in a PDF document.
QuickTime X, the next version of QuickTime player and multimedia framework, has been completely rewritten into a full 64-bit Cocoa application and builds on the media technologies in Mac OS X, such as Core Audio, Core Video, and Core Animation, to deliver playback. Apple has redesigned the QuickTime user interface to resemble the full-screen QuickTime view in prior versions, where the entire window displays the video. The titlebar and playback controls fade in and out as needed. QuickTime X also supports HTTP live streaming and takes advantage of ColorSync to provide high-quality color reproduction.^[16] If Snow Leopard is installed on a Mac with an nVidia GeForce 9400M, 320M or GT 330M graphics card, QuickTime X will be able to use its video-decoding capabilities to reduce CPU load.
Safari 4 features Top Sites, Cover Flow, VoiceOver, expanded standards support, and built-in crash resistance, which prevents browser crashes caused by plug-ins by running them in separate processes. Safari 4 is bundled with Snow Leopard but does not require it, as it is available for free for Mac OS X 10.4 (Tiger), 10.5 (Leopard) as well as Windows.
Time Machine connection establishment and backups are now much faster.
VoiceOver has also been greatly enhanced in Snow Leopard. Reading of web pages is improved with Auto Web Spots — areas of a page automatically designated for quick access. On newer Apple portables, trackpad gestures can be used to control VoiceOver functions, including the "rotor" gesture first seen in VoiceOver for the iPhone 3GS, allowing for the changing of certain VoiceOver navigation options by rotating fingers on the trackpad. Braille Display support is also improved, with Bluetooth displays supported for the first time.^[17]

[edit] Refinements to the user interface

While the Finder was completely rewritten in 64-bit Cocoa, it did not receive a major user interface overhaul. Instead, the interface has been modified in several areas to promote ease of use. These changes include:

Exposé can now display windows for a single program by left clicking and holding its icon in the dock. Windows are arranged in a new grid pattern.
Contextual menus which come out of Dock icons now have more options and have a new look, with a semi-transparent charcoal background and white text.
Dock Stacks, when viewed as a grid, allow viewing of a subfolder as a new stack, rather than launching a Finder window, in a manner similar to “tunnelling”. When viewed as grids or lists, scroll-bars are provided to navigate folders with more items than the current screen resolution will accommodate.^[18]
The default gamma has been changed from 1.8 to 2.2 to better serve the color needs of digital content producers and consumers.^[14]
Windows can now be minimized directly onto their application's icon in the dock.^[19]
Faster PDF and JPEG icon refreshes.^[20]
When searching for a network, the AirPort menu-bar icon animates until it finds a network and shows network strength of available networks in the drop down menu.
Prefixes for bytes are now used in strictly decimal meaning (as opposed to their binary meaning) when describing disk space, such that an indicated file size of 1 MB corresponds to 1 million bytes, as commonly used by hard disk manufacturers.^[21]
Snow Leopard shuts down and goes to sleep faster.^[22]

[edit] New wallpapers

As with most upgrades of Mac OS, new wallpapers are available. There are new wallpapers in the Nature (two of which are of snow leopards), Plants and Black and White sub-folders under the Apple folder. Furthermore, there are new Apple wallpaper sub-folders with multiple wallpapers:

Art: Dancer on the Stage, Nighthawks, Poppies Blooming, Sunday Afternoon, Suprematism, The Great Wave, and Water Lilies.
Patterns: Pinstripe and Saree.

New solid colors can be used as wallpapers as well. There is a new blue and gray, as well as a solid kelp which serves as the "green wallpaper." The default "space nebula" wallpaper has been updated as well.

[edit] Dropped features

It is no longer possible to change an application's language using the Finder "Get Info" dialogue. While there are workarounds for some applications, others (such as Adobe After Effects CS4) will not be able to be run in a different language than the one installed^[23] without using Terminal codes or 3rd party software.
Creator code, a hidden code that defines what application should open a specific file regardless of its extension, is no longer supported^[24].

[edit] Developer technologies

[edit] 64-bit architecture

Mac OS X Tiger added limited support for 64-bit applications on machines with 64-bit processors; Leopard extended the support for 64-bit applications to include applications using most of Mac OS X's libraries and frameworks.
In Snow Leopard, most built-in applications have been rebuilt to leverage the 64-bit x86-64 architecture (excluding iTunes, Front Row, Grapher and DVD Player applications).^[25] They will run in 32-bit mode on machines with 32-bit processors, and in 64-bit mode on machines with 64-bit processors.
In addition, the Mac OS X kernel has been rebuilt to run in 64-bit mode on some machines. On those machines, Snow Leopard supports up to 16 terabytes of RAM. Newer Xserve and Mac Pro machines will run a 64-bit kernel by default; newer iMac machines can run a 64-bit kernel, but will not do so by default.^[26] Users wishing to use the 64-bit kernel on those machines must hold down the numbers 6 and 4 on the keyboard while booting to get the 64-bit kernel to load.^[27]^[28] A change to the com.apple.Boot.plist will also enable users with compatible computers to permanently boot into 64-bit for those wishing to do so.
Stuart Harris, software product marketing manager at Apple Australia, said, "For the most part, everything that they experience on the Mac, from the 64-bit point of view, the applications, the operating system, is all going to be 64-bit, but that at this stage there were very few things, such as device drivers, that required 64-bit mode at the kernel level".^[28]
As of version 10.6.0, only the following Apple computers are capable of running the 64-bit kernel:^[29]^[30]

Product	Model name	K64 status
Early 2008 Mac Pro	MacPro3,1	Capable
Early 2008 Xserve	Xserve2,1	Default
MacBook Pro 15″/17″	MacBookPro4,1	Capable
iMac	iMac8,1	Capable
Unibody MacBook 13″	MacBook5,1	Capable
Unibody MacBook Pro 13″	MacBookPro5,5	Capable
Unibody MacBook Pro 15″	MacBookPro5,1	Capable
Unibody MacBook Pro 17″	MacBookPro5,2	Capable
Mac Pro	MacPro4,1	Capable
iMac	iMac9,1	Capable
Early 2009 Xserve	Xserve3,1	Default
Early 2009 Mac mini	Macmini3,1	Capable

^* Amit Singh has reported that the early 2009 Mac Mini and MacBook may be capable of running the 64-bit kernel; however, Apple has set these models to boot into the 32-bit kernel. With some tweaking, the Unibody MacBook can be set to boot the 64-bit kernel and possibly other models as well.^[31]

[edit] Grand Central Dispatch

Grand Central Dispatch uses the multiple processor cores now in every new Macintosh for more efficient performance. Due to the technical difficulties traditionally involved in making applications optimized for multicore CPUs, the majority of computer applications do not effectively use multiple processor cores.^[32] As a result, processing power often goes unused. Grand Central Dispatch includes APIs to help programmers efficiently use these cores for parallel programming.
Grand Central Dispatch shifts thread handling focus to itself rather than leaving it to specific applications to distribute jobs evenly across cores and clears up unused memory created by inactive or old threads to achieve maximum performance. Apple is also releasing APIs for Grand Central Dispatch for developers to use in their applications and also to analyze specific blocks of code running on Grand Central Dispatch.^[33]
A new C and Objective-C language feature named "Blocks" facilitates creation of code that will easily optimize to take advantage of Grand Central Dispatch.^[34]^[35]^[36]

[edit] OpenCL

OpenCL (Open Computing Language) addresses the power of graphics processing units (GPUs) to leverage them in any application, and not just for graphics-intensive applications like 3D games. OpenCL automatically optimizes for the kind of graphics processor in the Mac, adjusting itself to the available processing power. OpenCL provides consistent numeric precision and accuracy, fixing a problem that has hampered GPU-based programming in the past.^[37]
OpenCL is a C-based programming language with a structure that is already familiar to Mac OS X programmers, who can use Xcode developer tools to adapt their programs to work with OpenCL. Only the most process intensive parts of the application need to be written in OpenCL C without affecting the rest of the code. OpenCL is an open standard that has been supported by AMD, Intel, and Nvidia; it is maintained by Khronos Group.^[16]
It serves a similar purpose to Nvidia's C for CUDA and Microsoft's future Direct3D 11 computer shaders.
It only works with the following Mac GPUs: NVIDIA GeForce 320M, GT 330M, 9400M, 9600M GT, 8600M GT, GT 120, GT 130, GTX 285, 8800 GT, 8800 GS, Quadro FX 4800, FX 5600 and ATI Radeon HD 4670, HD 4850, HD 4870.^[6]

[edit] CUPS

CUPS (the printing system used in many Unix-like operating systems) has been updated to version 1.4 which provides improved driver, networking, and Kerberos support along with performance improvements. CUPS 1.4 is also the first implementation of the Internet Printing Protocol version 2.1.^[38]

[edit] Power management

Power management has been improved, with implementation of a new wake on demand feature supported on more recent Macintosh hardware.^[39] Wake on demand takes advantage of the sleep proxy service implemented in AirPort and Time Capsule routers,^[40] so that the computer can sleep while the router responds to mDNS queries. Should the request require the host computer to wake up, the router sends the necessary special wake-up-packet^[41] to the sleeping computer.

[edit] Security

An anti-malware feature was added to the system that alerts the user if malware is detected.^[42]
Computer security researcher Charlie Miller claims that OS X Snow Leopard is more vulnerable to attack than Microsoft Windows for lacking full address space layout randomization (ASLR) since OS X v10.5,^[43] which Microsoft has implemented since Windows Vista.^[44]
Despite the lack of ASLR, Apple has strengthened OS X by implementing stack protection, and sandboxing more OS X components such as the H.264 decoder in QuickTime and browser plug-ins as a separate process in Safari.^[45]

[edit] Compatibility

Snow Leopard breaks compatibility with versions of some applications, including Parallels Desktop 3.0, versions of Aperture before 2.1.1, and versions of Keynote before 2.0.2, among other software.^[46] Apple has also published an official list of applications with compatibility issues with Snow Leopard.
Printer and scanner drivers used by previous versions of Mac OS X are not compatible with Snow Leopard and will be replaced during Snow Leopard installation. Since the initial release of Snow Leopard many manufacturers have provided compatible drivers that are available via Software Update.^[47] If a native driver is not available Snow Leopard also includes CUPS and Gutenprint open source drivers that may provide limited functionality.

[edit] Reception

Mac OS X Snow Leopard was well-received by critics.^[48]^[49] Apple had stated in the advertising of Snow Leopard from its first demo at the WWDC 2009 that Snow Leopard features no new major visual changes.^[50] Instead, the release focuses on refining the operating system to enable better performance.^[50]
The price of Snow Leopard has dropped from the $129 Apple charged for previous versions of Mac OS X to $29. This could be largely due to the fact that most users would not see a noticeable change in the look and feel of the system.^[51] However, most reviews commented on the large improvement in speed of the native Mac OS X applications Finder, iCal, Mail, etc.^[51]
Other unexpected improvements were the release of a new version of Boot Camp, version 3.0, a cleaner, popup software update process and screen and video recording in the new QuickTime Player.^[52]
CNET editors gave it 4 stars out of 5, stating "Intel Mac users will like Snow Leopard's smartly designed interface enhancements, and its Exchange support is a must-have (especially with Outlook for Mac on the way). With a ton of technological improvements, Snow Leopard is worth the $29 upgrade fee."^[53]
The single-user upgrade and Family Pack units of Snow Leopard ranked 1 and 2 respectively on Amazon.com's software bestseller charts when Apple announced it would release it within the week.^[54]
More critically, SFGate blogger Yobie Benjamin wrote that the "Macbook Pro that came preloaded with Snow Leopard kicks butt and is a screaming fast machine", but "when I tried to upgrade one of my 'older' Macbooks, it was a fricking disaster from hell". Benjamin complained of slowness even after an upgrade install and a later clean install on the older machine, which he ended up downgrading back to Leopard.^[55]
A bug in Mac OS X versions 10.6 and 10.6.1 which, in rare cases, caused loss of user account data after use of a previously-existing guest account by users who had upgraded from a previous version of Mac OS X, received wide publicity.^[56] The bug was fixed as of version 10.6.2.^[57]

[edit] Release history

Apple CEO Steve Jobs announced Snow Leopard at WWDC on June 9, 2008, and it was privately demonstrated to developers by Senior Vice President of Software Engineering Bertrand Serlet. The first public demonstration was given at WWDC 2009 by Serlet and Vice President of Mac OS Engineering, Craig Federighi.^[5]^[58]

Version	Build^[59]	Date	OS name	Notes	Download
10.6	10A432	August 28, 2009	Darwin 10.0	Original retail DVD release	N/A
10.6	10A433	August 28, 2009	Darwin 10.0	Server edition; Original retail DVD release	N/A
10.6.1	10B504	September 10, 2009	Darwin 10.1	About the Mac OS X v10.6.1 Update	Mac OS X v10.6.1 Update
10.6.2	10C540	November 9, 2009	Darwin 10.2	About the Mac OS X v10.6.2 Update	Mac OS X v10.6.2 Update
10.6.3	10D573	March 29, 2010	Darwin 10.3	About the Mac OS X v10.6.3 Update	Mac OS X v10.6.3 Update
	10D575			Second retail DVD release	N/A
	10D578	April 13, 2010		About the Mac OS X v10.6.3 Update; v1.1	Mac OS X v10.6.3 v1.1 Update (Combo)

Mac OS X Server includes these features and other server-related features. Apple initially stated that Server would include ZFS support, but mention of this feature later disappeared from Apple's website and it was not included in the final release over licensing issues.^[60]
On Monday, 11 May 2009, after build 10A354, Apple issued a code freeze on Snow Leopard's APIs.^[61]

http://en.wikipedia.org/wiki/Mac_OS_X_Snow_Leopard
06/04/10

Safari Web Browser

2010-06-03T08:52:00.000-04:00

Safari is a graphical web browser developed by Apple and included as part of the Mac OS X operating system. First released as a public beta on January 7, 2003^[1] on the company's Mac OS X operating system, it became Apple's default browser beginning with Mac OS X v10.3 "Panther." Safari is also the native browser for the iPhone OS. A version of Safari for the Microsoft Windows operating system, first released on June 11, 2007, supports Windows XP, Windows Vista, and Windows 7.^[2] The latest stable release of the browser is 4.0.5, which is available as a free download for both Mac OS X and Microsoft Windows. As of 2010, Safari was either the third or fourth most widely used browser, tied with Google Chrome.^[3]

[hide]

[edit] History and development

[edit] Safari 1

On January 7, 2003, at Macworld San Francisco, Steve Jobs announced that Apple had developed their own web browser, called Safari. It was based on Apple's internal fork of the KHTML rendering engine, called WebKit.^[7] Apple released the first beta version for OS X that day. A number of official and unofficial beta versions followed, until version 1.0 was released on June 23, 2003. Initially only available as a separate download for Mac OS X v10.2, it was included with the Mac OS X v10.3 release on October 24, 2003 as the default browser, with Internet Explorer for Mac included only as an alternative browser.
The last version of Safari to support Mac OS X v10.2 is Safari 1.0.3, released on August 13, 2004. The last version to support Mac OS X v10.3 is 1.3.2, released January 12, 2006.

[edit] Safari 2

In April 2005, Dave Hyatt, one of the Safari developers at Apple, documented his progress in fixing specific bugs in Safari, thereby enabling it to pass the Acid2 test developed by the Web Standards Project. On April 27, 2005, he announced that his development version of Safari now passed the test, making it the first web browser to do so.^[8]
Safari 2.0 was released on April 29, 2005 as the only web browser included with Mac OS X v10.4. This version was touted by Apple as possessing a 1.8x speed boost over version 1.2.4, but did not yet include the Acid2 bug fixes. The necessary changes were not initially available to end-users unless they downloaded and compiled the WebKit source code themselves or ran one of the nightly automated builds available at OpenDarwin.org.^[9] Apple eventually released version 2.0.2 of Safari, which included the modifications required to pass Acid2, on October 31, 2005.
In June 2005, after some criticism from KHTML developers over lack of access to change logs, Apple moved the development source code and bug tracking of WebCore and JavaScriptCore to OpenDarwin.org. WebKit itself was also released as open source. The source code for non-renderer aspects of the browser, such as its GUI elements, remains proprietary.
The final stable version of Safari 2, Safari 2.0.4, was released on January 10, 2006 for Mac OS X. It was only available as part of Mac OS X Update 10.4.4. This version addresses layout and CPU usage issues, among others.^[10] Safari 2.0.4 was the last version to be released exclusively on Mac OS X.

[edit] Safari 3

On January 9, 2007, at Macworld SF, Jobs announced Apple's iPhone, which would use a mobile version of the Safari browser.^[11]
On June 11, 2007, at the Apple Worldwide Developers Conference, Jobs announced Safari 3 for Mac OS X v10.5, Windows XP, and Windows Vista. During the announcement, he ran a benchmark based on the iBench browser test suite comparing the most popular Windows browsers,^[12] hence claiming that Safari was the fastest browser. Later third-party tests of HTTP load times would support Apple's claim that Safari 3 was indeed the fastest browser on the Windows platform in terms of initial data loading over the Internet, though it was found to be only negligibly faster than Internet Explorer 7 and Mozilla Firefox when loading static content from local cache.^[13]
The initial Safari 3 beta version for Windows, released on the same day as its announcement at WWDC 2007, had several known bugs^[14] and a zero day exploit that allowed remote execution.^[15] The addressed bugs were then corrected by Apple three days later on June 14, 2007, in version 3.0.1 for Windows. On June 22, 2007, Apple released Safari 3.0.2 to address some bugs, performance issues and other security issues. Safari 3.0.2 for Windows handles some fonts that are missing in the browser but already installed on Windows computers, such as Tahoma, Trebuchet MS, and others.
The iPhone was formally released on June 29, 2007. It includes a version of Safari based on the same WebKit rendering engine as the desktop version, but with a modified feature set better suited for a mobile device. The version number of Safari as reported in its user agent string is 3.0,^[16] in line with the contemporary desktop versions of Safari.
The first stable, non-beta release of Safari for Windows, Safari 3.1, was offered as a free download on March 18, 2008. In June 2008, Apple released version 3.1.2,^[17]^[18] addressing a security vulnerability in the Windows version where visiting a malicious web site could force a download of executable files and execute them on the user's desktop.^[19]
Safari 3.2, released on November 13, 2008, introduced anti-phishing features and Extended Validation Certificate support. The final version of Safari 3 is 3.2.3, released on May 12, 2009.

[edit] Safari 4

On June 2, 2008, the WebKit development team announced SquirrelFish,^[20] a new JavaScript engine that vastly improves Safari's speed at interpreting scripts.^[21] The engine is one of the new features in Safari 4, released to developers on June 11, 2008. The new JavaScript engine quickly evolved into SquirrelFish Extreme, featuring even further improved performance over SquirrelFish,^[22] and was eventually marketed as Nitro. A public beta of Safari 4 was released on February 24, 2009, with new features such as the Top Sites tool (similar to Opera's Speed Dial feature), which displays the user's most visited sites on a 3D wall.^[23] Cover Flow, a feature of Mac OS X and iTunes, was also implemented in Safari. In the public beta versions, tabs were placed in the title bar of the window, similar to Google Chrome. The tab bar was moved back to its original location, below the URL bar, in the final release.^[24] The Windows version adopted a native Windows theme, rather than the previously employed Mac OS X-style interface.
On June 8, 2009, Safari 4 was officially released. Safari 4.0.1 was released for Mac on June 17 and fixed problems with Faces in iPhoto '09. Safari 4 in Mac OS X v10.6 "Snow Leopard" has 64-bit support, which can make JavaScript loading up to 50% faster. It also has built-in crash resistance unique to Snow Leopard; crash resistance will keep the browser intact if a plug-in like Flash player crashes, such that the other tabs or windows will be unaffected.^[25] Safari 4.0.4, released on November 11, 2009 for both OS X and Windows, further improves JavaScript performance.^[26]
Safari was one of the twelve browsers offered to EU users of Microsoft Windows in 2010. It is also one of the 5 browsers displayed on the first page of browser choices along with Chrome, Firefox, Internet Explorer and Opera.^[27]^[28]

[edit] Future development

On April 9, 2010 Apple announced WebKit2.^[29] This may be used in a future version of Safari.
"WebKit2 is designed from the ground up to support a split process model, where the Web content (JavaScript, HTML, layout, etc) lives in a separate process," wrote Apple developer Anders Carlsson to WebKit's public mailing list on April 8, 2010. "This model is similar to what Google Chrome offers, with the major difference being that we have built the process split model directly into the framework, allowing other clients to use it."^[29]
The "process split" model to which Carlsson refers is the architecture that enables processes spawned by the browser, including add-ons and Web apps, to be run as separate processes in the operating system while still being protected by the browser's sandbox. Google's Chromium team developed the first such model in working form for its Chrome browser.^[30]^[31]

[edit] Features

Safari offers numerous features, including:

Ability to save webpage clips for viewing on the Apple Dashboard (Mac OS X only)
A resizable web-search box in the toolbar which uses Google on the Mac and either Google or Yahoo! on Windows
Automatic filling in of web forms ("autofill")
Bookmark integration with Address Book
Bookmark management
Built-in password management via Keychain (Mac OS X only)
History and bookmark search
Expandable text boxes
ICC color profile support
Inline PDF viewing (Mac OS X only)
iPhoto integration (Mac OS X only)
Mail integration (Mac OS X only)
Pop-up ad blocking
Private browsing
Quartz-style font smoothing
Spell checking
Subscribing to and reading web feeds
Support for CSS 3 web fonts
Support for CSS animation
Support for HTML5
Support for Transport Layer Security protocol (version unknown)
Tabbed browsing
Text search
Web Inspector, a DOM Inspector-like utility that lets users and developers browse the Document Object Model of a web page^[32]

Safari's Web Inspector, showing the DOM tree for this page.

On Mac OS X, Safari is a Cocoa application.^[33] It uses Apple's WebKit for rendering web pages and running JavaScript. WebKit consists of WebCore (based on Konqueror's KHTML engine) and JavaScriptCore (originally based on KDE's JavaScript engine, named KJS). Like KHTML and KJS, WebCore and JavaScriptCore are free software and are released under the terms of the GNU Lesser General Public License. Some Apple improvements to the KHTML code are merged back into the Konqueror project. Apple also releases additional code under an open source 2-clause BSD-like license.
It includes a built-in web feed aggregator that supports the RSS and Atom standards. Other features include Private Browsing (a mode in which no record of information about the user's web activity is retained by the browser),^[34] the ability to archive web content in the proprietary Webarchive format, the ability to e-mail complete web pages directly from a browser menu, and the ability to search bookmarks.
Beginning with Safari 4, the address bar has been completely revamped:

Safari 4 on Windows XP

The blue inline progress bar is replaced with a spinning bezel and a loading indicator attached to it.
The button to add a bookmark is now attached to the address bar by default.
The reload/stop button is now superimposed on the right end of the address bar.

These modifications make Safari on Mac OS X and Windows look more similar to Safari on iPhone than previous versions.
In addition, Safari 4 includes the following new features:

Completely passes the Acid3 standards test
Cover Flow browsing for History and Bookmarks
Improved developer tools, including Web Inspector, CSS element viewing, JavaScript debugger and profiler, offline table and database management with SQL support, and resource graphs
Nitro JavaScript engine that executes JavaScript up to eight times faster than Internet Explorer 8 and more than four times faster than Firefox 3^[35]
Native Windows look on Windows (Aero, Luna, Classic, etc., depending on OS and settings) with standard Windows font rendering and optional Apple font rendering
Support for CSS image retouching effects
Support for CSS Canvas
Speculative loading, where Safari loads the documents, scripts, and style information that are required to view a web page ahead of time
Support for HTML5
Top Sites, which displays up to 24 thumbnails of a user's most frequently-visited pages on startup

Safari on the iPhone and iPod Touch

[edit] iPhone OS-specific features

iPhone OS-specific features for Safari enable:

Bookmarking links to particular pages as "Web Clip" icons on the Home screen.
MDI-style browsing (with up to 8 pages open concurrently, limited by cache storage).
Opening specially-designed pages in full-screen mode.
Pressing on an image for 3 seconds to save it to the photo album.
Support for HTML5 new input types.

[edit] System requirements

The latest version of Safari requires either a Mac running Mac OS X v10.4 or later, or a PC running Windows XP SP2, Windows Vista, or Windows 7. Official minimum hardware requirements are any Intel processor or a PowerPC G3, G4, or G5 with 256 MB of RAM for Mac or a 500 MHz Pentium processor with 256 MB of RAM for Windows. Cover Flow and Top Sites require a graphics card that is Quartz Extreme-compatible with 16 MB or more video memory for Mac or DirectX 9-compatible with 32 MB or more video memory for Windows.^[36]

[edit] 64-bit builds

The version of Safari included in Mac OS X v10.6 is now compiled in 64-bit. Apple claims that running Safari in 64-bit mode will increase rendering speeds by up to 50%. However, there is currently no 64-bit build for Mac OS X v10.5 or older, Windows XP, Windows Vista, or Windows 7.

[edit] Criticism

[edit] Distribution through Apple Software Update

An earlier version of Apple Software Update (bundled with Safari, QuickTime, and iTunes for Microsoft Windows) selected Safari for installation from a list of Apple programs to download by default, even when a pre-existing installation of Safari was not detected on a user's machine. John Lilly, CEO of Mozilla, stated that Apple's use of its updating software to promote its other products was "a bad practice and should stop." He argued that the practice "borders on malware distribution practices" and "undermines the trust that [software companies are] all trying to build with users."^[37] Apple spokesman Bill Evans responded to Lilly's statement, saying that Apple was only "using Software Update to make it easy and convenient for both Mac and Windows users to get the latest Safari update from Apple."^[38] Apple also released a new version of Apple Software Update that puts new software in its own section, though still selected for installation by default.^[39] In a newer update, Apple Software Update no longer selected new installation items in the new software section by default (as of late 2008).^{[citation needed]}
On September 22, 2009, Apple once again checked "Install Safari 4" as a default setting with their update to iTunes v9.0.1.^{[citation needed]} As of September 30, 2009, Safari is not a pre-selected application in Apple Software Update when it is not already installed.^[40]

[edit] Browser exploits

In the PWN2OWN contest at the 2008 CanSecWest security conference in Vancouver, British Columbia, a successful exploit of Safari caused Mac OS X to be the first OS to fall in a hacking competition. Participants competed to find a way to read the contents of a file located on the user's desktop, in one of three operating systems: Mac OS X Leopard, Windows Vista SP1, and Ubuntu 7.10. On the second day of the contest, when users were allowed to physically interact with the computers (the prior day permitted only network attacks), Charlie Miller compromised Mac OS X through an unpatched vulnerability of the PCRE library used by Safari.^[41] Miller had been aware of the flaw prior to the beginning of the conference and worked to exploit it unannounced.^[41] The exploited vulnerability was patched in Safari 3.1.1, among other flaws.^[42]
In the 2009 PWN2OWN contest, Charlie Miller performed another successful exploit of Safari to hack into a Mac. Miller again acknowledged that he had advance knowledge of the security flaw prior to the competition, and had done considerable research and preparation work on the exploit.^[43]^[44] Apple released a patch for this exploit and others on May 12, 2009 in Safari 3.2.3.^[45]^[46]

[edit] Software license agreement

The original software license agreement for Safari on Windows was unusually restrictive for several months,^[47] reading in part:

This License allows you to install and use one copy of the Apple Software on a single Apple-labeled computer at a time.^[48]

As most personal computers running Windows are not Apple-labeled computers, it was impossible for most Windows users to use the software and abide by the license agreement, with the exception of Intel-based Mac computers running Windows. Within hours of the story breaking about the long-unnoticed anomaly, Apple changed the agreement as posted on their website to read:^[48]

This license allows you to install and use one copy of the Apple Software on each computer owned or controlled by you.^[49]

However, the Safari installer was not immediately updated and still contained the old license.^[50] Later installers include corrected copies of the license.

http://en.wikipedia.org/wiki/Safari_web_browser
06/02/10

Windows Vista Firewall

2010-06-03T08:51:00.000-04:00

Windows Firewall is the firewall service included with desktop and server releases of Microsoft Windows from Windows XP and Windows Server 2003 onwards. Prior to the release of Windows XP Service Pack 2 in 2004, it was known as Internet Connection Firewall.

[hide]

[edit] Overview

When Windows XP was originally shipped in October 2001, it included a limited firewall called "Internet Connection Firewall". It was disabled by default due to concerns with backward compatibility, and the configuration screens were buried away in network configuration screens that many users never looked at. As a result, it was rarely used. In mid-2003, the Blaster worm attacked a large number of Windows machines, taking advantage of flaws in the RPC Windows service.^[1] Several months later, the Sasser worm did something similar. The ongoing prevalence of these worms through 2004 resulted in unpatched machines being infected within a matter of minutes.^[1] Because of these incidents, as well as other criticisms that Microsoft was not being active in protecting customers from threats, Microsoft decided to significantly improve both the functionality and the interface of Windows XP's built-in firewall, and rebrand it as, simply, "Windows Firewall".
Security log capabilities are included, which can record IP addresses and other data relating to connections originating from the home or office network or the Internet. It can record both dropped packets and successful connections. This can be used, for instance, to track every time a computer on the network connects to a website. This security log is not enabled by default; the administrator must enable it.^[2]

[edit] Versions

[edit] Windows XP

Windows Firewall settings in Windows XP Service Pack 2

Windows Firewall was first introduced as part of Windows XP Service Pack 2. Every type of network connection, whether it is wired, wireless, VPN, or even FireWire, has the firewall enabled by default, with some built-in exceptions to allow connections from machines on the local network. It also fixed a problem whereby the firewall policies would not be enabled on a network connection until several seconds after the connection itself was created, thereby creating a window of vulnerability.^[3] A number of additions were made to Group Policy, so that Windows system administrators could configure the Windows Firewall product on a company-wide level. XP's Windows Firewall cannot block outbound connections; it is only capable of blocking inbound ones.
Windows Firewall turned out to be one of the two most significant reasons (the other being DCOM activation security)^[4] that many corporations did not upgrade to Service Pack 2 in a timely fashion. Around the time of SP2's release, a number of Internet sites were reporting significant application compatibility issues, though the majority of those ended up being nothing more than ports that needed to be opened on the firewall so that components of distributed systems (typically backup and antivirus solutions) could communicate.

[edit] Windows Vista

Windows Vista significantly improves the firewall to address a number of concerns around the flexibility of Windows Firewall in a corporate environment:^[5]

A new management console snap-in named Windows Firewall with Advanced Security which provides access to many advanced options, and enables remote administration. This can be accessed via Start -> Control Panel -> Administrative Tools -> Windows Firewall with Advanced Security, or by running "wf.msc"
IPv6 connection filtering.
Outbound packet filtering, reflecting increasing concerns about spyware and viruses that attempt to "phone home". Outbound rules are configured using the management console. Notifications are not shown however for outbound connections.
With the advanced packet filter, rules can also be specified for source and destination IP addresses and port ranges.
Rules can be configured for services by its service name chosen by a list, without needing to specify the full path file name.
IPsec is fully integrated, allowing connections to be allowed or denied based on security certificates, Kerberos authentication, etc. Encryption can also be required for any kind of connection.
Improved interface for managing separate firewall profiles. Ability to have three separate firewall profiles for when computers are domain-joined, connected to a private network, or connected to a public network (XP SP2 supports two profiles—domain-joined and standard). Support for the creation of rules for enforcing server and domain isolation policies.

[edit] Windows Server 2008

Windows Server 2008 R1 contains the same firewall as Windows Vista. The firewall in Windows Server 2008 R2 and Windows 7 contains some improvements, such as multiple active profiles.^[6]

^{http://en.wikipedia.org/wiki/Windows_Firewall}
^06/02/10

Opera Web Browser

2010-06-03T08:24:00.000-04:00

Opera is a web browser and Internet suite developed by Opera Software. The browser handles common Internet-related tasks such as displaying web sites, sending and receiving e-mail messages, managing contacts, chatting on IRC, downloading files via BitTorrent, and reading Web feeds. Opera is offered free of charge for personal computers and mobile phones.
Features include tabbed browsing, page zooming, mouse gestures, and an integrated download manager. Its security features include built-in phishing and malware protection, strong encryption when browsing secure Web sites, and the ability to easily delete private data such as HTTP cookies.
Opera runs on a variety of personal computer operating systems, including Microsoft Windows, Mac OS X, Linux, and FreeBSD. The Desktop Team recently dropped support for Solaris.^[7] Evaluations of Opera have been largely positive, and Opera has innovated many key features of modern browsers.^[8]^[9] Despite these factors, Opera has captured only a small fraction of the worldwide personal computer browser market. It does, though, have a stronger market share on mobile devices such as mobile phones, smartphones, and personal digital assistants. Editions of Opera are available for devices using the BlackBerry, Symbian, Windows Mobile, Android, and iPhone operating systems, as well as Java ME-enabled devices.^[10]^[11]^[12] Approximately 120 million mobile phones have been shipped with Opera.^[13] Opera is the only commercial web browser available for the Nintendo DS and Wii gaming systems. Some television set-top boxes use Opera. Adobe Systems has licensed Opera technology for use in the Adobe Creative Suite.^[14]^[15]

[hide]

Opera began in 1994 as a research project at Telenor, the largest Norwegian telecommunications company. In 1995, it branched out into a separate company named Opera Software ASA.^[16] Opera was first released publicly with version 2.0 in 1996,^[17] which only ran on Microsoft Windows.^[18] In an attempt to capitalize on the emerging market for Internet-connected handheld devices, a project to port Opera to mobile device platforms was started in 1998.^[18] Opera 4.0, released in 2000,^[17] included a new cross-platform core that facilitated creation of editions of Opera for multiple operating systems and platforms.^[19]
Up to this point, Opera was trialware and had to be purchased after the trial period ended. Version 5.0 (released in 2000) saw the end of this requirement. Instead, Opera became ad-sponsored, displaying advertisements to users who had not paid for it.^[20] Later versions of Opera gave the user the choice of seeing banner ads or targeted text advertisements from Google. With version 8.5 (released in 2005) the advertisements were removed entirely and primary financial support for the browser came through revenue from Google (which is by contract Opera's default search engine).^[21]
Among the new features introduced in version 9.1 (released in 2006) was fraud protection using technology from GeoTrust, a digital certificate provider, and PhishTank, an organization that tracks known phishing web sites.^[22] This feature was further improved and expanded in version 9.5, when GeoTrust was replaced with Netcraft, and malware protection from Haute Secure was added.^[23]
Also in 2006, editions of Opera were made and released for Nintendo's DS and Wii gaming systems.^[24]^[25]^[26]^[27] Opera for the Wii, called the Internet Channel, was free to download from its release on 12 April 2007^[28] until 30 June 2007. After that date, Wii users had to pay 500 Wii Points (about US$5^[29]) to download it.^[30] As of 2 September 2009, it is again free to download. Users who previously paid to download are offered a NES game of their choice of the same value.^[31]^[32] The Nintendo DS Browser is not free; it is sold as a physical DS game cartridge. The DSi has an Internet Channel that can be downloaded for free from the DSi shop.^[33]
Opera was one of the twelve browsers offered to European Economic Area users of Microsoft Windows in 2010.^[34]
A new JavaScript engine called Carakan, after the Javanese script, was introduced with version 10.50.^[35] According to Opera Software, Carakan is more than seven times faster in SunSpider than Opera 10.10 with Futhark on Windows, which has since been more or less confirmed by other sources after its official pre-alpha release in December 2009.^[36]^[37]^[38] Also introduced was Opera's vector graphics library, Vega, which handles all of the browser's rendering. This allows platform specific rendering code to be replaced with code for Vega, which makes it easier to deploy across platforms; aids Opera's implementation of some advanced CSS3 properties, such as backgrounds and borders; and also allows hardware acceleration with optional OpenGL and Direct3D backends.^[39] An initial Alpha of Opera 10.60 was released on the 31st of May, 2010.

[edit] Features

Main article: Features of the Opera web browser

One set of third-party speed tests ^[40] ^[41] ^[42] concluded that Opera 9.5 was indeed faster than Internet Explorer 7 and prerelease versions of Firefox 3 and Safari 3.^[43] Technology website ZDNet's speed tests in early 2008 showed that out of Internet Explorer 7, Safari 3, and pre-release versions of Firefox 3 and Opera 9.5, Opera was the fastest in some areas, but the only browser that Opera clearly outperformed was Internet Explorer.^[44] However, as of Opera 10.50 (codenamed Evenes)—which has been released for Windows and Mac OS X, and currently is in the pre-release stage for UNIX—features a new JavaScript engine (codenamed Carakan), as well as a new vector graphics library (codenamed Vega), which together significantly increase Opera's overall rendering speed.^[36]^[45]
Opera includes built-in tabbed browsing, ad blocking, fraud protection, a download manager and BitTorrent client, a search bar, and a web feed aggregator. Opera also comes with an e-mail client called Opera Mail and an IRC chat client built in.^[46]
Opera includes a "Speed Dial" feature, which allows the user to add up to 25 links (or more, by editing the speeddial.ini file) shown in thumbnail form in a page displayed when a new tab is opened. Thumbnails of the linked pages are automatically generated and used for visual recognition on the Speed Dial page or can be modified using Opera Image Dial Generator. Once set up, this feature allows the user to more easily navigate to the selected web pages.^[47] Note that editing the speeddial.ini located in the directory file (which is in an OS-dependent location) of Opera gives the user better control of the look of the new tab. It gives the ability to edit the number of columns and rows separately, and recently the opacity of thumbnails for better visibility of the background image.
Opera supports Opera Widgets, small web applications that start from within Opera. Alongside Widgets, "User JavaScript" may be used to add custom JavaScript to web pages. Greasemonkey support is limited, and there is no interface to manage scripts or toggle 'Greasemonkey-on' functionality.
Opera is extensible in a third way via plug-ins, relatively small programs that add specific functions to the browser.^[48] However, Opera limits what plug-ins can do and does not support full-fledged third-party extensions to the browser. Opera does this as a quality assurance measure, so that third-party extensions cannot introduce bugs.^[49]

[edit] Usability and accessibility

Sample mouse gestures in Opera
	Back: hold down right mouse button, move mouse left, and release or hold the right button down and click the left button
	Forward: hold down right mouse button, move mouse right, and release or hold the left button down and click the right button
	New tab: hold down right mouse button, move mouse down, and release. Clicking a link with the middle mouse button produces a similar effect, but the new tab is opened in the background instead of becoming the active tab.

Opera was designed with a commitment to computer accessibility for users who have visual or motor impairments. As a multimodal browser, it also caters to a wide variety of personal preferences in the user interface.
It is possible to control nearly every aspect of the browser using only the keyboard,^[50] and the default keyboard shortcuts can be modified to suit the user.^[51]^[52] It is the only major browser to include support for spatial navigation. Opera also includes support for mouse gestures,^[53] patterns of mouse movement that trigger browser actions such as "back" or "refresh".^[54]
Page zooming allows text, images and other content such as Adobe Flash Player, Java platform and Scalable Vector Graphics to be increased or decreased in size (20% to 1,000%) to help those with impaired vision. The user may also specify the fonts and colors for web pages, and even override the page's CSS styling as well. This can be useful for making sites appear in high contrast or in more readable fonts.^[55]
Voice control, co-developed with IBM, allows control of the browser without the use of a keyboard or mouse.^[56]^[57] It can also read aloud pages and marked text.^[46]

[edit] Privacy and security

Opera has several security features visible to the end user. One is the option to delete private data, such as HTTP cookies, the browsing history, and the cache, with the click of a button. This lets users erase personal data after browsing from a shared computer.^[58]
When visiting a secure web site, Opera encrypts data using either SSL 3 or TLS,^[59]^[60] both of which are highly secure encryption protocols. It then adds information about the site's security to the address bar. It will also check the web site that is being visited against blacklists for phishing and malware, and warn if it matches any of these lists. This behavior is enabled by default, but the user may opt to not make such checks automatically. If this check is disabled, the user can still check sites individually by opening a Page Info dialog.^[61]
The user can protect every saved password stored in Opera with a master password. This prevents malware from accessing those passwords unless the master password is known. To catch security flaws and other software bugs before they are exploited or become a serious problem, the Opera Software company maintains a public web form where users can submit bug reports.^[62] According to Secunia, a computer security service provider, the mean average of unpatched vulnerabilities in the last 365 days is 0.01. This stands in contrast to Internet Explorer (38.3), Firefox (5.77), and Safari (1.54).^[63]
In January 2007, Asa Dotzler of the competing Mozilla Corporation accused the Opera Software company of downplaying information about security vulnerabilities in Opera that were fixed in December 2006. Dotzler claimed that users were not clearly informed of security vulnerabilities present in the previous version of Opera, and thus they would not realize that they needed to upgrade to the latest version or risk being exploited.^[64] Opera responded to these accusations the next day.^[65]

[edit] Standards support

Opera was one of the first browsers to support Cascading Style Sheets (CSS), now a major building block of web design.^[66] Today, Opera supports many web standards, including CSS 2.1, HTML 4.01, XHTML 1.1, XHTML Basic, XHTML Mobile Profile, XHTML+Voice, WML 2.0, XSLT, XPath, XSL-FO, ECMAScript 3 (JavaScript), DOM 2, XMLHttpRequest, HTTP 1.1, TLS 1.2^[67], Unicode, SVG 1.1 Basic, SVG 1.1 Tiny, GIF89a, JPEG, and full support for PNG, including alpha transparency.^[68] Since version 9, Opera passes the Acid2 test, a test of whether or not a browser properly supports certain web standards. Opera was the second or fourth web browser to pass the test (depending on opinions regarding hiding the scrollbar)^[69] and the first Windows browser to do so. Opera 10.5+ achieves a score of 100/100 on the Acid3 test^[70] which is primarily focused on DOM and JavaScript standards compliance.
Opera also has a fast and standards compliant JavaScript engine named Carakan, which in Sputnik conformance tests (written by Google) failed only in 78 cases. For a comparison with other browsers: Safari 159, Chrome 218, Firefox 259, Internet Explorer 463 (all current stable versions as of May 4, 2010).^[71]

[edit] Opera Unite

Opera Unite Logo

Opera Unite is an extensible framework that allows for several web services (referred to as "Applications"^[72]) to be hosted from the user's computer, including a web server for hosting a site, file and photo sharing, a chat room, and streaming media. Opera ASA has released an API to create new or improved applications for the Opera Unite Platform, and many have already done so. An Opera Unite user's applications run on a domain associated with their Opera Community account, and are accessible from any web browser. For these applications to be accessed, the computer and the Opera Browser hosting the applications must both be running.
The included API uses HTML, CSS, client-side ECMAScript and a new server-side JavaScript technology with local file access and persistent storage. Unite Applications are packaged according to the W3C Widgets 1.0 specification. Opera also provides a vetted facility for developers to upload these user-created applications.^[73]
Unite has been included standard since version 10.10.^[74]

[edit] Other editions

Aside from the main edition of Opera for personal computers, editions of Opera are available for a variety of devices. All are based on the same core,^[75] but there is some variation in the features offered and the design of the user interface.

[edit] Smartphones and PDAs

Main article: Opera Mobile

Opera Mobile can be used on smartphones such as the Nokia 6630.

Opera Mobile is an edition of Opera designed for smartphones and personal digital assistants (PDAs). The first version of Opera Mobile was released in 2000 for the Psion Series 7 and NetBook, with a port to the Windows Mobile platform coming in 2004.^[76]^[77] Today, Opera Mobile is available for a variety of devices that run the Windows Mobile, S60 platform, or UIQ operating systems.^[78]
Users may try Opera Mobile free for 30 days, but beyond that it costs US$24.^[79] Devices that use the UIQ 3 operating system, such as the Sony Ericsson P990 and Motorola RIZR Z8, come pre-installed with Opera Mobile, the price of Opera Mobile being included in the price of the phone.^[78]
One of Opera Mobile's major features is the ability to dynamically reformat web pages to better fit the handheld's display using small screen rendering technology.^[80] Alternatively, the user may use page zooming for a closer or broader look.^[81] However, like previous versions of Opera for personal computers, Opera Mobile's user interface has come under fire for being difficult to use or customize.^[82]^[83]

[edit] Mobile phones

Main article: Opera Mini

When a user browses the web using Opera Mini, the request is sent via the General Packet Radio Service (GPRS) to one of the Opera Software company's servers, which retrieves the web page, processes it, compresses it, and sends it back to the user's mobile phone.

Opera Mini, offered free of charge, is designed primarily for mobile phones, but also for smartphones and personal digital assistants. It uses the Java ME platform and consequently requires that the mobile device be capable of running Java ME applications. The browser began as a pilot project in 2005.^[84] After limited releases in Europe,^[85]^[86] it was officially launched worldwide on 24 January 2006.^[87]
Opera Mini requests web pages through the Opera Software company's servers, which process and compress them before relaying the pages back to the mobile phone.^[84]^[88] This compression process reduces bandwidth use by up to 90%^[89] and the pre-processing smooths compatibility with web pages not designed for mobile phones.^[90]
In March 2010, Opera Software has launched a new beta version of its Mini browser for mobile phones running on the Google's open source Android platform.The company claims that the Opera Mini 5 is capable of compressing data by up to 90 per cent before sending content to the phone, resulting in improved page-load times and speed.^[91]
Opera Software has launched a native version of Opera Mini 5 beta for Windows Mobile 5- and 6-based handsets, which traditionally requires Java. The Mini 5 for Windows mobile phone included the same feature set as its Java-based version.
On April 13, 2010, Opera Mini was officially approved as a free download for iPhone (and iPod Touch) on Apple's App Store.^[92]

[edit] Nintendo DS

Main article: Nintendo DS & DSi Browser

The Nintendo DS

The Nintendo DS Browser is an edition of Opera for the Nintendo DS handheld gaming system. The Nintendo DS Browser was released in Japan on 24 July 2006,^[93] in Europe on 6 October 2006,^[94] and in North America on 4 June 2007.^[95] It is sold as a physical game cartridge for US$30.^[33]
The Nintendo DS Browser includes the same small screen rendering and page zooming technology present in Opera Mobile.^[25]^[81] It also includes handwriting recognition software and an on-screen keyboard to enable user input. Additionally, Nintendo partnered with Astaro Internet Security to provide web filtering for the Nintendo DS Browser. The technology is simply a professionally maintained proxy server that blocks web sites related to pornography, discrimination, security hacking, software piracy, violence, gambling, illegal drugs, alcohol, tobacco, dating, weapons, abortion, and other content that Nintendo deems objectionable.^[96] Users can configure the Nintendo DS Browser to receive web pages through this proxy server, and this setting can be password-protected (by a parent, for example) to prevent circumvention.^[97]
In August 2007, the Nintendo DS Browser was quietly discontinued in North America,^[33]^[98] although it is still available from Nintendo's online store.^[99] Instead, Opera is available on the Nintendo DSi through the DSi Shop.^[100]

[edit] Wii

Main article: Internet Channel

Nintendo's Wii console

On 10 May 2006, the Opera Software company announced that it was partnering with Nintendo to provide a web browser for Nintendo's Wii gaming console.^[24]^[25]^[26]^[27] Opera for the Wii, called the Internet Channel, was free to download from its release on 12 April 2007^[28] until 30 June 2007. After that date, Wii users had to pay 500 Wii Points (US$5^[29]) to download it.^[30] However, in late August / early September of the year 2009, the Internet Channel was once again available to download for free and those who paid for the service had their Wii Points returned in the form of a free NES virtual console game.^[101]
Scott Hedrick, an executive of the Opera Software company, explained that the Wii browser was designed to suit a "living room environment".^[102] In contrast to Opera's appearance on computer monitors, fonts are larger and the interface is simplified for easier use.^[102] Notwithstanding the changes in design, the Wii browser supports the same web standards as the desktop version of Opera 9,^[102] including passing the Acid2 test.^[103]

[edit] Market adoption

The usage share of web browsers.
Source: Median values from summary table. Internet Explorer (53.26%; Usage by version number) Mozilla Firefox (31.60%; Usage by version number) Google Chrome (8.00%) Safari (5.40%) Opera (1.82%) Other (0.89%)

Statistics reference: Usage share of web browsers

In July 2009, usage data on English-language sites showed Opera's share of the browser market as being just around 2%.^[104] The browser has seen more success in Europe, including about 43% market share in 2009 in Ukraine, 36% Russia, and 8-11% in Poland, Latvia, Lithuania, and the Czech Republic.^[105]
In September 2009, Opera broke its previous download records when Opera 10 was released and was recorded to be downloaded 10 million times during the first week of release.^[106]
Since its first release in 1996, the browser has had limited success on personal computers. It has had more success in the area of mobile browsing, with product releases for a variety of platforms.^[107] Approximately 40 million mobile phones have shipped with a copy of Opera pre-installed.^[108]
In addition to mobile phones, smartphones, and personal digital assistants, Opera has found a place with Nintendo's Wii and DS gaming systems. It is used on some television set-top boxes as well.^[109] In 2005, Adobe Systems opted to integrate Opera's layout engine, Presto, into its Adobe Creative Suite applications. Opera technology is now found in Adobe GoLive, Adobe Photoshop, Adobe Dreamweaver, and other components of the Adobe Creative Suite.^[14]^[15] Opera's layout engine is also found in Virtual Mechanics SiteSpinner Pro.^[110]

[edit] Reception

Critical reception of Opera has been largely positive,^[111]^[112]^[113] although it has been criticized for website compatibility issues.^[114]^[115] According to one of Opera's competitors, this is partly because developers do not test web sites with Opera due its lack of market share.^[115] Because of this issue, Opera 8.01 and higher have included workarounds to help certain popular but problematic web sites display properly.^[116]^[117] Notwithstanding other criticism, when Nintendo chose in 2006 to adopt Opera as the web browser for its Wii and Nintendo DS gaming systems, a Nintendo representative explained:

For our Wii console launch in 2006, we required a browser that was fast and secure with support for the latest standards including AJAX. Opera proved perfect for our purposes and is an exceptional addition to both the Nintendo DS and the Wii console.
—Genyo Takeda, senior managing director and general manager, Integrated Research & Development Division , Nintendo^[26]

http://en.wikipedia.org/wiki/Opera_Web_Browser
06/02/10

Windows Vista Switch between windows

2010-06-03T08:21:00.000-04:00

Fast user switching is a feature on some modern multi-user operating systems such as Windows XP, Windows Vista, Windows 7, Mac OS X, Linux.^[1] It allows users to switch between user accounts on a single PC without quitting applications and logging out. Analogous functionality was first developed on consumer level hardware by the Xenix operating system which supported multiple virtual consoles. Linux, BSD, and most other PC Unixes adopted virtual terminals and further developed the user interfaces, including allowing users to optionally run separate graphical X Window System sessions.
Many free software environments, such as GNOME or KDE, support fast user switching with a drop menu, in a way analogous to OS X. For installations with older environments, the functionality must be enabled in the configuration file of the X display manager (for example GDM) then a hot key sequence such as CTRL-ALT-F8 is pressed. A separate login window will now appear and the second user can login (or even the first user again). Alternatively, in the default install, new X sessions can be started at will by using different display parameters to have them run in different virtual terminals (e.g. "startx -- :1" or "X :1 -query localhost"). Again, hot key sequences allow the user switching to take place.
Fast user switching may potentially introduce various security-related complications^{[citation needed]}, and is handled differently among operating systems, each having its advantages and disadvantages. One possibility, simple and secure, is that only the first user gets ownership of resources. A second option is to grant ownership of resources to each new user. The last one to log in takes ownership. A third is to allow all users access to shared resources. This is easier and more intuitive, but allows (for example) one user to record another user's conversation. In Windows, shared resources, such as sound, are available to all sessions. In Red Hat Linux, the default behavior is to give ownership of "console resources" to the first connected session, but it can share resources among groups of console users or be configured to manage console ownership differently.

[edit] Windows implementation

Fast user switching in Windows is based on Remote Desktop Services technology.^[2] In Windows XP, GINA which is a component of Winlogon, and with which fast user switching interacts, can be programmatically called to automate a fast user switch.^[3] A Powertoy known as Super fast user switcher was offered in 2002 by Microsoft. It allowed fast user switching using a keyboard hotkey (Win+Q) (similar to Alt-Tab) without even going to the Welcome screen. ^[4] It was later made unavailable when the original set of powertoys was replaced by updated versions but still works with Windows XP SP3 (32-bit) when running as administrator.
In Windows Vista, GINA is replaced by Credential Providers, however they do not support programatically initiating fast user switching.^[5]
In Windows XP, fast user switching is unavailable if the computer is on a domain network. However, it is available for domain computers starting with Windows Vista.
http://en.wikipedia.org/wiki/Fast_user_switching
06/02/10

What is the difference between a HDD and a external harddrive

2010-06-01T13:42:00.000-04:00

A hard disk drive^[2] (hard disk,^[3] hard drive,^[4] HDD) is a non-volatile storage device for digital data. It features one or more rotating rigid platters on a motor-driven spindle within a metal case. Data is encoded magnetically by read/write heads that float on a cushion of air above the platters, with modern storage capacity measured in gigabytes and terabytes.
The first hard disks were invented by IBM in 1956. They have fallen in size and cost over the years, displacing floppy disks in the late 1980s as the preferred long-term storage mechanism for personal computers. Most desktop systems today have standardized on the 3.5" form factor, and though mobile systems most often use 2.5" drives, both sizes operate on similar high-speed serial interfaces.

The neutrality of this section is disputed. Please see the discussion on the talk page. Please do not remove this message until the dispute is resolved. (May 2010)

Despite their utility, hard disk design introduces inherent performance compromises. The manipulation of sequential data depends upon the rotational speed of the platters and the data recording density. Because heat and vibration limit rotational speed, advancing density becomes the sole method to improve sequential transfer rates. While these advances exponentially increase storage capacity, the performance gains they enable are only linear. Performance relative to capacity in new generations of hard disks has therefore fallen with time. Operations on non-sequential data are further compromised by the overhead of moving the read/write heads to new positions. The more scattered the data, the more transfer rates suffer. The multi-layer caching structure of modern computers is a direct response to these limitations. As of 2010, the arrival of inexpensive non-volatile flash memory has made the continued dominance of hard disks in personal computing uncertain. Storage capacity has increased at a rate far in excess of the data requirements of common productivity applications. Media-streaming from distant servers continues to rise in popularity,^[5] concurrent with the appearance of portable devices that call for a level of power consumption, durability, and instant-access that a hard disk cannot provide. While the aggregate data demands of all users will continue to expand, future hard disk market share may shift to the enterprise sector.

[edit] History

Main article: History of hard disk drives

HDDs (introduced in 1956 as data storage for an IBM accounting computer)^[6] were originally developed for use with general purpose computers. During the 1990s, the need for large-scale, reliable storage, independent of a particular device, led to the introduction of embedded systems such as RAIDs, network attached storage (NAS) systems, and storage area network (SAN) systems that provide efficient and reliable access to large volumes of data. In the 21st century, HDD usage expanded into consumer applications such as camcorders, cellphones (e.g. the Nokia N91), digital audio players, digital video players, digital video recorders, personal digital assistants and video game consoles.

[edit] Technology

Diagram of a computer hard disk drive

HDDs record data by magnetizing ferromagnetic material directionally, to represent either a 0 or a 1 binary digit. They read the data back by detecting the magnetization of the material. A typical HDD design consists of a spindle that holds one or more flat circular disks called platters, onto which the data are recorded. The platters are made from a non-magnetic material, usually aluminum alloy or glass, and are coated with a thin layer of magnetic material, typically 10–20 nm in thickness — for reference, standard copy paper is 0.07–0.18 millimetre (70,000–180,000 nm) thick^[7] — with an outer layer of carbon for protection. Older disks used iron(III) oxide as the magnetic material, but current disks use a cobalt-based alloy. ^[8]

A cross section of the magnetic surface in action. In this case the binary data are encoded using frequency modulation.

The platters are spun at very high speeds. Information is written to a platter as it rotates past devices called read-and-write heads that operate very close (tens of nanometers in new drives) over the magnetic surface. The read-and-write head is used to detect and modify the magnetization of the material immediately under it. There is one head for each magnetic platter surface on the spindle, mounted on a common arm. An actuator arm (or access arm) moves the heads on an arc (roughly radially) across the platters as they spin, allowing each head to access almost the entire surface of the platter as it spins. The arm is moved using a voice coil actuator or in some older designs a stepper motor.
The magnetic surface of each platter is conceptually divided into many small sub-micrometre-sized magnetic regions, each of which is used to encode a single binary unit of information. Initially the regions were oriented horizontally, but beginning about 2005, the orientation was changed to perpendicular. Due to the polycrystalline nature of the magnetic material each of these magnetic regions is composed of a few hundred magnetic grains. Magnetic grains are typically 10 nm in size and each form a single magnetic domain. Each magnetic region in total forms a magnetic dipole which generates a highly localized magnetic field nearby. A write head magnetizes a region by generating a strong local magnetic field. Early HDDs used an electromagnet both to magnetize the region and to then read its magnetic field by using electromagnetic induction. Later versions of inductive heads included metal in Gap (MIG) heads and thin film heads. As data density increased, read heads using magnetoresistance (MR) came into use; the electrical resistance of the head changed according to the strength of the magnetism from the platter. Later development made use of spintronics; in these heads, the magnetoresistive effect was much greater than in earlier types, and was dubbed "giant" magnetoresistance (GMR). In today's heads, the read and write elements are separate, but in close proximity, on the head portion of an actuator arm. The read element is typically magneto-resistive while the write element is typically thin-film inductive.^[9]
HD heads are kept from contacting the platter surface by the air that is extremely close to the platter; that air moves at, or close to, the platter speed.^{[citation needed]} The record and playback head are mounted on a block called a slider, and the surface next to the platter is shaped to keep it just barely out of contact. It's a type of air bearing.
In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might be lost because of thermal effects. To counter this, the platters are coated with two parallel magnetic layers, separated by a 3-atom-thick layer of the non-magnetic element ruthenium, and the two layers are magnetized in opposite orientation, thus reinforcing each other.^[10] Another technology used to overcome thermal effects to allow greater recording densities is perpendicular recording, first shipped in 2005,^[11] and as of 2007 the technology was used in many HDDs.^[12]^[13]^[14]

This section may require cleanup to meet Wikipedia's quality standards. Please improve this section if you can. (December 2009)

Grain boundaries are very important to HDD design. The grains are very small and close to each other, so the coupling between adjacent grains is very strong. When one grain is magnetized, the adjacent grains tend to be aligned parallel to it or demagnetized. Then both the stability of the data and signal-to-noise ratio will be sabotaged. A clear grain boundary can weaken the coupling of the grains and subsequently increase the signal-to-noise ratio. In longitudinal recording, the single-domain grains have uniaxial anisotropy with easy axes lying in the film plane. The consequence of this arrangement is that adjacent magnets repel each other. Therefore the magnetostatic energy is so large that it is difficult to increase areal density. Perpendicular recording media, on the other hand, has the easy axis of the grains oriented perpendicular to the disk plane. Adjacent magnets attract to each other and magnetostatic energy are much lower. So, much higher areal density can be achieved in perpendicular recording. Another unique feature in perpendicular recording is that a soft magnetic underlayer are incorporated into the recording disk. This underlayer is used to conduct writing magnetic flux so that the writing is more efficient. This will be discussed in writing process. Therefore, a higher anisotropy medium film, such as L10-FePt and rare-earth magnets, can be used.

[edit] Error handling

Modern drives also make extensive use of Error Correcting Codes (ECCs), particularly Reed–Solomon error correction. These techniques store extra bits for each block of data that are determined by mathematical formulae. The extra bits allow many errors to be fixed. While these extra bits take up space on the hard drive, they allow higher recording densities to be employed, resulting in much larger storage capacity for user data.^[15] In 2009, in the newest drives, low-density parity-check codes (LDPC) are supplanting Reed-Solomon. LDPC codes enable performance close to the Shannon Limit and thus allow for the highest storage density available.^[16]
Typical hard drives attempt to "remap" the data in a physical sector that is going bad to a spare physical sector—hopefully while the number of errors in that bad sector is still small enough that the ECC can completely recover the data without loss. The S.M.A.R.T. system counts the total number of errors in the entire hard drive fixed by ECC, and the total number of remappings, in an attempt to predict hard drive failure.

[edit] Architecture

A hard disk drive with the platters and motor hub removed showing the copper colored stator coils surrounding a bearing at the center of the spindle motor. The orange stripe along the side of the arm is a thin printed-circuit cable. The spindle bearing is in the center.

A typical hard drive has two electric motors, one to spin the disks and one to position the read/write head assembly. The disk motor has an external rotor attached to the platters; the stator windings are fixed in place. The actuator has a read-write head under the tip of its very end (near center); a thin printed-circuit cable connects the read-write head to the hub of the actuator. A flexible, somewhat 'U'-shaped, ribbon cable, seen edge-on below and to the left of the actuator arm in the first image and more clearly in the second, continues the connection from the head to the controller board on the opposite side.
The head support arm is very light, but also rigid; in modern drives, acceleration at the head reaches 550 Gs.
The silver-colored structure at the upper left of the first image is the top plate of the permanent-magnet and moving coil motor that swings the heads to the desired position (it is shown removed in the second image). The plate supports a thin neodymium-iron-boron (NIB) high-flux magnet. Beneath this plate is the moving coil, often referred to as the voice coil by analogy to the coil in loudspeakers, which is attached to the actuator hub, and beneath that is a second NIB magnet, mounted on the bottom plate of the motor (some drives only have one magnet).
The voice coil itself is shaped rather like an arrowhead, and made of doubly coated copper magnet wire. The inner layer is insulation, and the outer is thermoplastic, which bonds the coil together after it's wound on a form, making it self-supporting. The portions of the coil along the two sides of the arrowhead (which point to the actuator bearing center) interact with the magnetic field, developing a tangential force that rotates the actuator. Current flowing radially outward along one side of the arrowhead and radially inward on the other produces the tangential force. If the magnetic field were uniform, each side would generate opposing forces that would cancel each other out. Therefore the surface of the magnet is half N pole, half S pole, with the radial dividing line in the middle, causing the two sides of the coil to see opposite magnetic fields and produce forces that add instead of canceling. Currents along the top and bottom of the coil produce radial forces that do not rotate the head.

[edit] Capacity and access speed

PC hard disk drive capacity (in GB) over time. The vertical axis is logarithmic, so the fit line corresponds to exponential growth.

Using rigid disks and sealing the unit allows much tighter tolerances than in a floppy disk drive. Consequently, hard disk drives can store much more data than floppy disk drives and can access and transmit them faster.

As of May 2010^[update], the highest capacity consumer HDDs are 2 TB.^[17]
A typical "desktop HDD" stores between 120 GB and 3TB (although rarely above 2.5 TB of data based on US market data^[18]), rotates at 5,400 to 15,000 rpm, and has a media transfer rate of 0.5 Gbit/s or higher. (1 GB = 10⁹ Byte; 1 Gbit/s = 10⁹ bit/s)
The fastest “enterprise” HDDs spin at 10,000 or 15,000 rpm, and can achieve sequential media transfer speeds above 1.6 Gbit/s.^[19] and a sustained transfer rate up to 1 Gbit/s.^[19] Drives running at 10,000 or 15,000 rpm use smaller platters to mitigate increased power requirements (as they have less air drag) and therefore generally have lower capacity than the highest capacity desktop drives.
"Mobile HDDs", i.e., laptop HDDs, which are physically smaller than their desktop and enterprise counterparts, tend to be slower and have lower capacity. A typical mobile HDD spins at either 4200 rpm, 5400 rpm, or 7200 rpm, with 5400 rpm being the most prominent. 7200 rpm drives tend to be more expensive and have smaller capacities, while 4200 rpm models usually have very high storage capacities. Because of physically smaller platter(s), mobile HDDs generally have lower capacity than their larger desktop counterparts.

The exponential increases in disk space and data access speeds of HDDs have enabled the commercial viability of consumer products that require large storage capacities, such as digital video recorders and digital audio players.^[20] In addition, the availability of vast amounts of cheap storage has made viable a variety of web-based services with extraordinary capacity requirements, such as free-of-charge web search, web archiving and video sharing (Google, Internet Archive, YouTube, etc.).
The main way to decrease access time is to increase rotational speed, thus reducing rotational delay, while the main way to increase throughput and storage capacity is to increase areal density. Based on historic trends, analysts predict a future growth in HDD bit density (and therefore capacity) of about 40% per year.^[21] Access times have not kept up with throughput increases, which themselves have not kept up with growth in storage capacity.
The expected random IOPS capability of any HDD can be calculated by dividing 1000 msecs by the sum of the average seek time and the average rotational latency.
The first 3.5″ HDD marketed as able to store 1 TB was the Hitachi Deskstar 7K1000. It contains five platters at approximately 200 GB each, providing 1 TB (935.5 GB) of usable space;^[22] note the difference between its capacity in decimal units (1 TB = 10¹² bytes) and binary units where 1 TB = 1024 GB = 2⁴⁰ bytes. Hitachi has since been joined by Samsung (Samsung SpinPoint F1, which has 3 × 334 GB platters), Seagate and Western Digital in the 1 TB drive market.^[23]^[24]
In September 2009, Showa Denko announced capacity improvements in platters that they manufacture for HDD makers. A single 2.5" platter is able to hold 334 GB worth of data, and preliminary results for 3.5" indicate a 750 GB per platter capacity.^[25]

[edit] Capacity measurements

A disassembled and labeled 1997 hard drive. All major components were placed on a mirror, which created the symmetrical reflections.

Raw unformatted capacity of a hard disk drive is usually quoted with SI prefixes (metric system prefixes), incrementing by powers of 1000; today that usually means gigabytes (GB) and terabytes (TB). This is conventional for data speeds and memory sizes which are not inherently manufactured in power of two sizes, as RAM and Flash memory are. Hard disks by contrast have no inherent binary size as capacity is determined by number of heads, tracks and sectors.
This can cause some confusion because some operating systems may report the formatted capacity of a hard drive using binary prefix units which increment by powers of 1024.
A one terabyte (1 TB) disk drive would be expected to hold around 1 trillion bytes (1,000,000,000,000) or 1000 GB; and indeed most 1 TB hard drives will contain slightly more than this number. However some operating system utilities would report this as around 931 GB or 953,674 MB. (The actual number for a formatted capacity will be somewhat smaller still, depending on the file system). Following are the several ways of reporting one Terabyte.

SI prefixes (hard drive)	equivalent	Binary prefixes (OS)	equivalent
1 TB (Terabyte)	1 * 1000⁴ B	0.9095 TB (Terabyte)	0.9095 * 1024⁴ B
1000 GB (Gigabyte)	1000 * 1000³ B	931.3 GB (Gigabyte)	931.3 * 1024³ B
1,000,000 MB (Megabyte)	1,000,000 * 1000² B	953,674.3 MB (Megabyte)	953,674.3 * 1024² B
1,000,000,000 KB (Kilobyte)	1,000,000,000 * 1000 B	976,562,500 KB (Kilobyte)	976,562,500 * 1024 B
1,000,000,000,000 B (byte)	-	1,000,000,000,000 B (byte)	-

Microsoft Windows reports disk capacity both in a decimal integer to 12 or more digits and in binary prefix units to three significant digits.
The capacity of an HDD can be calculated by multiplying the number of cylinders by the number of heads by the number of sectors by the number of bytes/sector (most commonly 512). Drives with the ATA interface and a capacity of eight gigabytes or more behave as if they were structured into 16383 cylinders, 16 heads, and 63 sectors, for compatibility with older operating systems. Unlike in the 1980s, the cylinder, head, sector (C/H/S) counts reported to the CPU by a modern ATA drive are no longer actual physical parameters since the reported numbers are constrained by historic operating-system interfaces and with zone bit recording the actual number of sectors varies by zone. Disks with SCSI interface address each sector with a unique integer number; the operating system remains ignorant of their head or cylinder count.
The old C/H/S scheme has been replaced by logical block addressing. In some cases, to try to "force-fit" the C/H/S scheme to large-capacity drives, the number of heads was given as 64, although no modern drive has anywhere near 32 platters.
For a formatted drive, the operating system's file system internal usage is another, although minor, reason why a computer hard drive or storage device's capacity may show its capacity as different from its theoretical capacity. This would include storage for, as examples, a file allocation table (FAT) or inodes, as well as other operating system data structures. This file system overhead is usually less than 1% on drives larger than 100 MB. For RAID drives, data integrity and fault-tolerance requirements also reduce the realized capacity. For example, a RAID1 drive will be about half the total capacity as a result of data mirroring. For RAID5 drives with x drives you would lose 1/x of your space to parity. RAID drives are multiple drives that appear to be one drive to the user, but provides some fault-tolerance.
A general rule of thumb to quickly convert the manufacturer's hard disk capacity to the standard Microsoft Windows formatted capacity is 0.93*capacity of HDD from manufacturer for HDDs less than a terabyte and 0.91*capacity of HDD from manufacturer for HDDs equal to or greater than 1 terabyte.

[edit] Form factors

5¼″ full height 110 MB HDD,
2½″ (8.5 mm) 6495 MB HDD,
US/UK pennies for comparison.

Six hard drives with 8″, 5.25″, 3.5″, 2.5″, 1.8″, and 1″ disks, partially disassembled to show platters and read-write heads, with a ruler showing inches.

Before the era of PCs and small computers, hard disks were of widely varying dimensions, typically in free standing cabinets the size of washing machines (e.g. DEC RP06 Disk Drive) or designed so that dimensions enabled placement in a 19" rack (e.g. Diablo Model 31).
With increasing sales of small computers having built in floppy-disk drives (FDDs), HDDs that would fit to the FDD mountings became desirable, and this led to the evolution of the market towards drives with certain Form factors, initially derived from the sizes of 8", 5.25" and 3.5" floppy disk drives. Smaller sizes than 3.5" have emerged as popular in the marketplace and/or been decided by various industry groups.

8 in: 9.5 in × 4.624 in × 14.25 in (241.3 mm × 117.5 mm × 362 mm)
In 1979, Shugart Associates' SA1000 was the first form factor compatible HDD, having the same dimensions and a compatible interface to the 8″ FDD.
5.25 inch: 5.75 in × 1.63 in × 8 in (146.1 mm × 41.4 mm × 203 mm)
This smaller form factor, first used in an HDD by Seagate in 1980, was the same size as full height 5¼-inch diameter FDD, i.e., 3.25 inches high. This is twice as high as "half height" commonly used today; i.e., 1.63 in (41.4 mm). Most desktop models of drives for optical 120 mm disks (DVD, CD) use the half height 5¼″ dimension, but it fell out of fashion for HDDs. The Quantum Bigfoot HDD was the last to use it in the late 1990s, with “low-profile” (≈25 mm) and “ultra-low-profile” (≈20 mm) high versions.
3.5 inch: 4 in × 1 in × 5.75 in (101.6 mm × 25.4 mm × 146 mm) = 376.77344 cm³
This smaller form factor, first used in an HDD by Rodime in 1984, was the same size as the "half height" 3½″ FDD, i.e., 1.63 inches high. Today it has been largely superseded by 1-inch high “slimline” or “low-profile” versions of this form factor which is used by most desktop HDDs.
2.5 inch: 2.75 in × 0.374–0.59 in × 3.945 in (69.85 mm × 7–15 mm × 100 mm) = 48.895–104.775 cm³
This smaller form factor was introduced by PrairieTek in 1988; there is no corresponding FDD. It is widely used today for hard-disk drives in mobile devices (laptops, music players, etc.) and as of 2008 replacing 3.5 inch enterprise-class drives. It is also used in the Xbox 360 and Playstation 3 video game consoles. Today, the dominant height of this form factor is 9.5 mm for laptop drives, but high capacity drives (750 GB and 1 TB) have a height of 12.5 mm. Enterprise-class drives can have a height up to 15 mm.^[26] Seagate has released a wafer-thin 7mm drive aimed at entry level laptops and high end netbooks in December 2009.^[27]
1.8 inch: 54 mm × 8 mm × 71 mm = 30.672 cm³
This form factor, originally introduced by Integral Peripherals in 1993, has evolved into the ATA-7 LIF with dimensions as stated. It is increasingly used in digital audio players and subnotebooks. An original variant exists for 2–5 GB sized HDDs that fit directly into a PC card expansion slot. These became popular for their use in iPods and other HDD based MP3 players.
1 inch: 42.8 mm × 5 mm × 36.4 mm
This form factor was introduced in 1999 as IBM's Microdrive to fit inside a CF Type II slot. Samsung calls the same form factor "1.3 inch" drive in its product literature.^[28]
0.85 inch: 24 mm × 5 mm × 32 mm
Toshiba announced this form factor in January 2004^[29] for use in mobile phones and similar applications, including SD/MMC slot compatible HDDs optimized for video storage on 4G handsets. Toshiba currently sells a 4 GB (MK4001MTD) and 8 GB (MK8003MTD) version [2] and holds the Guinness World Record for the smallest hard disk drive.^[30]

3.5" and 2.5" hard disks currently dominate the market.
By 2009 all manufacturers had discontinued the development of new products for the 1.3-inch, 1-inch and 0.85-inch form factors due to falling prices of flash memory.^[31]^[32]
The inch-based nickname of all these form factors usually do not indicate any actual product dimension (which are specified in millimeters for more recent form factors), but just roughly indicate a size relative to disk diameters, in the interest of historic continuity.

[edit] Current hard disk form factors

Form factor	Width	Height	Largest capacity	Platters (Max)
3.5″	102 mm	25.4 mm	2 TB^[33] (2009)	5
2.5″	69.9 mm	7-15 mm	1 TB^[34] (2009)	3
1.8″	54 mm	8 mm	320 GB^[35] (2009)	3

[edit] Obsolete hard disk form factors

Form factor	Width	Largest capacity	Platters (Max)
5.25″ FH	146 mm	47 GB^[36] (1998)	14
5.25″ HH	146 mm	19.3 GB^[37] (1998)	4^[38]
1.3″	43 mm	40 GB^[39] (2007)	1
1″ (CFII/ZIF/IDE-Flex)	42 mm	20 GB (2006)	1
0.85″	24 mm	8 GB^[40] (2004)	1

[edit] Other characteristics

[edit] Data transfer rate

As of 2008, a typical 7200 rpm desktop hard drive has a sustained "disk-to-buffer" data transfer rate of about 70 megabytes per second.^[41] This rate depends on the track location, so it will be higher for data on the outer tracks (where there are more data sectors) and lower toward the inner tracks (where there are fewer data sectors); and is generally somewhat higher for 10,000 rpm drives. A current widely used standard for the "buffer-to-computer" interface is 3.0 Gbit/s SATA, which can send about 300 megabyte/s from the buffer to the computer, and thus is still comfortably ahead of today's disk-to-buffer transfer rates. Data transfer rate (read/write) can be measured by writing a large file to disk using special file generator tools, then reading back the file. Transfer rate can be influenced by file system fragmentation and the layout of the files.

[edit] Seek time

Seek time ranges from just under 2 ms for high-end server drives, to 15 ms for miniature drives, with the most common desktop type typically being around 9 ms.^{[citation needed]} There has not been any significant improvement in this speed for some years. Some early PC drives used a stepper motor to move the heads, and as a result had access times as slow as 80–120 ms, but this was quickly improved by voice coil type actuation in the late 1980s, reducing access times to around 20 ms.

[edit] Power consumption

Power consumption has become increasingly important, not just in mobile devices such as laptops but also in server and desktop markets. Increasing data center machine density has led to problems delivering sufficient power to devices (especially for spin up), and getting rid of the waste heat subsequently produced, as well as environmental and electrical cost concerns (see green computing). Similar issues exist for large companies with thousands of desktop PCs. Smaller form factor drives often use less power than larger drives. One interesting development in this area is actively controlling the seek speed so that the head arrives at its destination only just in time to read the sector, rather than arriving as quickly as possible and then having to wait for the sector to come around (i.e. the rotational latency). Many of the hard drive companies are now producing Green Drives that require much less power and cooling. Many of these 'Green Drives' spin slower (<5,400 rpm compared to 7,200, 10,000 or 15,000 rpm) and also generate less waste heat.
Also in Server and Workstation systems where there might be multiple hard disk drives, there are various ways of controlling when the hard drives spin up (highest power draw).
On SCSI hard disk drives, the SCSI controller can directly control spin up and spin down of the drives.
On Parallel ATA (aka PATA) and SATA hard disk drives, some support Power-up in standby or PUIS. The hard disk drive will not spin up until the controller or system BIOS issues a specific command to do so. This limits the power draw or consumption upon power on.
On newer SATA hard disk drives, there is Staggered Spin Up feature. The hard disk drive will not spin up until the SATA Phy comes ready (communications with the host controller starts).^{[citation needed]}
To further control or reduce power draw and consumption, the hard disk drive can be spun down to reduce its power consumption.

[edit] Audible noise

Measured in dBA, audible noise is significant for certain applications, such as PVRs, digital audio recording and quiet computers. Low noise disks typically use fluid bearings, slower rotational speeds (usually 5,400 rpm) and reduce the seek speed under load (AAM) to reduce audible clicks and crunching sounds. Drives in smaller form factors (e.g. 2.5 inch) are often quieter than larger drives.

[edit] Shock resistance

Shock resistance is especially important for mobile devices. Some laptops now include active hard drive protection that parks the disk heads if the machine is dropped, hopefully before impact, to offer the greatest possible chance of survival in such an event. Maximum shock tolerance to date is 350 Gs for operating and 1000 Gs for non-operating.^[42]

[edit] Access and interfaces

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Hard disk drives are accessed over one of a number of bus types, including parallel ATA (P-ATA, also called IDE or EIDE), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel. Bridge circuitry is sometimes used to connect hard disk drives to buses that they cannot communicate with natively, such as IEEE 1394, USB and SCSI.
For the ST-506 interface, the data encoding scheme as written to the disk surface was also important. The first ST-506 disks used Modified Frequency Modulation (MFM) encoding, and transferred data at a rate of 5 megabits per second. Later controllers using 2,7 RLL (or just "RLL") encoding caused 50% more data to appear under the heads compared to one rotation of an MFM drive, increasing data storage and data transfer rate by 50%, to 7.5 megabits per second.
Many ST-506 interface disk drives were only specified by the manufacturer to run at the 1/3rd lower MFM data transfer rate compared to RLL, while other drive models (usually more expensive versions of the same drive) were specified to run at the higher RLL data transfer rate. In some cases, a drive had sufficient margin to allow the MFM specified model to run at the denser/faster RLL data transfer rate (not recommended nor guaranteed by manufacturers). Also, any RLL-certified drive could run on any MFM controller, but with 1/3 less data capacity and as much as 1/3rd less data transfer rate compared to its RLL specifications.
Enhanced Small Disk Interface (ESDI) also supported multiple data rates (ESDI disks always used 2,7 RLL, but at 10, 15 or 20 megabits per second), but this was usually negotiated automatically by the disk drive and controller; most of the time, however, 15 or 20 megabit ESDI disk drives weren't downward compatible (i.e. a 15 or 20 megabit disk drive wouldn't run on a 10 megabit controller). ESDI disk drives typically also had jumpers to set the number of sectors per track and (in some cases) sector size.
Modern hard drives present a consistent interface to the rest of the computer, no matter what data encoding scheme is used internally. Typically a DSP in the electronics inside the hard drive takes the raw analog voltages from the read head and uses PRML and Reed–Solomon error correction^[43] to decode the sector boundaries and sector data, then sends that data out the standard interface. That DSP also watches the error rate detected by error detection and correction, and performs bad sector remapping, data collection for Self-Monitoring, Analysis, and Reporting Technology, and other internal tasks.
SCSI originally had just one signaling frequency of 5 MHz for a maximum data rate of 5 megabytes/second over 8 parallel conductors, but later this was increased dramatically. The SCSI bus speed had no bearing on the disk's internal speed because of buffering between the SCSI bus and the disk drive's internal data bus; however, many early disk drives had very small buffers, and thus had to be reformatted to a different interleave (just like ST-506 disks) when used on slow computers, such as early Commodore Amiga, IBM PC compatibles and Apple Macintoshes.
ATA disks have typically had no problems with interleave or data rate, due to their controller design, but many early models were incompatible with each other and couldn't run with two devices on the same physical cable in a master/slave setup. This was mostly remedied by the mid-1990s, when ATA's specification was standardized and the details began to be cleaned up, but still causes problems occasionally (especially with CD-ROM and DVD-ROM disks, and when mixing Ultra DMA and non-UDMA devices).
Serial ATA does away with master/slave setups entirely, placing each disk on its own channel (with its own set of I/O ports) instead.
FireWire/IEEE 1394 and USB(1.0/2.0) HDDs are external units containing generally ATA or SCSI disks with ports on the back allowing very simple and effective expansion and mobility. Most FireWire/IEEE 1394 models are able to daisy-chain in order to continue adding peripherals without requiring additional ports on the computer itself. USB however, is a point to point network and doesn't allow for daisy-chaining. USB hubs are used to increase the number of available ports and are used for devices that don't require charging since the current supplied by hubs is typically lower than what's available from the built-in USB ports.

[edit] Disk interface families used in personal computers

Notable families of disk interfaces include:

Historical bit serial interfaces — connect a hard disk drive (HDD) to a hard disk controller (HDC) with two cables, one for control and one for data. (Each drive also has an additional cable for power, usually connecting it directly to the power supply unit). The HDC provided significant functions such as serial/parallel conversion, data separation, and track formatting, and required matching to the drive (after formatting) in order to assure reliability. Each control cable could serve two or more drives, while a dedicated (and smaller) data cable served each drive.
- ST506 used MFM (Modified Frequency Modulation) for the data encoding method.
- ST412 was available in either MFM or RLL (Run Length Limited) encoding variants.
- Enhanced Small Disk Interface (ESDI) was an interface developed by Maxtor to allow faster communication between the processor and the disk than MFM or RLL.

Modern bit serial interfaces — connect a hard disk drive to a host bus interface adapter (today typically integrated into the "south bridge") with one data/control cable. (As for historical bit serial interfaces above, each drive also has an additional power cable, usually direct to the power supply unit.)
- Fibre Channel (FC), is a successor to parallel SCSI interface on enterprise market. It is a serial protocol. In disk drives usually the Fibre Channel Arbitrated Loop (FC-AL) connection topology is used. FC has much broader usage than mere disk interfaces, and it is the cornerstone of storage area networks (SANs). Recently other protocols for this field, like iSCSI and ATA over Ethernet have been developed as well. Confusingly, drives usually use copper twisted-pair cables for Fibre Channel, not fibre optics. The latter are traditionally reserved for larger devices, such as servers or disk array controllers.
- Serial ATA (SATA). The SATA data cable has one data pair for differential transmission of data to the device, and one pair for differential receiving from the device, just like EIA-422. That requires that data be transmitted serially. Similar differential signaling system is used in RS485, LocalTalk, USB, Firewire, and differential SCSI.
- Serial Attached SCSI (SAS). The SAS is a new generation serial communication protocol for devices designed to allow for much higher speed data transfers and is compatible with SATA. SAS uses a mechanically identical data and power connector to standard 3.5" SATA1/SATA2 HDDs, and many server-oriented SAS RAID controllers are also capable of addressing SATA hard drives. SAS uses serial communication instead of the parallel method found in traditional SCSI devices but still uses SCSI commands.

Word serial interfaces — connect a hard disk drive to a host bus adapter (today typically integrated into the "south bridge") with one cable for combined data/control. (As for all bit serial interfaces above, each drive also has an additional power cable, usually direct to the power supply unit.) The earliest versions of these interfaces typically had a 8 bit parallel data transfer to/from the drive, but 16 bit versions became much more common, and there are 32 bit versions. Modern variants have serial data transfer. The word nature of data transfer makes the design of a host bus adapter significantly simpler than that of the precursor HDD controller.
- Integrated Drive Electronics (IDE), later renamed to ATA, with the alias P-ATA ("parallel ATA") retroactively added upon introduction of the new variant Serial ATA. The original name reflected the innovative integration of HDD controller with HDD itself, which was not found in earlier disks. Moving the HDD controller from the interface card to the disk drive helped to standardize interfaces, and to reduce the cost and complexity. The 40 pin IDE/ATA connection transfers 16 bits of data at a time on the data cable. The data cable was originally 40 conductor, but later higher speed requirements for data transfer to and from the hard drive led to an "ultra DMA" mode, known as UDMA. Progressively faster versions of this standard ultimately added the requirement for an 80 conductor variant of the same cable; where half of the conductors provides grounding necessary for enhanced high-speed signal quality by reducing cross talk. The interface for 80 conductor only has 39 pins, the missing pin acting as a key to prevent incorrect insertion of the connector to an incompatible socket, a common cause of disk and controller damage.
- EIDE was an unofficial update (by Western Digital) to the original IDE standard, with the key improvement being the use of direct memory access (DMA) to transfer data between the disk and the computer without the involvement of the CPU, an improvement later adopted by the official ATA standards. By directly transferring data between memory and disk, DMA eliminates the need for the CPU to copy byte per byte, therefore allowing it to process other tasks while the data transfer occurs.
- Small Computer System Interface (SCSI), originally named SASI for Shugart Associates System Interface, was an early competitor of ESDI. SCSI disks were standard on servers, workstations, Commodore Amiga and Apple Macintosh computers through the mid-90s, by which time most models had been transitioned to IDE (and later, SATA) family disks. Only in 2005 did the capacity of SCSI disks fall behind IDE disk technology, though the highest-performance disks are still available in SCSI and Fibre Channel only. The length limitations of the data cable allows for external SCSI devices. Originally SCSI data cables used single ended (common mode) data transmission, but server class SCSI could use differential transmission, either low voltage differential (LVD) or high voltage differential (HVD). ("Low" and "High" voltages for differential SCSI are relative to SCSI standards and do not meet the meaning of low voltage and high voltage as used in general electrical engineering contexts, as apply e.g. to statutory electrical codes; both LVD and HVD use low voltage signals (3.3 V and 5 V respectively) in general terminology.)

Acronym or abbreviation	Meaning	Description
SASI	Shugart Associates System Interface	Historical predecessor to SCSI.
SCSI	Small Computer System Interface	Bus oriented that handles concurrent operations.
SAS	Serial Attached SCSI	Improvement of SCSI, uses serial communication instead of parallel.
ST-506	Seagate Technology	Historical Seagate interface.
ST-412	Seagate Technology	Historical Seagate interface (minor improvement over ST-506).
ESDI	Enhanced Small Disk Interface	Historical; backwards compatible with ST-412/506, but faster and more integrated.
ATA	Advanced Technology Attachment	Successor to ST-412/506/ESDI by integrating the disk controller completely onto the device. Incapable of concurrent operations.
SATA	Serial ATA	Modification of ATA, uses serial communication instead of parallel.

[edit] Integrity

An IBM HDD head resting on a disk platter. Since the drive is not in operation, the head is simply pressed against the disk by the suspension.

Close-up of a hard disk head resting on a disk platter. A reflection of the head and its suspension is visible on the mirror-like disk.

Due to the extremely close spacing between the heads and the disk surface, any contamination of the read-write heads or platters can lead to a head crash — a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film and causing data loss. Head crashes can be caused by electronic failure, a sudden power failure, physical shock, wear and tear, corrosion, or poorly manufactured platters and heads.
The HDD's spindle system relies on air pressure inside the disk enclosure to support the heads at their proper flying height while the disk rotates. Hard disk drives require a certain range of air pressures in order to operate properly. The connection to the external environment and pressure occurs through a small hole in the enclosure (about 0.5 mm in diameter), usually with a filter on the inside (the breather filter).^[44] If the air pressure is too low, then there is not enough lift for the flying head, so the head gets too close to the disk, and there is a risk of head crashes and data loss. Specially manufactured sealed and pressurized disks are needed for reliable high-altitude operation, above about 3,000 m (10,000 feet).^[45] Modern disks include temperature sensors and adjust their operation to the operating environment. Breather holes can be seen on all disk drives — they usually have a sticker next to them, warning the user not to cover the holes. The air inside the operating drive is constantly moving too, being swept in motion by friction with the spinning platters. This air passes through an internal recirculation (or "recirc") filter to remove any leftover contaminants from manufacture, any particles or chemicals that may have somehow entered the enclosure, and any particles or outgassing generated internally in normal operation. Very high humidity for extended periods can corrode the heads and platters.
For giant magnetoresistive (GMR) heads in particular, a minor head crash from contamination (that does not remove the magnetic surface of the disk) still results in the head temporarily overheating, due to friction with the disk surface, and can render the data unreadable for a short period until the head temperature stabilizes (so called "thermal asperity", a problem which can partially be dealt with by proper electronic filtering of the read signal).

[edit] Actuation of moving arm

The hard drive's electronics control the movement of the actuator and the rotation of the disk, and perform reads and writes on demand from the disk controller. Feedback of the drive electronics is accomplished by means of special segments of the disk dedicated to servo feedback. These are either complete concentric circles (in the case of dedicated servo technology), or segments interspersed with real data (in the case of embedded servo technology). The servo feedback optimizes the signal to noise ratio of the GMR sensors by adjusting the voice-coil of the actuated arm. The spinning of the disk also uses a servo motor. Modern disk firmware is capable of scheduling reads and writes efficiently on the platter surfaces and remapping sectors of the media which have failed.

[edit] Landing zones and load/unload technology

A read/write head from a circa-1998 Fujitsu 3.5" hard disk. The area pictured is approximately 2.0 mm x 3.0mm.

Microphotograph of an older generation hard disk head and slider (1990s). The size of the front face (which is the "trailing face" of the slider) is about 0.3 mm × 1.0 mm. It is the location of the actual 'head' (magnetic sensors). The non-visible bottom face of the slider is about 1.0 mm × 1.25 mm (so-called "nano" size) and faces the platter. It contains the lithographically micro-machined air bearing surface (ABS) that allows the slider to fly in a highly controlled fashion. One functional part of the head is the round, orange structure visible in the middle - the lithographically defined copper coil of the write transducer. Also note the electric connections by wires bonded to gold-plated pads.

Modern HDDs prevent power interruptions or other malfunctions from landing its heads in the data zone by parking the heads either in a landing zone or by unloading (i.e., load/unload) the heads. Some early PC HDDs did not park the heads automatically and they would land on data. In some other early units the user manually parked the heads by running a program to park the HDD's heads.
A landing zone is an area of the platter usually near its inner diameter (ID), where no data are stored. This area is called the Contact Start/Stop (CSS) zone. Disks are designed such that either a spring or, more recently, rotational inertia in the platters is used to park the heads in the case of unexpected power loss. In this case, the spindle motor temporarily acts as a generator, providing power to the actuator.
Spring tension from the head mounting constantly pushes the heads towards the platter. While the disk is spinning, the heads are supported by an air bearing and experience no physical contact or wear. In CSS drives the sliders carrying the head sensors (often also just called heads) are designed to survive a number of landings and takeoffs from the media surface, though wear and tear on these microscopic components eventually takes its toll. Most manufacturers design the sliders to survive 50,000 contact cycles before the chance of damage on startup rises above 50%. However, the decay rate is not linear: when a disk is younger and has had fewer start-stop cycles, it has a better chance of surviving the next startup than an older, higher-mileage disk (as the head literally drags along the disk's surface until the air bearing is established). For example, the Seagate Barracuda 7200.10 series of desktop hard disks are rated to 50,000 start-stop cycles, in other words no failures attributed to the head-platter interface were seen before at least 50,000 start-stop cycles during testing.^[46]
Around 1995 IBM pioneered a technology where a landing zone on the disk is made by a precision laser process (Laser Zone Texture = LZT) producing an array of smooth nanometer-scale "bumps" in a landing zone,^[47] thus vastly improving stiction and wear performance. This technology is still largely in use today (2008), predominantly in desktop and enterprise (3.5 inch) drives. In general, CSS technology can be prone to increased stiction (the tendency for the heads to stick to the platter surface), e.g. as a consequence of increased humidity. Excessive stiction can cause physical damage to the platter and slider or spindle motor.
Load/Unload technology relies on the heads being lifted off the platters into a safe location, thus eliminating the risks of wear and stiction altogether. The first HDD RAMAC and most early disk drives used complex mechanisms to load and unload the heads. Modern HDDs use ramp loading, first introduced by Memorex in 1967,^[48] to load/unload onto plastic "ramps" near the outer disk edge.
All HDDs today still use one of these two technologies listed above. Each has a list of advantages and drawbacks in terms of loss of storage area on the disk, relative difficulty of mechanical tolerance control, non-operating shock robustness, cost of implementation, etc.
Addressing shock robustness, IBM also created a technology for their ThinkPad line of laptop computers called the Active Protection System. When a sudden, sharp movement is detected by the built-in accelerometer in the Thinkpad, internal hard disk heads automatically unload themselves to reduce the risk of any potential data loss or scratch defects. Apple later also utilized this technology in their PowerBook, iBook, MacBook Pro, and MacBook line, known as the Sudden Motion Sensor. Sony,^[49] HP with their HP 3D DriveGuard^[50] and Toshiba^[51] have released similar technology in their notebook computers.
This accelerometer based shock sensor has also been used for building cheap earthquake sensor networks.^[52]

[edit] Disk failures and their metrics

Wikibooks has a book on the topic of

Minimizing hard disk drive failure and data loss

Most major hard disk and motherboard vendors now support S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology), which measures drive characteristics such as operating temperature, spin-up time, data error rates, etc. Certain trends and sudden changes in these parameters are thought to be associated with increased likelihood of drive failure and data loss.
However, not all failures are predictable. Normal use eventually can lead to a breakdown in the inherently fragile device, which makes it essential for the user to periodically back up the data onto a separate storage device. Failure to do so can lead to the loss of data. While it may sometimes be possible to recover lost information, it is normally an extremely costly procedure, and it is not possible to guarantee success. A 2007 study published by Google suggested very little correlation between failure rates and either high temperature or activity level; however, the correlation between manufacturer/model and failure rate was relatively strong. Statistics in this matter is kept highly secret by most entities. Google did not publish the manufacturer's names along with their respective failure rates,^[53] though they have since revealed that they use Hitachi Deskstar drives in some of their servers.^[54] While several S.M.A.R.T. parameters have an impact on failure probability, a large fraction of failed drives do not produce predictive S.M.A.R.T. parameters.^[53] S.M.A.R.T. parameters alone may not be useful for predicting individual drive failures.^[53]
A common misconception is that a colder hard drive will last longer than a hotter hard drive. The Google study seems to imply the reverse—"lower temperatures are associated with higher failure rates". Hard drives with S.M.A.R.T.-reported average temperatures below 27 °C (80.6 °F) had higher failure rates than hard drives with the highest reported average temperature of 50 °C (122 °F), failure rates at least twice as high as the optimum S.M.A.R.T.-reported temperature range of 36 °C (96.8 °F) to 47 °C (116.6 °F).^[53]
SCSI, SAS and FC drives are typically more expensive and are traditionally used in servers and disk arrays, whereas inexpensive ATA and SATA drives evolved in the home computer market and were perceived to be less reliable. This distinction is now becoming blurred.
The mean time between failures (MTBF) of SATA drives is usually about 600,000 hours (some drives such as Western Digital Raptor have rated 1.4 million hours MTBF)^[55], while SCSI drives are rated for upwards of 1.5 million hours.^{[citation needed]} However, independent research indicates that MTBF is not a reliable estimate of a drive's longevity.^[56] MTBF is conducted in laboratory environments in test chambers and is an important metric to determine the quality of a disk drive before it enters high volume production. Once the drive product is in production, the more valid metric is annualized failure rate (AFR).^{[citation needed]} AFR is the percentage of real-world drive failures after shipping.
SAS drives are comparable to SCSI drives, with high MTBF and high reliability.^{[citation needed]}
Enterprise S-ATA drives designed and produced for enterprise markets, unlike standard S-ATA drives, have reliability comparable to other enterprise class drives.^[57]^[58]
Typically enterprise drives (all enterprise drives, including SCSI, SAS, enterprise SATA and FC) experience between 0.70%-0.78% annual failure rates from the total installed drives.^{[citation needed]}
Eventually all mechanical hard disk drives fail, so to mitigate loss of data, some form of redundancy is needed, such as RAID^[59] or a regular backup^[59] system.

[edit] Manufacturers

A Western Digital 3.5 inch 250 GB SATA HDD. This specific model features both SATA and Molex power inputs.

Seagate's hard disk drives being manufactured in a factory in Wuxi, China

See also List of defunct hard disk manufacturers

The technological resources and know-how required for modern drive development and production mean that as of 2010, virtually all of the world's HDDs are manufactured by just five large companies: Seagate, Western Digital, Hitachi, Samsung, and Toshiba.
Dozens of former HDD manufacturers have gone out of business, merged, or closed their HDD divisions; as capacities and demand for products increased, profits became hard to find, and the market underwent significant consolidation in the late 1980s and late 1990s. The first notable casualty of the business in the PC era was Computer Memories Inc. or CMI; after an incident with faulty 20 MB AT disks in 1985,^[60] CMI's reputation never recovered, and they exited the HDD business in 1987. Another notable failure was MiniScribe, who went bankrupt in 1990 after it was found that they had engaged in accounting fraud and inflated sales numbers for several years. Many other smaller companies (like Kalok, Microscience, LaPine, Areal, Priam and PrairieTek) also did not survive the shakeout, and had disappeared by 1993; Micropolis was able to hold on until 1997, and JTS, a relative latecomer to the scene, lasted only a few years and was gone by 1999, after attempting to manufacture HDDs in India. Their claim to fame was creating a new 3″ form factor drive for use in laptops. Quantum and Integral also invested in the 3″ form factor; but eventually ceased support as this form factor failed to catch on. Rodime was also an important manufacturer during the 1980s, but stopped making disks in the early 1990s amid the shakeout and now concentrates on technology licensing; they hold a number of patents related to 3.5-inch form factor HDDs.
The following is the genealogy of the current HDD companies:

1967: Hitachi enters the HDD business.
1967: Toshiba enters the HDD business.
1979: Seagate Technology^[61] founded.
1988: Western Digital, then a well-known controller designer, enters the HDD business by acquiring Tandon Corporation's disk manufacturing division.^[62]
1989: Seagate Technology purchases Control Data's HDD business.
1990: Maxtor purchases MiniScribe out of bankruptcy, making it the core of its low-end HDDs.
1994: Quantum purchases DEC's storage division, giving it a high-end disk range to go with its more consumer-oriented ProDrive range.
1996: Seagate acquires Conner Peripherals in a merger.
2000: Maxtor acquires Quantum's HDD business; Quantum remains in the tape business.
2003: Hitachi acquires the majority of IBM's disk division, renaming it Hitachi Global Storage Technologies (HGST).
2006: Seagate acquires Maxtor.
2009: Toshiba acquires Fujitsu's HDD division.^[63]

[edit] Sales

In the year 2007 516.2 million hard disks were sold.^[64]

[edit] Icons

Hard drives are traditionally symbolized as either a stylized stack of platters (in orthographic projection) or, more abstractly, as a cylinder. This is particularly found in schematic diagrams or on indicator lights, as on laptops, to indicate hard drive access. In most modern operating systems, hard drives are instead represented by an illustration or photograph of a hard drive enclosure. These are illustrated below.

Today, hard drives are symbolized by a picture of the enclosure.

Schematically, hard drives may be represented by cylinders or stacks of platters, as in this RAID diagram.

The cylinder schematic derives from hard drives internally being a stack of platters, as in these 1970s vintage hard drive internals.

[edit] See also

Automatic Acoustic Management
Binary prefix
Clean Room
Click of death
Data erasure
Disk formatting
Drive mapping
du (Unix disk usage program)
External hard disk drive
File System
HDD recorder
History of hard disk drives
Hybrid drive
IBM 305 RAMAC
kilobyte, megabyte, gigabyte definitions
Multimedia
Solid-state drive
Spintronics
Write precompensation
http://en.wikipedia.org/wiki/Hard_disk_drive
06/01/10

What is an Intranet

2010-06-01T13:39:00.002-04:00

An intranet is a private computer network that uses Internet Protocol technologies to securely share any part of an organization's information or network operating system within that organization. The term is used in contrast to internet, a network between organizations, and instead refers to a network within an organization. Sometimes the term refers only to the organization's internal website, but may be a more extensive part of the organization's information technology infrastructure. It may host multiple private websites and constitute an important component and focal point of internal communication and collaboration.

[hide]

[edit] Characteristics

An intranet is built from the same concepts and technologies used for the Internet, such as client–server computing and the Internet Protocol Suite (TCP/IP). Any of the well known Internet protocols may be found in an intranet, such as HTTP (web services), SMTP (e-mail), and FTP (file transfer). Internet technologies are often deployed to provide modern interfaces to legacy information systems hosting corporate data.
An intranet can be understood as a private analog of the Internet, or as a private extension of the Internet confined to an organization. The first intranet websites and home pages began to appear in organizations in 1990-1991. Although not officially noted, the term intranet first became common-place among early adopters, such as universities and technology corporations, in 1992.^{[dubious – discuss]}
Intranets are also contrasted with extranets. While intranets are generally restricted to employees of the organization, extranets may also be accessed by customers, suppliers, or other approved parties.^[1] Extranets extend a private network onto the Internet with special provisions for access, authorization, and authentication (AAA protocol).
Intranets may provide a gateway to the Internet by means of a network gateway with a firewall, shielding the intranet from unauthorized external access. The gateway often also implements user authentication, encryption of messages, and often virtual private network (VPN) connectivity for off-site employees to access company information, computing resources and internal communications.

[edit] Uses

Increasingly, intranets are being used to deliver tools and applications, e.g., collaboration (to facilitate working in groups and teleconferencing) or sophisticated corporate directories, sales and customer relationship management tools, project management etc., to advance productivity.
Intranets are also being used as corporate culture-change platforms. For example, large numbers of employees discussing key issues in an intranet forum application could lead to new ideas in management, productivity, quality, and other corporate issues.
In large intranets, website traffic is often similar to public website traffic and can be better understood by using web metrics software to track overall activity. User surveys also improve intranet website effectiveness. Larger businesses allow users within their intranet to access public internet through firewall servers. They have the ability to screen messages coming and going keeping security intact.
When part of an intranet is made accessible to customers and others outside the business, that part becomes part of an extranet. Businesses can send private messages through the public network, using special encryption/decryption and other security safeguards to connect one part of their intranet to another.
Intranet user-experience, editorial, and technology teams work together to produce in-house sites. Most commonly, intranets are managed by the communications, HR or CIO departments of large organizations, or some combination of these.
Because of the scope and variety of content and the number of system interfaces, intranets of many organizations are much more complex than their respective public websites. Intranets and their use are growing rapidly. According to the Intranet design annual 2007 from Nielsen Norman Group, the number of pages on participants' intranets averaged 200,000 over the years 2001 to 2003 and has grown to an average of 6 million pages over 2005–2007.^[2]

[edit] Benefits

Workforce productivity: Intranets can also help users to locate and view information faster and use applications relevant to their roles and responsibilities. With the help of a web browser interface, users can access data held in any database the organization wants to make available, anytime and - subject to security provisions - from anywhere within the company workstations, increasing employees' ability to perform their jobs faster, more accurately, and with confidence that they have the right information. It also helps to improve the services provided to the users.
Time: Intranets allow organizations to distribute information to employees on an as-needed basis; Employees may link to relevant information at their convenience, rather than being distracted indiscriminately by electronic mail.
Communication: Intranets can serve as powerful tools for communication within an organization, vertically and horizontally. From a communications standpoint, intranets are useful to communicate strategic initiatives that have a global reach throughout the organization. The type of information that can easily be conveyed is the purpose of the initiative and what the initiative is aiming to achieve, who is driving the initiative, results achieved to date, and who to speak to for more information. By providing this information on the intranet, staff have the opportunity to keep up-to-date with the strategic focus of the organization. Some examples of communication would be chat, email, and or blogs. A great real world example of where an intranet helped a company communicate is when Nestle had a number of food processing plants in Scandinavia. Their central support system had to deal with a number of queries every day (McGovern, Gerry). When Nestle decided to invest in an intranet, they quickly realized the savings. McGovern says the savings from the reduction in query calls was substantially greater than the investment in the intranet.
Web publishing allows cumbersome corporate knowledge to be maintained and easily accessed throughout the company using hypermedia and Web technologies. Examples include: employee manuals, benefits documents, company policies, business standards, newsfeeds, and even training, can be accessed using common Internet standards (Acrobat files, Flash files, CGI applications). Because each business unit can update the online copy of a document, the most recent version is always available to employees using the intranet.
Business operations and management: Intranets are also being used as a platform for developing and deploying applications to support business operations and decisions across the internetworked enterprise.
Cost-effective: Users can view information and data via web-browser rather than maintaining physical documents such as procedure manuals, internal phone list and requisition forms. This can potentially save the business money on printing, duplicating documents, and the environment as well as document maintenance overhead. "PeopleSoft, a large software company, has derived significant cost savings by shifting HR processes to the intranet" ^[3]. Gerry McGovern goes on to say the manual cost of enrolling in benefits was found to be USD109.48 per enrollment. "Shifting this process to the intranet reduced the cost per enrollment to $21.79; a saving of 80 percent" ^[3]. PeopleSoft also saved some money when they received requests for mailing address change. "For an individual to request a change to their mailing address, the manual cost was USD17.77. The intranet reduced this cost to USD4.87, a saving of 73 percent" ^[3]. PeopleSoft was just one of the many companies that saved money by using an intranet. Another company that saved a lot of money on expense reports was Cisco. "In 1996, Cisco processed 54,000 reports and the amount of dollars processed was USD19 million" ^[3].
Promote common corporate culture: Every user is viewing the same information within the Intranet.
Enhance Collaboration: With information easily accessible by all authorised users, teamwork is enabled.
Cross-platform Capability: Standards-compliant web browsers are available for Windows, Mac, and UNIX.
Built for One Audience: Many companies dictate computer specifications. Which, in turn, may allow Intranet developers to write applications that only have to work on one browser (no cross-browser compatibility issues).
Knowledge of your Audience: Being able to specifically address your "viewer" is a great advantange. Since Intranets are user specific (requiring database/network authentication prior to access), you know exactly who you are interfacing with. So, you can personalize your Intranet based on role (job title, department) or individual ("Congratulations Jane, on your 3rd year with our company!").
Immediate Updates: When dealing with the public in any capacity, laws/specifications/parameters can change. With an Intranet and providing your audience with "live" changes, they are never out of date, which can limit a company's liability.
Supports a distributed computing architecture: The intranet can also be linked to a company’s management information system, for example a time keeping system.

[edit] Planning and creation

Most organizations devote considerable resources into the planning and implementation of their intranet as it is of strategic importance to the organization's success. Some of the planning would include topics such as:

The purpose and goals of the intranet
Persons or departments responsible for implementation and management
Functional plans, information architecture, page layouts, design.^[4]
Implementation schedules and phase-out of existing systems
Defining and implementing security of the intranet
How to ensure it is within legal boundaries and other constraints
Level of interactivity (eg wikis, on-line forms) desired.
Is the input of new data and updating of existing data to be centrally controlled or devolved.

These are in addition to the hardware and software decisions (like content management systems), participation issues (like good taste, harassment, confidentiality), and features to be supported^[5].

Intranets are often static sites, basically they are essentially a shared drive, serving up centrally stored documents alongside internal articles or communications - often one-way communication. However organisations are now starting to think of how their intranets can become a 'communication hub' for their team by using companies specialising in 'socialising' intranets.^[6]

The actual implementation would include steps such as:

Securing senior management support and funding.^[7]
Business requirements analysis.
User involvement to identify users' information needs.
Installation of web server and user access network.
Installing required user applications on computers.
Creation of document framework for the content to be hosted.^[8]
User involvement in testing and promoting use of intranet.
Ongoing measurement and evaluation, including through benchmarking against other intranets.^[9]

Useful components of an intranet structure might include:

Key personnel committed to maintaining the Intranet and keeping content current.
Social networking is useful as a feedback forum for users to indicate what they want and what they do not like.
http://en.wikipedia.org/wiki/Intranet
06/01/10

Quality IT Computer Tips

Computer Keyboard Shortcuts

Windows system key combinations

Windows program key combinations

Mouse click/keyboard modifier combinations for shell objects

General keyboard-only commands

Shell objects and general folder/Windows Explorer shortcuts

To copy a file

To create a shortcut

General folder/shortcut control

Windows Explorer tree control

Properties control

Accessibility shortcuts

Microsoft Natural Keyboard keys

Microsoft Natural Keyboard with IntelliType software installed

Dialog box keyboard commands

IPHONE Apps

Pandora Radio

Tune in.

Square

Get paid.

How to use a computer

Laptop-size

Thumb-sized

Numeric

Non-standard or special-use types

Chorded

Software

Foldable

Projection/Laser

Optical keyboard technology

Top 100 companies

What is a database

Database and why it is important

What is Webmail (or Web-based e-mail)

Contents

[edit] History

[edit] Software packages

[edit] Rendering and compatibility

What is stand by mode on a computer

Computers

[edit] Sleep Mode Testing

[edit] See also

Web Site Hosting

What is a GIF Image

What are JPEG Images

NIC Card

Contents

[edit] History

[edit] Standardization

[edit] General description

[edit] Dealing with multiple clients

[edit] CSMA/CD shared medium Ethernet

[edit] Main procedure

[edit] Collision detected procedure

[edit] Repeaters and hubs

[edit] Bridging and switching

[edit] More advanced networks

[edit] Autonegotiation and duplex modes

[edit] Physical layer

[edit] Ethernet frame types and the EtherType field

[edit] Runt frames

[edit] Varieties of Ethernet

[edit] Related standards

[edit] See also

[edit] Notes

Web Server

Contents

[edit] Overview

[edit] History of web servers

[edit] Common features

[edit] Path translation

[edit] Load limits

[edit] Kernel-mode and user-mode Web servers

[edit] Overload causes

[edit] Overload symptoms

[edit] Anti-overload techniques

[edit] Market structure

[edit] See also

[edit] References