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Latest Computer Technology

2009-02-02T19:03:00.000-08:00

What do you think these are???

Look very closely and guess what they could be...

PENS WITH HIDDEN CAMS???

any wild guesses now???

no clue???...

congratulations! you've now looked into the future...

you're looking at something that will replace your PC in

the future....

NOW LOOK AT THIS...

In the revolution of miniature computers, the scientists

are ahead with bluetooth technology... the forthcoming computers within your pockets .

These pen instruments produce both the monitor as well

as the keyboard on flat surfaces, where you can just

carry out the normal operations you do on your desktop.

What is a DNA Computer?

2008-12-31T06:50:00.000-08:00

DNA computers will be the next-generation computers made of genes' building blocks. Because of their speed, miniaturization and data storage potential DNA computers are being considered as a replacement for silicon-based computers। Current DNA computer research has already proven that DNA computers are capable of solving complex mathematical equations and storing enormous amounts of data.

Limitation of Silicon Chips

Silicon-based computer chips have been around for more than 40 years and manufacturers have been successful in making silicon-based chips smaller, more complex and faster than their predecessors. According to Moore's Law, microprocessor size is halved every eighteen months. However, there is a limitation to how small, fast and compact silicon computer chips can be.

Advantages of DNA Computers

DNA computers show promise because they do not have the limitations of silicon-based chips. For one, DNA based chip manufacturers will always have an ample supply of raw materials as DNA exists in all living things; this means generally lower overhead costs. Secondly, the DNA chip manufacture does not produce toxic by-products. Last but not the least, DNA computers will be much smaller than silicon-based computers as one pound of DNA chips can hold all the information stored in all the computers in the world.

With the use of DNA logic gates, a DNA computer the size of a teardrop will be more powerful than today's most powerful supercomputer. A DNA chip less than the size of a dime will have the capacity to perform 10 trillion parallel calculations at one time as well as hold ten terabytes of data. The capacity to perform parallel calculations, much more trillions of parallel calculations, is something silicon-based computers are not able to do. As such, a complex mathematical problem that could take silicon-based computers thousands of years to solve can be done by DNA computers in hours. For this reason, the first use of DNA computers will most probably be cracking of codes, route planning and complex simulations for the government.

History of DNA Computers

The first person who thought of and experimented with DNA as an alternative to silicon chips was Leonard Adleman, a computer scientist working in the University of Southern California. The 1994 experiment using DNA as a way of solving complex mathematical problems was a product of a book's influence (Molecular Biology of the Gene written by James Watson).

DNA computers will work through the use of DNA-based logic gates। These logic gates are very much similar to what is used in our computers today with the only difference being the composition of the input and output signals. In the current technology of logic gates, binary codes from the silicon transistors are converted into instructions that can be carried out by the computer. DNA computers, on the other hand, use DNA codes in place of electrical signals as inputs to the DNA logic gates. DNA computers are, however, still in its infancy and though it may be very fast in providing possible answers, narrowing these answers down still takes days.

-www.tech-faq.com-

Palm Computers

2008-12-31T06:49:00.000-08:00

A Palm Computer (also called a PalmPilot) is, in a nutshell, a computer the size of a pop-tart. It has a an 8Mhz processor and 1MB of memory- that's as much power as most desktop computers had a few years ago. So anything you could do with your computer in 1992 you can do in your hand in 1998.

Right out of the box you can store phone numbers and to-do lists, take short notes, and schedule alarms and your appointments। Data is entered on to the touch screen using a small pen, or imported from your desk computer through a cable included in the package. When you add other software you can view maps and pictures, play games, read E-books, and more.

-smasher.com-

notebook computer

2008-12-31T06:39:00.000-08:00

An extremely lightweight personal computer. Notebook computers typically weigh less than 6 pounds and are small enough to fit easily in a briefcase. Aside from size and portability, the principal difference between a notebook computer and a personal computer is the display screen. Notebook computers use a variety of techniques, known as flat-panel technologies, to produce a lightweight and non-bulky display screen.

The quality of notebook display screens varies considerably. Many notebook display screens are limited to VGA resolution. Active-matrix screens produce very sharp images, but they do not refresh as rapidly as full-size monitors.

In terms of computing power, modern notebook computers are nearly equivalent to personal computers. They have the same CPUs, memory capacity, and disk drives. However, all this power in a small package is expensive.

Notebook computers come with battery packs that enable you to run them without plugging them in। However, the batteries need to be recharged every few hours.

-webopedia-

Laptop

2008-12-31T06:30:00.000-08:00

A laptop computer, also known as a notebook computer, is a small personal computer designed for mobile use. A laptop integrates all of the typical components of a desktop computer, including a display, a keyboard, a pointing device (a touchpad, also known as a trackpad, or a pointing stick) and a battery into a single portable unit. The rechargeable battery is charged from an AC/DC adapter and has enough capacity to power the laptop for several hours.

A laptop is usually shaped like a large notebook with thickness of 0.7–1.5 inches (18–38 mm) and dimensions ranging from 10x8 inches (27x22cm, 13" display) to 15x11 inches (39x28cm, 17" display) and up. Modern laptops weigh 3 to 12 pounds (1.4 to 5.4 kg), and some older laptops were even heavier. Most laptops are designed in the flip form factor to protect the screen and the keyboard when closed.

Originally considered "a small niche market"^[1] and perceived as suitable for "specialized field applications" such as "the military, the Internal Revenue Service, accountants and sales representatives"^[1]^[2], battery-powered portables had just 2% worldwide market share in 1986^[3]. But today, there are already more laptops than desktops in the enterprise^[4] and, according to a forecast by Intel, more laptops than desktops will be sold in the general PC market as soon as 2009^[5]।

History

The Epson HX-20

As the personal computer became feasible in the early 1970s, the idea of a portable personal computer followed; in particular, a "personal, portable information manipulator" was envisioned by Alan Kay at Xerox PARC in 1968^[6] and described in his 1972 paper as the "Dynabook"^[7].

The first commercially available portable computer appeared nine years later, in 1981. The Osborne 1 weighed 23.5 pounds (10.7 kg). It had no battery, a tiny 5" CRT screen and dual 5¼" single-density floppy drives. In the same year the first laptop-sized portable computer, the Epson HX-20, was announced^[8]. The Epson had a LCD screen, a rechargeable battery and a calculator-size printer in a 1.6 kg (4 pounds) enclosure.

The first laptop using the clamshell design, utilized today by almost all laptops, appeared in 1982. The $8150 GRiD Compass 1100 was purchased by NASA and the military among others. The Gavilan SC, released in 1983, was the first notebook marketed using the term "laptop".

From 1983 onwards:

Several new input methods were introduced: the touchpad (Gavilan SC, 1983), the pointing stick (IBM ThinkPad 700, 1992) and handwriting recognition (Linus Write-Top^[9], 1987).
CPUs became designed specifically for laptops (Intel i386SL, 1990), targeting low power consumption, and were augmented with dynamic power management features (Intel SpeedStep and AMD PowerNow!).
Displays reached VGA resolution by 1988 (Compaq SLT 286) and 256-color screens by 1993 (PowerBook 165c), progressing quickly to millions of colors and high resolutions.
High-capacity hard drives and optical storage (CD-ROM followed by DVD) became available in laptops soon after their introduction to the desktops.

Early laptops often had proprietary and incompatible architectures, operating systems and bundled applications.

Classification

The general terms "laptop" or "notebook" can be used to refer to a number of classes of small portable computers:^[10]^[11]

By purpose and (approximately) by screen size:

Desktop replacement - emphasizes performance, is less portable, 15" and larger screen;
Standard laptop - balances portability and features, 13-15" screen;
Subnotebook - emphasizes portability, has less features, 13" or smaller screen.

By features:

Budget - a cheap, lower-performance standard-sized laptop;
Tablet PC - Has a touch-screen interface, may or may not have a keyboard;
Netbook - A cheaper, smaller version of a subnotebook designed mainly for Internet surfing and basic office applications.
Rugged - Engineered to operate in tough conditions (strong vibrations, extreme temperatures, wet and dusty environments).

As replacement

An Apple 17" MacBook Pro is often used as a desktop replacement.

A desktop replacement computer is a laptop that provides most of the capabilities of a desktop computer, with a similar level of performance. Desktop replacements are usually larger and heavier than standard laptops. They contain more powerful components and numerous ports, and have a 15.4" or larger display. Because of their bulk, they are not as portable as other laptops and their operation time on batteries is typically shorter.^[11]

Some laptops in this class use a limited range of desktop components to provide better performance for the same price at the expense of battery life; in a few of those models, there is no battery at all, and the laptop can only be used when plugged in. These are sometimes called desknotes, a portmanteau of the words "desktop" and "notebook," though the term can also be applied to desktop replacement computers in general.^[12]

The names "Media Center Laptops" and "Gaming Laptops" are also used to describe this class of notebooks.^[10]

Subnotebook

Sony VAIO C1 subnotebook.

A subnotebook, also called an ultraportable by some vendors, is a laptop designed and marketed with an emphasis on portability (small size, low weight and long battery life) that retains the performance of a standard notebook. Subnotebooks are usually smaller and lighter than standard laptops, weighing between 0.8 and 2 kg (2 to 5 pounds)^[10]; the battery life can exceed 10 hours^[13] when a large battery or an additional battery pack is installed.

To achieve the size and weight reductions, ultraportables use high resolution 13" and smaller screens (down to 6.4"), have relatively few ports, employ expensive components designed for minimal size and best power efficiency, and utilize advanced materials and construction methods. Some subnotebooks achieve a further portability improvement by omitting an optical/removable media drive; in this case they may be paired with a docking station that contains the drive and optionally more ports or an additional battery.

The term "subnotebook" is usually reserved to laptops that run general-purpose desktop operating systems such as Windows, Linux or Mac OS X, rather than specialized software such as Windows CE, Palm OS or Internet Tablet OS.

Netbook

An Asus Eee PC netbook.

Main article: Netbook

A netbook is a small laptop designed for portability and low price, with a performance inferior to that of a standard notebook yet adequate for surfing on the Internet and basic word processing. Netbooks use 10" and smaller screens, weigh 0.6 to 1.2 kg (1.5 to 3 pounds), and are generally powered by a CPU from one of the low-cost families with a high performance-to-power ratio such as Intel Atom, Celeron ULV, or VIA C7 processors.^[14]

Netbooks use general-purpose operating systems such as Linux or Windows XP. Some models use small-capacity (4 to 40 Gb) SSD drives instead of the usual HDDs to save weight and battery power.

Rugged Laptop

A Panasonic Toughbook.

A rugged (or ruggedized) laptop is designed to reliably operate in harsh usage conditions such as strong vibrations, extreme temperatures and wet or dusty environments. Rugged laptops are usually designed from scratch, rather than adapted from regular consumer laptop models. Rugged notebooks are bulkier, heavier, and much more expensive than regular laptops^[15], and thus are seldom seen in regular consumer use.

The design features found in rugged laptops include rubber sheeting under the keyboard keys, sealed port and connector covers, passive cooling, superbright displays easily readable in daylight, cases and frames made of magnesium alloys or have a magnesium alloy rollcage^[16] that are much stronger than plastic found in commercial laptops and solid-state storage devices or hard disc drives that are shock mounted to withstand constant vibrations. Rugged laptops are commonly used by public safety services (police, fire and medical emergency), military, utilities, field service technicians, construction, mining and oil drilling personnel. Rugged laptops are usually sold to organizations, rather than individuals, and are rarely marketed via retail channels.

Components

Miniaturization: a comparison of a desktop computer motherboard (ATX form factor) to a motherboard from a 13" laptop (2008 unibody Macbook)

Inner view of a Sony Vaio laptop

The basic components of laptops are similar in function to their desktop counterparts, but are miniaturized, adapted to mobile use, and designed for low power consumption. Because of the additional requirements, laptop components have worse performance than desktop parts of comparable price. Furthermore, the design bounds on power, size, and cooling of laptops limit the maximum performance of laptop parts compared to that of desktop components. ^[17]

The following list summarizes the differences and distinguishing features of laptop components in comparison to desktop personal computer parts:

Motherboard - laptop motherboards are highly make- and model-specific, and do not conform to a desktop form factor. Unlike a desktop board that usually has several slots for expansion cards (3 to 7 are common), a board for a small, highly integrated laptop may have no expansion slots at all, with all the functionality implemented on the motherboard itself; the only expansion possible in this case is via an external port such as USB. Other boards may have one or more standard or proprietary expansion slots. Several other functions (storage controllers, networking, sound card and external ports) are implemented on the motherboard.^[18]

Central processing unit (CPU) - Laptop CPUs have advanced power-saving features and produce less heat than desktop processors, but are not as powerful.^[19] There is a wide range of CPUs designed for laptops available from Intel (Pentium M, Celeron M, Intel Core and Core 2 Duo), AMD (Athlon, Turion 64, and Sempron), VIA Technologies, Transmeta and others. On the non-x86 architectures, Motorola and IBM produced the chips for the former PowerPC-based Apple laptops (iBook and PowerBook). Some laptops have removable CPUs, although support by the motherboard may be restricted to the specific models.^[20] In other laptops the CPU is soldered on the motherboard and is non-replaceable.

A SODIMM memory module.

Memory (RAM) - SO-DIMM memory modules that are usually found in laptops are about half the size of desktop DIMMs.^[18] They may be accessible from the bottom of the laptop for ease of upgrading, or placed in locations not intended for user replacement such as between the keyboard and the motherboard.

Expansion cards - A PC Card (formerly PCMCIA) or ExpressCard bay for expansion cards is often present on laptops to allow adding and removing functionality, even when the laptop is powered on. Some subsystems (such as Wi-Fi or a cellular modem) can be implemented as replaceable internal expansion cards, usually accessible under an access cover on the bottom of the laptop. Two popular standards for such cards are MiniPCI and its successor, the PCI Express Mini. ^[21]

Power supply - laptops are powered by an internal rechargeable battery that is charged using an external power supply. The power supply can charge the battery and power the laptop simultaneously; when the battery is fully charged, the laptop continues to run on AC power. The charger adds about 400 grams (1 lb) to the overall "transport weight" of the notebook.

Battery - Current laptops utilize lithium ion batteries, with more recent models using the new lithium polymer technology. These two technologies have largely replaced the older nickel metal-hydride batteries. Typical battery life for standard laptops is two to five hours of light-duty use, but may drop to as little as one hour when doing power-intensive tasks. Batteries' performance gradually decreases with time, leading to an eventual replacement in one to five years, depending on the charging and discharging pattern. This large-capacity main battery should not be confused with the much smaller battery nearly all computers use to run the real-time clock and to store the BIOS configuration in the CMOS memory when the computer is off.

Video display controller - on standard laptops video controller is usually integrated into the chipset. This tends to limit the use of laptops for gaming and entertainment, two fields which have constantly escalating hardware demands^[22]. Higher-end laptops and desktop replacements in particular often come with dedicated graphics processors on the motherboard or as an internal expansion card. These mobile graphics processors are comparable in performance to mainstream desktop graphic accelerator boards.^[23]

Display - Most modern laptops feature 12 inch (30 cm) or larger color active matrix displays with resolutions of 1024×768 pixels and above. Many current models use screens with higher resolution than typical for desktop PCs (for example, the 1440×900 resolution of a 15" Macbook Pro^[24] can be found on 19" widescreen desktop monitors).

A size comparison of 3.5" and 2.5" hard disk drives

Removable media drives - a DVD/CD reader/writer drive is standard. CD drives are becoming rare, while Blu-Ray is not yet common on notebooks^[25]. Many ultraportables and netbooks either move the removable media drive into the docking station or exclude it altogether.

Internal storage - Hard disks are physically smaller—2.5 inch (60 mm) or 1.8 inch (46 mm) —compared to desktop 3.5 inch (90 mm) drives. Some new laptops (usually ultraportables) employ more expensive, but faster, lighter and power-efficient Flash memory-based SSDs instead. Currently, 250 to 320 Gb sizes are common for laptop hard disks (64 to 128 Gb for SSDs).

Input - A pointing stick, touchpad or both are used to control the position of the cursor on the screen, and an integrated keyboard is used for typing. External keyboard and mouse may be connected using USB or PS/2 (if present).

Ports - several USB ports, an external monitor port (VGA or DVI), audio in/out, and an Ethernet network port are found on most laptops. Less common are legacy ports such as a PS/2 keyboard/mouse port, serial port or a parallel port. S-video or composite video ports are more common on consumer-oriented notebooks.

Docking stations

A docking station is a relatively bulky laptop accessory that contains multiple ports, expansion slots and bays for fixed or removable drives. A laptop connects and disconnects easily to a docking station, typically through a single large proprietary connector. A port replicator is a simplified docking station that only provides connections from the laptop to input/output ports. Both docking stations and port replicators are intended to be used at a permanent working place (a desk) to offer instant connection to multiple input/output devices and to extend a laptop's capabilities.

Docking stations became a common laptop accessory in the early 1990s. The most common use was in a corporate computing environment where the company had standardized on a common network card and this same card was placed into the docking station. These stations were very large and quite expensive. As the need for additional storage and expansion slots became less critical because of the high integration inside the laptop, the "port replicator" has gained popularity. The port replicator was a cheaper, often passive device that simply mated to the connectors on the back of the notebook and allowed the user to quickly connect his laptop so that his monitor, keyboard, printer and other devices were instantly attached. As higher speed ports such as USB and Firewire became common, the connection of a port replicator to a laptop was accomplished by a small cable connected to one of the USB or FireWire ports on the notebook. Wireless Port Replicators are available as well.

A recent variant of the port replicator is the combined power/display/USB hub cable found in the new Apple Cinema Display^[26].

Standards

Some laptop components (optical drives, hard drives, memory and internal expansion cards) are relatively standardized, and it is possible to upgrade or replace them in many laptops as long as the new part is of the same type.^[21] Subtle incompatibilities and variations in dimensions, however, are not uncommon.^[27] Depending on the manufacturer and model, a laptop may range from having several standard, easily customizable and upgradeable parts to a proprietary design that can't be reconfigured at all.

In general, components other than the four categories listed above are not intended to be replaceable, and thus rarely follow a standard. In particular, motherboards, locations of ports, design and placement of internal components are usually make- and model-specific. Those parts are neither interchangeable with parts from other manufacturers nor upgradeable. If broken or damaged, they must be substituted with an exact replacement part. The users uneducated in the relevant fields are those the most affected by incompatibilities, especially if they attempt to connect their laptops with incompatible hardware or power adapters.

Intel, Asus, Compal, Quanta and other laptop manufacturers have created the Common Building Block standard for laptop parts to address some of the inefficiencies caused by the lack of standards.

Advantages

Laptop computers are portable and can be used in many locations (Former Mexican President, Vicente Fox).

Portability is usually the first feature mentioned in any comparison of laptops versus desktop PCs^[28]. Portability means that a laptop can be used in many places - not only at home and at the office, but also during commuting and flights, in coffee shops, in lecture halls and libraries, at clients' location or at a meeting room, etc. The portability feature offers several distinct advantages:

Getting more done - using a laptop in places where a desktop PC can't be used, and at times that would otherwise be wasted. For example, an office worker tackling his e-mails during an hour-long commute by train, or a student doing her homework at the university coffee shop during a break between lectures.^[29]

Immediacy - Carrying a laptop means having instant access to various information, personal and work files. Immediacy allows better collaboration between coworkers or students, as a laptop can be flipped open to present a problem or a solution anytime, anywhere.

Up-to-date information - If a person has more than one desktop PC, a problem of synchronization arises: changes made on one computer are not automatically propagated to the others. There are ways to resolve this problem, including physical transfer of updated files (using a USB stick or CDs) or using synchronization software over the Internet. However, using a single laptop at both locations avoids the problem entirely, as the files exist in a single location and are always up-to-date.

Connectivity - A proliferation of Wi-Fi wireless networks and cellular broadband data services (HSDPA, EVDO and others) combined with a near-ubiquitous support by laptops ^[30] means that a laptop can have easy Internet and local network connectivity while remaining mobile. Wi-Fi networks and laptop programs are especially widespread at university campuses.^[31]

Other advantages of laptops include:

Size - laptops are smaller than standard PCs. This is beneficial when space is at a premium, for example in small apartments and student dorms. When not in use, a laptop can be closed and put away.

Low power consumption - laptops are several times more power-efficient than desktops. A typical laptop uses 20-90 W, compared to 100-800 W for desktops. This could be particularly beneficial for businesses (which run hundreds of personal computers, multiplying the potential savings) and homes where there is a computer running 24/7 (such as a home media server, print server, etc.)

Quiet - laptops are often quieter than desktops, due both to better components (quieter, slower 2.5-inch hard drives) and to less heat production leading to use of fewer and slower cooling fans.

Battery - a charged laptop can run several hours in case of a power outage and is not affected by short power interruptions and brownouts. A desktop PC needs a UPS to handle short interruptions, brownouts and spikes; achieving on-battery time of more than 20-30 minutes for a desktop PC requires a large and expensive UPS.^[32]

Disadvantages

Compared to desktop PCs, laptops have disadvantages in the following fields:

Performance

While the performance of mainstream desktops and laptops is comparable, laptops are significantly more expensive than desktop PCs at the same performance level.^[33] The upper limits of performance of laptops are a little bit lower, and "bleeding-edge" features usually appear first in desktops and only then, as the underlying technology matures, are adapted to laptops.

However, for Internet browsing and typical office applications, where the computer spends the majority of its time waiting for the next user input, even netbook-class laptops are generally fast enough.^[34] Standard laptops are sufficiently powerful for high-resolution movie playback, 3D gaming and video editing and encoding. Number-crunching software (databases, math, engineering, financial, etc.) is the area where the laptops are at the biggest disadvantage.

Upgradeability

Upgradeability of laptops is very limited compared to desktops, which are thoroughly standardized. In general, hard drives and memory can be upgraded easily. Optical drives and internal expansion cards may be upgraded if they follow an industry standard, and all other internal components, including the CPU and graphics, are not intended to be upgradeable.

The reasons for limited upgradeability are both technical and economic. There is no industry-wide standard form factor for laptops; each major laptop manufacturer pursues its own proprietary design and construction, with the result that laptops are difficult to upgrade and have high repair costs. With few exceptions, laptop components can rarely be swapped between laptops of competing manufacturers, or even between laptops from the different product-lines of the same manufacturer.

Some upgrades can be performed by adding external devices, either USB or in expansion card format such a PC Card: sound cards, network adapters, hard and optical drives, and numerous other peripherals are available. But those upgrades usually impair the laptop's portability, because they add cables and boxes to the setup and often have to be disconnected and reconnected when the laptop is moved.

Ergonomics and health

Laptop coaster preventing heating of lap and improving laptop airflow.

Because of their small and flat keyboard and trackpad pointing devices, prolonged use of laptops can cause RSI.^[35] Usage of ergonomic keyboards and pointing devices is recommended to prevent injury when working for long periods of time; they can be connected to a laptop easily by USB or via a docking station. Some health standards require ergonomic keyboards at workplaces.

The integrated screen often causes users to hunch over for a better view, which can cause neck or spinal injuries. A larger and higher-quality external screen can be connected to almost any laptop to alleviate that and to provide additional "screen estate" for more productive work.

A study by State University of New York researchers found that heat generated from laptops can raise the temperature of the scrotum, potentially putting sperm count at risk. The small study, which included little more than two dozen men aged 13 to 35, found that the sitting position required to balance a laptop can raise scrotum temperature by as much as 2.1 °C (3.8 °F). Heat from the laptop itself can raise the temperature by another 0.7 °C (1.4 °F), bringing the potential total increase to 2.8 °C (5.2 °F). However, further research is needed to determine whether this directly affects sterility in men.^[36]

A common practical solution to this problem is to place the laptop on a table or desk. Another solution is to obtain a cooling unit for the laptop, these units are usually USB powered consist of a hard thin plastic case housing 1, 2 or 3 cooling fans (the whole thing is designed to sit under a laptop) which results in the laptop remaining cool to the touch, and greatly reduces laptop heat generation. There are several companies which make these coolers.

Heat from using a laptop on the lap can also cause skin discoloration on the thighs.^[37]

Durability

A clogged heatsink on a 2.5 year old laptop.

Due to their portability, laptops are subject to more wear and physical damage than desktops. Components such as screen hinges, latches, power jacks^[38] and power cords deteriorate gradually due to ordinary use. A liquid spill onto the keyboard, a rather minor mishap with a desktop system, can damage the internals of a laptop and result in a costly repair. One study found that a laptop is 3 times more likely to break during the first year of use than a desktop.^[39]

Original external components are expensive (a replacement AC adapter, for example, could cost $75); other parts are inexpensive - a power jack can cost a few dollars - but their replacement may require extensive disassembly and reassembly of the laptop by a technician. Other inexpensive but fragile parts often cannot be purchased separate from larger more expensive components.^[40] The repair costs of a failed motherboard or LCD panel may exceed the value of a used laptop.

Laptops rely on extremely compact cooling systems involving a fan and heat sink that can fail due to eventual clogging by accumulated airborne dust and debris. Most laptops do not have any sort of removable dust collection filter over the air intake for these cooling systems, resulting in a system that gradually runs hotter and louder as the years pass. Eventually the laptop starts to overheat even at idle load levels. This dust is usually stuck inside where casual cleaning and vacuuming cannot remove it. Instead, a complete disassembly is needed to clean the laptop.

Battery life of laptops is limited; the capacity drops with time, necessitating an eventual replacement after a few years.

Security

Being expensive, common and portable, laptops are prized targets for theft. The cost of the stolen business or personal data and of the resulting problems (identity theft, credit card fraud, breach of privacy laws) can be many times the value of the stolen laptop itself. Therefore, both physical protection of laptops and the safeguarding of data contained on them are of the highest importance.

Most laptops have a Kensington security slot which is used to tether the computer to a desk or other immovable object with a security cable and lock. In addition to this, modern operating systems and third-party software offer disk encryption functionality that renders the data on the laptop's hard drive unreadable without a key or a passphrase.

Other portable computing devices

There are several categories of portable computing devices that can run on batteries but are not usually classified as laptops: portable computers, keyboardless tablet PCs, Internet tablets, PDAs, handheld computers (UMPCs) and smartphones.

The Compaq Portable

A keyboard-less tablet PC

A Palm TX PDA

A Nokia N800 Internet tablet

An OQO handheld computer

An Apple iPhone smartphone

A Portable computer is a general-purpose computer that can be easily moved from place to place, but cannot be used while in transit, usually because it requires some "setting-up" and an AC power source. The most famous example is the Osborne 1. Also called a "transportable" or a "luggable" PC.

A Tablet PC that lacks a keyboard (also known as a non-convertible Tablet PC) is shaped like slate or a paper notebook, features a touchscreen with a stylus and handwriting recognition software. Tablets may not be best suited for applications requiring a physical keyboard for typing, but are otherwise capable of carrying out most tasks that an ordinary laptop would be able to perform.

An Internet tablet is an Internet appliance in tablet form. Unlike a Tablet PC, an Internet tablet does not have much computing power and its applications suite is limited - it can not replace a general purpose computer. Internet tablets typically feature an MP3 and video player, a web browser, a chat application and a picture viewer.

A Personal digital assistant (PDA) is a small, usually pocket-sized, computer with limited functionality. It is intended to supplement and to synchronize with a desktop computer, giving access to contacts, address book, notes, e-mail and other features.

A Handheld computer, also known as an Ultra Mobile PC (UMPC) is a full-featured, PDA-sized computer running a general-purpose operating system.

A Smart phone is a PDA with an integrated cellphone functionality. Current smartphones have a wide range of features and installable applications.

Boundaries that separate these categories are blurry at times. For example, the OQO UMPC is also a PDA-sized tablet PC; the Apple eMate had the clamshell form factor of a laptop, but ran PDA software. The HP Omnibook line of laptops included some devices small enough to be called handheld computers. The hardware of the Nokia 770 internet tablet is essentially the same as that of a PDA such as the Zaurus 6000; the only reason it's not called a PDA is that it doesn't have PIM software. On the other hand, both the 770 and the Zaurus can run some desktop Linux software, usually with modifications.

Major brands and manufacturers

There is a multitude of laptop brands and manufacturers; several major brands, offering notebooks in various classes, are listed in the box to the right.

The major brands usually offer good service and support, including well-executed documentation and driver downloads that will remain available for many years after a particular laptop model is no longer produced. Capitalizing on service, support and brand image, laptops from major brands are more expensive than laptops by smaller brands and ODMs.

Some brands are specializing in a particular class of laptops, such as gaming laptops (Alienware), netbooks (EeePC) and laptops for children (OLPC).

Many brands, including the major ones, do not design and do not manufacture their laptops. Instead, a small number of Original Design Manufacturers (ODMs) design new models of laptops, and the brands choose the models to be included in their lineup. In 2006, 7 major ODMs manufactured 7 of every 10 laptops in the world, with the largest one (Quanta Computer) having 30% world market share.^[41] Therefore, there often are identical models available both from a major label and from a low-profile ODM in-house brand.

Motherboard

2008-11-23T19:31:00.000-08:00

What is a Motherboard?

The motherboard is the main circuit board inside your PC. Every components at some point communicates through the motherboard, either by directly plugging into it or by communicating through one of the motherboards ports. The motherboard is one big communication highway. Its purpose inside your PC is to provide a platform for all the other components and peripherals to talk to each other.

Types of Motherboards

The type of motherboards depends on the CPU it was designed for. You can therefore categories motherboards by which socket type they have. e.g. Socket A, Socket 478 etc. The Type of motherboard you buy is very important, as it will need to house your CPU, and they are not interchangeable. When buying a motherboard, it will always tell you what socket type it has.

When Buying a Motherboard

As everything you have on the PC at some point needs the motherboard, you need to consider these components when buying a motherboard. Foe example, if you have a lot of devices with a PCI interface that you wish to use, there is little point buying a motherboard that only offers you 3 PCI slots. Like wise with memory, you have to make sure that there are enough slots for the amount of memory you have or wish to have.

The motherboard also needs the correct type of interface for your Memory, Graphics card, Hard disks and other items as well. You will find that most motherboards offer everything you need however it needs checking on when buying. Its especially important to pay detail to your motherboard if you want to use older components, which a new motherboard may or may not support.

The major difference between motherboards that support the same CPU is the model of the chipset (more on the chipset later). Different chipsets offer different performance and different features in terms of memory support, AGP port speed, Multiplier numbers, Bus speeds and much more.

Speed of a Motherboard

Motherboards have got to be one of the hardest components to measure the speed of. Performance can really only be measured by benchmarking using the same components in several motherboards of the same type. You often find that motherboards with the same chipset have roughly the same performance in real world tests. The minor differences that do occur are down to the quality of the materials used and the quality of the manufacturing.

The Motherboards speeds that are quoted on the box are maximum supported speeds for other components. For example motherboards will quote the maximum FSB (Front Side Bus) speed. However without a CPU that also supports this speed, it will never be reached. Likewise when it quotes the maximum memory speed. The memory of this speed has to be present.

What is a Motherboard Chipset?

A motherboard chipset controls all the data that flows through the data channels (buses) of the motherboard. The primary function of the motherboard chipset is to direct this data to the correct area's of the motherboard, and therefore the correct components.

Components of a Motherboard

The motherboard contains many connections for all type of components. Motherboards contain expansion slots such as the ISA, PCI, AGP and DIMM sockets. It also contains external connections for your onboard sound card, USB ports, Serial and Parallel ports, PS/2 ports for your keyboard and mouse as well as network and Firewire connections.

So the motherboard has a massive part to play in the workings of your PC. Components that you buy all rely on the motherboard to have the correct connections are available and working. Its best to buy a decent motherboard especially if you plan on buying extra's in the future.

Did You Know?

Most computer dealers say they build their computers. If they carry a 3 year warranty they are built by someone else or the warranty is out of their back pocket. Very few parts outside of monitors carry anything pass one year, a few motherboards and even less hardrives carry a 3 year warranty.
Integrated Motherboard: A motherboard where some or all of the internal input or output devices are soldered into it.
Motherboard was the original name of the what is now called "main board." The difference is that motherboards had "daughter boards" plugged into them. These "daughter boards" later became simply "cards." Most brands of "main boards" have no cards, some don't even have plug-in slots for such.
Integrated motherboards cause problems when wanting to upgrade your computer, also, LOTS more money. EXAMPLE: Most Compaq /HPs, Dells, Gateways, IBMs have only three pieces usable in an upgrade: the CD ROM ($25 new), hard drive (usually too small to be used, $65-$95 new) and the 3.5" drive ($10 new).
The motherboard is the main board in a computer that supports the processor (CPU) and all internal input and output devices. Input and output devices are the video, modem, sound card, hard drive and floppy controllers, memory (RAM), network cards. All modern PCI motherboards, thanks to Intel, contain integrated floppy and IDE hard drive controllers. Again thanks to Intel & Via almost all motherboard now have integrated sound also. Luckily we can disable the on-board sound and put in a real Sound Blaster sound card.
Compaq/HP, Gateway, Acer, IBM, Pionex, Dell, NEC, Sony and Packard Bell computers make good landfill after crushing. That is if they have biodegradable motherboards. A case of Samsung and most Maxtor hard drives make fair boat anchors.

Consider the desk-and-file-cabinet metaphor for a moment. Imagine what it would be like if every time you wanted to look at a document or folder you had to retrieve it from the file drawer. It would slow you down tremendously, not to mention drive you crazy. With adequate desk space - our metaphor for memory - you can lay out the documents in use and retrieve information from them immediately, often with just a glance. Here's another important difference between memory and storage: the information stored on a hard disk remains intact even when the computer is turned off. However, any data held in memory is lost when the computer is turned off. In our desk space metaphor, it's as though any files left on the desk at closing time will be thrown away.

Did You Know?

For years, computer scientists and marketing types have abused the metric system when it comes to quantifying things like computer memory, disk space, etc. The reason for this is that in general computers are binary systems, and they work with powers of two. For the most part, this works fine, but once you start counting high enough, it becomes cumbersome to say that your computer has 1,073,741,824 (230) bytes of memory in it. So, it became common practice to shorten things by using the metric prefixes "kilo", "mega", "giga", "tera", etc.
To boost performance, (In most cases); Bigger and better RAM would be a better upgrade as opposed to bigger and better CPU.
In many cases same amount of RAM chips can still have difference in performance depending on thier bus speed. This bus speed is expressed in Megahertz as in 133MHz.

Inside every hard drive are small round disk-like objects made of either an aluminum/alloy or a glass/ceramic composite, these are called platters, each platter is coated with a special magnetic coating enabling them to store data magnetically.

Hovering above these platters are read/write heads that transfer data to and from the platters.

Hard Drive Capacities

Hard drives come with many different storage capacities, hard drive capacity is measured in bytes, with common capacities being stated in MB (Megabytes) and GB (Gigabytes).

To understand these figures correctly you need to know the basics of how data is stored/processed in digital systems such as PCs.

Digital data is a series of 1's (ones) and 0's (zeros) which are referred to as bits (Binary digITS), a byte is made up of 8 of these bits, so a single byte of data may look like 01001011 (8 consecutive bits).

1 Bit = either a 0 (zero) or a 1 (one)
1 Byte = 8 bits
1 KB (Kilobyte) = 1024 bytes (2¹⁰)
1 MB (Megabyte) = 1024 Kilobytes (2²⁰)
1 GB (Gigabyte) = 1024 Megabytes (2³⁰)
1 TB (Terabyte) = 1024 Gigabytes (2⁴⁰)

In the old days it was common to find hard drives with a capacity of just 5MB, nowadays it is hard to buy a new hard drive with less than 40GB, that's 40,960 Megabytes !

Common hard drive capacities these days range from 40GB up to and exceeding 120GB.

As a real world example let's take a color photo, and let's say the photo takes up 500 Kilobytes of storage space on a hard drive, so if you had a 40GB hard drive you could potentially store up to 81,290 color photos.

This is obviously hypothetical due to the fact that on the hard drive you would need your operating system and programs which would take up some of the storage space, but you can see the point.

When you consider that an average letter written in a word processor is around 30KB it becomes apparent that the storage capacity of modern hard drives is massive!

Hard Drive RPM Speeds

You will often see hard drives advertised as being capable of a certain RPM (Revolutions Per Minute), this figure (as the name suggests) refers to how many times the spindle makes a complete 360? turn in any single minute.

The higher the RPM, the faster the data can be read from the platters, which increases overall performance.

RPM values range from about 5,400RPM to 12,000RPM and above.

Did You Know?

The very first production hard disk was the IBM 305 RAMAC (Random Access Method of Accounting and Control), introduced on September 13, 1956.
IBM 305 RAMAC had approximately five megabytes capacity.
The first hard disk drive designed in the 5.25" form factor used in the first PCs was the Seagate ST-506. It featured four heads and a 5 MB capacity. IBM bypassed the ST-506 and chose the ST-412--a 10 MB disk in the same form factor--for the IBM PC/XT, making it the first hard disk drive widely used in the PC and PC-compatible world.

Tips

"I see all these terms like "bytes", "megabytes" and kilobytes. I don't know a kilobyte from a dog bite. How are the size of files measured, anyway?"

A bit (short for "binary digit") is the smallest possible unit of information on a PC. A single bit can hold only one of two values: 0 or 1.

A byte (short for "binary term") is a unit of storage capable of holding a single character. On almost all modern computers, a byte is equal to 8 bits.

A kilobyte (KB) is 1,024 bytes.

A megabyte (MB) is 1,048,576 bytes, or 1024 kilobytes.

A gigabyte (GB) is 1,073,741,824 bytes, or 1024 megabytes.

A terabyte (TB) is 1,099,511,627,776 bytes, or 1024 gigabytes.

A floppy disk that can hold 1.44 megabytes, for example, is capable of storing approximately 1.4 million characters, or about 3,000 pages of information. An 8.4 gigabyte hard drive can store about 9 billion characters and can hold close to 18 million pages of information.

I received an error telling me I was low on memory. I checked My Computer and it shows I have plenty of megabytes left. What's the problem?

This is a very common misconception. Although many PC owners use the terms interchangeably, "memory" and "hard drive space" are two night and day different things.

Many users tend to confuse the terms "memory" and "drive space" and often use one when they actually mean the other. Extreme examples of this confusion have been folks who get "out of memory" errors and run out and buy hard drives, and those who purchase SIMMs expecting the upgrade to add additional megabytes of storage space in which they can install software programs.

Memory refers to the amount of RAM (Random Access Memory) installed in the PC, whereas hard drive space is referring to the available amount of storage capacity on the PC's hard disk(s).

One analogy that has often been used to clarify the difference that I find works well is to compare the computer to an office that contains a desk, a file cabinet, and a bulletin board.

Storage space on your hard drive is like a "filing cabinet" where work is stored when not in use.

L2 Cache memory is like a "bulletin board" making the work at the "desk" go faster by keeping frequently used items close at hand.

RAM memory is like a "desk" with current work open on it and readily accessible.

Using the analogy above, the file cabinet represents the computer's hard disk, which provides high-capacity storage. This is where your data (work) is stored when not in use. Your memory (RAM) is the desk where what you are working on at the moment is found. When you want to do some work you take the files out of the filing cabinet (i.e. open a program) and put them on the desk.

Upgrading memory is like buying a larger desk. It will give you the ability to work on more files at one time and as there is more room to operate your system will perform a bit better. This does NOT however increase your storage space for files not in use, for that you have to buy a second filing cabinet (hard drive).

Another key difference between memory and hard drive space is that the data stored on a hard disk is not lost when the PC is turned off. This is not the case with memory however, any information held in memory is cleared when the computer is turned off. Again using the office analogy this would be equivalent to saying that any files you leave on your desk after 5PM will be tossed out by the cleaning crew. This is why occasionally saving work in process is such a good idea.

To take our office example yet one step further, if the desk and the filing cabinet helps us to understand the relationship between RAM memory and a PC's hard disk then we can equate secondary (Level 2 or L2) cache memory to a bulletin board we may hang over our desk.

As we go back and forth taking files out of storage in the filing cabinet, working on them at our desk and returning them, we may choose to stick some of the information that we find we are referring to constantly up on our bulletin board. When you need that information rather than going all the way to the filing cabinet all you have to do is to look up on the bulletin board and there it is.

Primary and secondary cache memory serves in much the same way, storing frequently accessed data in a special area so that it is always close at hand and loads much faster when needed.

I bought a 6.4 GB hard drive. When I look at the size of the hard drive by using DriveSpace3 or Right-Clicking on Drive C in My Computer I get a total amount of 5.99 GB. Where is the rest of my space?

This has to do with the way nearly every hard drive manufacturer in existence calculates hard drive size. They all define 1 gigabyte = 1,000,000,000 bytes instead of the 1 gigabyte = 1,073,741,824 bytes which it *really* is.

This is called "binary" vs "decimal" sizes. If you look at the *fine print* you will always see "[Company X] defines 1 gigabyte as 1 billion bytes". This is standard industry practice, unfortunately were a drive manufacturer (Western Digital for example) to be *honest* about this then their drives as advertised would all appear smaller than the competitors, when in fact they would not be. Shoppers would be comparing "apples to oranges" rather than "apples to apples".

Put another way in reality your hard drive is 6400 million bytes rather than 6400 megabytes. A 6.4 GB drive is actually closer to a 6 GB drive when viewed from a *real world* standpoint.

I installed an 8.4GB hard drive on my Aptiva but when I check both DriveSpace3 and the Properties of the drive in My Computer the "pie chart" is one solid color, showing all free space. It also says that the drive is only 2 GB. What up with that?

DriveSpace3 is an older Windows application developed prior to the advent of FAT32, and nobody at Microsoft has chosen to inform it that partitions larger than 2 GB are now not only possible but the norm. DriveSpace compression is not supported under FAT32, this utility is provided only for use under FAT16 anyway.

As far as the Properties of hard drives in My Computer and Windows Explorer, on Win95 systems where Internet Explorer version 4.x and the Active Desktop Update have not been installed the Properties figures key off of the inaccurate DriveSpace3 utility. On Windows 98 systems and systems running Win95 OSR2 on which Internet Explorer version 4.x with the Active Desktop update has been installed the "pie chart" in My Computer will be accurate.

What is this "FAT" I keep hearing about? What FAT do I have and what difference does it make?

FAT stands for File Allocation Table. This is what your Windows operating system uses to locate files on your hard disk. Due to fragmentation, a file may be divided into many sections that are scattered around the disk...the FAT keeps track of all these pieces.

The only file system that the original version of Win95 is called VFAT, or FAT16. Windows 98 and the OSR2 versions of Win95 support both FAT16 and the more efficient FAT32.

The advantages of the FAT32 file system are:
Unlike FAT16 where one can create a 2GB maximum partition size one can create any size partition under FAT32
Smaller cluster sizes making for a much more efficient drive on which more files can be stored.

Other than adding a larger or second hard drive what can I do as far as freeing up some space? What can I delete as far as preloaded software? What shouldn't I delete?

Other than that the best thing I can tell is is "when in doubt, Rename":

Wherever possible you always want to uninstall software rather than deleting it outright, but unfortunately on older Aptivas many of the programs IBM preloaded feature no uninstall option at all, often there's no alternative except to delete unwanted programs.

To be 100% safe when deleting anything a good idea is to RENAME the folders you are thinking of deleting pending actual deletion. Right-Click on the folder in Explorer (ex: "CServe") > Click Rename > Change the name by one letter (ex: "XCserve"). This takes the files out of their normal path and "simulates" the effect of deleting the folder.

Run your system normally for a few days. If you get no errors, have no problems and everything works after that time send the folder to the Bin and flush. If you DO have any problems just change the name back.

CPU

2008-11-23T19:26:00.000-08:00

What is Central Processing Unit (CPU)?

Sometimes we refer to the CPU as the system box or brain. It is the computer chip that does all of the processing for the computer. Inside this tiny chip are millions of transistors (electrical switches) that are connected so they can carry out mathematical calculations. Everything a computer does is essentially a mathematical calculation.

Did You Know?

The first single chip CPU was the Intel 4004, a 4-bit processor meant for a calculator (not Intel 8086). It processed data in 4 bits, but its instructions were 8 bits long. Program and Data memory were separate, 1K data memory and a 12-bit PC for 4K program memory (in the form of a 4 level stack, used for CALL and RET instructions). There were also sixteen 4-bit (or eight 8-bit) general purpose registers.
The 4004 had 46 instructions, using only 2,300 transistors in a 16-pin DIP. It ran at a clock rate of 740kHz (eight clock cycles per CPU cycle of 10.8 microseconds) - the original goal was 1MHz, to allow it to compute BCD arithmetic as fast (per digit) as a 1960's era IBM 1620.
The 4040 (1972) was an enhanced version of the 4004, adding 14 instructions, larger (8 level) stack, 8K program space, and interrupt abilities (including shadows of the first 8 registers). Should Pioneer 10 and Pioneer 11 ever be found by an extraterrestrial species, the 4004 will represent an example of Earth's technology.
Then came Intel 8086 (1978) - This chip was skipped over for the original PC, but was used in a few later computers that didn't amount to much. It was a true 16-bit processor and talked with its cards via a 16 wire data connection. The chip contained 29,000 transistors and 20 address lines that gave it the ability to talk with up to 1 MB of RAM. What is interesting is that the designers of the time never suspected anyone would ever need more than 1 MB of RAM. The chip was available in 5, 6,, 8, and 10 MHz versions.
Intel was not the only manufacturer playing in the sandbox at the time. AMD put out its AM486 series in answer to Intel's counterpart. AMD released the chip in AM486DX4/75, AM486DX4/100, and AM486DX4/120 versions. It contained on-board cache, power management features, 3-volt operation and SMM mode. This made the chip fitting for mobiles in addition to desktops. The chip found its way into many 486-compatibles.

Tips

What benefit does it (MMX) offer users?

Desktop

Advantages: Excellent desk computer.
Great use of desk space when monitor is placed on top of the computer.
Disadvantages: With some types of desktop cases can be very difficult to upgrade.
Does not really work on the floor.
Recommendations: Excellent choice for a business and home user computer. End users planning to upgrade or place computer on floor we recommend going with tower computer unless manufacturer provides desktop to be converted to tower.

Style

I am getting tired of the standard looking case. I would like to find a case with style and possibly a clear case. Where can I find a company that can supply me a case like this?

There are several types of companies that manufacturer cases with more style as well as clear cases. You can find these as well as other case manufacturers on our Pricing Solution.

Basic Computer Network Information

2008-11-23T19:08:00.000-08:00

Introduction

A network is a group of things that are connected together. In a computer network, the things that are connected are computers, of course. A computer network can be as small as two computers but there is no maximum size, and many networks have hundreds or thousands of computers.

There are three main reasons for connecting computers in a network:

Share information. This can be messages such as e-mail, or it can be files that are stored on one computer and used by someone at a different computer.

Share resources. A printer that can be accessed from different computer systems is a shared resource. So is an Internet connection used by more than one computer.

Centralized control. In most offices, the management determines what the computers may be used for and what kind of resources and support they need. This is much easier to deal with if the computers are connected.

Types of Networks

Just as there is no limit to the number of systems in a network, there is also no limit to the geographical size of a network. As a practical matter though, there are some structural differences between a network of computers all in the same room, and a network connecting computers in Los Angeles to ones in Sydney Australia.

The most common network includes computers that are close together, usually in the same building or office. This is called a Local Area Network, abbreviated LAN.

The computers in a LAN are usually connected with cable made up of pairs of wires, but faster (and more expensive) cables are made from glass fibers, called fiber optic cable. A network may even use radio waves, in which case it is a wireless LAN.

When the computers being connected are far apart, typically in different cities, it is called a WAN or Wide Area Network. The connection is usually done with special high-speed lines leased from the phone company, but it is also possible to connect over an ordinary phone line using a device called a modem. It’s slow, but possible. Accessing a network through a phone line and modem is called a dial-up connection.

The biggest of all networks is the Internet. The backbone of the Internet consists of powerful computers all over the world with high-speed connections between them. Individual computers such as yours then connect to this backbone through an Internet Service Provider or ISP.

Ethernet

Most LANs in existence today use a technology called Ethernet. In an Ethernet network, every piece of information put on the network is seen by every other computer on the network, and each computer must determine if that information is meant for itself.

To make this work, before the information goes out on the network it is first broken up into small pieces called packets, and each packet has added to it the address of the computer that should receive it. The part of the packet containing the address is called the header.

Header

Packet diagram

Then, each computer looks at the address on each packet that comes by on the network cable, and copies the ones that have the right address. The computer that sent the packet is called the source, and the one that is supposed to receive it is called the destination.

Network Connections

When a packet comes out of the computer that originated it, that packet must have a complete electrical path to every other computer. The simplest way to do this is to have a cable that goes from one computer to the next until it has connected to each one. This is called a bus network.

Bus Network

A bus network is the simplest to explain and draw, but it’s not often the simplest one to use, especially if computers are distributed around various offices in a building, and then get added, taken away, moved around and so forth.

A much more practical way to connect more than a couple of systems is to connect each one to a device called a hub. Each system has a cable that goes from it to the hub, and inside the hub an electrical connection is made between all of the cables. Each place where a cable plugs into the hub is called a port.

5-port hub ports

To create larger networks, hubs can use one or more of their connections to connect to other hubs. This is called a star network, but as far as the electrical signals are concerned, they go from one computer to every other computer, no different than the bus network.

3-hub star network

When networks get really big, with 100s of systems or more, it’s no longer such a good idea to have each computer look at every packet, because almost none of the packets will be for that computer. The large network can be broken up into smaller groups called subnets, and these are connected with a device called a data switch, or just a switch.

Within each subnet, all of the computers still see every packet, and so does the switch. Normally the switch won’t pass those packets on to the other subnets, but if the packet has an address for a destination in another subnet, the switch will pass the packet to the port for that subnet. All of the systems in that subnet will then see the packet, including the system it is actually addressed to. In order to know where to send a packet, the switch must have a table of addresses for each subnet.

Switch with 4 subnets

The simplest form of a switch is called a bridge, and it connects just two subnets. A bridge only needs two ports then, one for each of the subnets.

Sometimes a network will be so big and complex that one switch isn’t enough to connect all of the subnets. In that case the subnet receiving a packet might be connected to a different switch than the subnet where the packet started. This is a more complicated problem, because the switch would need to know not only the packet’s destination, but also where to send it next to make sure it got there.

For this, a smarter device is needed, called a router. The router needs to know not only the subnet addresses, but also the best path, or route, to get from one to another.

Route path diagram

One place where routers are used in a big way is the Internet. If you send a message on the Internet, it might go through many routers before it reaches its destination. And when you surf to a website, all of the graphics and text showing up on your screen had to go through routers to find their way from the web site to your computer.

By the way, every LAN that connects to the Internet becomes a subnet of the Internet, even if it has its own internal subnets.

Clients and Servers

In addition to the various ways networked systems can be physically connected, there are two basic ways that network activities can be arranged. In one, all of the computers have equal status. This is called peer-to-peer, because a peer means someone (or something) that is the equal of another. Peer-to-peer is used mostly in very small networks of less than a dozen systems.

The more common arrangement is called client-server. One system, called the server, is responsible for a particular activity or resource. The other systems are called clients, and they go through the server when they want to use the function or resource that the server is responsible for.

Some of the things servers are commonly used for include network administration, e-mail, printers, file storage, and Internet access. Often several of these functions will be combined into one machine. There is no rule that says a network server and a print server can’t be the same system.

Clients Server

print server

There is also no rule that says a server must serve the entire network. It is usually convenient to have a separate network server for each subnet. There are other divisions that can occur even within a subnet. Computers that need to share the same resources can be organized into workgroups. With the Windows NT operating system, the LAN can be divided into sections called domains, and each domain needs its own server called a domain controller.

Protocols

A protocol is an agreed-upon standard for how something will be done. When your mother taught you to chew with your mouth closed and keep your elbows off the table, that was a protocol for proper dining. Computer protocols are the rules for connecting with other computers and exchanging information with them.

Ethernet is a protocol. Earlier we called it a technology, but it is also a set of rules for how that technology is used. If each piece of hardware and software complies with the rules, then information can be correctly transferred from one from one system to another in a LAN.

There are many protocols used in networking. There are some protocols that are used together with other protocols, where each one takes care of different aspects of networking. Sometimes two protocols do the same thing in different ways, and it is necessary to choose one or the other. The important thing is that both systems trying to communicate with each other have matching protocols that they can use.

TCP/IP

One very important set of protocols is called TCP/IP. It is important because it is what the creators of the Internet decided would be used for that particular network, which means that any computer that wants to connect to the Internet must also use TCP/IP. TCP/IP stands for Transmission Control Protocol / Internet Protocol.

TCP/IP is actually in two parts. The TCP portion covers the agreements between systems about how they will carry on their ‘conversation’, and the IP portion deals with addressing the packets and routing them.

The TCP part all happens in the background and we don’t really need to concern ourselves with it under normal circumstances. However, in a network that uses TCP/IP, every system must have a unique IP address, and that is something that requires human intervention in one way or another.

IP Addresses

An IP address is made up of four sets of numbers separated by periods. An example is:

192.168.42.122

Each of these sets of numbers is called an octet, because they started out as 8-digit binary numbers. By changing them into 3-digit decimal numbers, the whole address is shorter and easier to remember. The highest value for any octet is 255, because the highest number you can make with eight binary digits is equal to 255 in decimal.

In most networks, the first three octets are the same for all systems, and the last octet is different for every machine. If there are more than 255 computers in a network, it is usually divided into smaller subnets.

Static or Dynamic?

There are two ways to associate a unique IP address to a specific computer. One way is for the administrator to assign a number, which stays the same unless somebody decides to change it some day. That number is then a static IP address.

The other way is to assign a group of addresses to a server, and let the server hand them out as needed to any system that wants to communicate on the network. This produces a dynamic IP address. It is sometimes important to know which method is in use on a network, because with dynamic addressing, the IP address of a machine may be different each time you try to communicate with it.

Computer Names

The example address 192.168.42.122 is only one digit longer than a phone number with area code, but that’s plenty long enough to give most of us a hard time. It’s much easier for people to remember a name instead of a number, and for this reason computers in a network are also given a unique name. It may be something mundane like Sales14, but at least it’s a name and not a number.

This is not only easier to remember, but it solves the problem of a dynamic address that changes all the time, because the computer name doesn’t normally change. It does create another problem though, because the computers use only the addresses and not the names to keep track of each other. Fortunately there is a part of the TCP/IP protocol called address resolution, and it matches up the names and addresses so things keep rolling smoothly along.

Security

The problem with connecting computers to the Internet is that they are then sharing a network with many other computers from all over the world, and the users of some of those other computers are not such nice folks. Protecting the network and the information on it is one of the most important parts of a network administrator’s job.

Encryption

One way to protect information is to scramble it so that it appears to be gibberish unless someone has the right ‘key’ to unscramble it. Scrambling it is called encryption, and unscrambling it is called decryption. There are many ways to encrypt information, and of course just as many keys to decrypt it.

Encrypting and decrypting information slows things down a bit, so a decision must be made about when to use it. For packets going around the LAN, it depends on how likely it is that someone will gain unauthorized access to the LAN, called hacking. It also depends on how much damage would be done if that happened. If the threat is severe, encryption can be done not only on the transmitted packets but also to information stored on the disk drive.

For information going over the Internet, encryption is much more important unless it’s all right for the whole world to see the information. If you send your credit card number to a vendor, you must trust that vendor to encrypt and safeguard the information.

Virus Software

A computer virus is a little program that makes copies of itself to send to other computers. It’s very similar in some ways to contagious germs spreading a disease from one person to the next. And like diseases, some of these computer viruses have some really nasty side effects, like wiping out important files in the operating system or filling up the hard drive with garbage data.

As we will discuss a little later, there are ways to keep these virus programs from getting to your computer, but they are not foolproof. A lot of viruses come in attached to e-mail, and then they will mail copies of themselves to everyone in your e-mail address folder. You can’t completely block them without blocking e-mail, and most of us like to get e-mail from our friends and coworkers.

The most important prevention for viruses is to have a good anti-virus program installed on your computer. Norton, McCaffey and Panda are probably the most popular. The next most important thing is to keep the anti-virus software up-to-date, because the delinquents who write virus software are always coming up with new tricks, and the anti-virus companies are just as quickly coming up with new versions to stop them.

Access Control

If you have ever had a computer that was connected to a local area network, you almost certainly had to type in a user name and password to get network access. It’s two forms of ID, just like when you cash a check at department store.

The network administrator used that identification information to determine what you could and couldn’t do on the network. And there may have been additional passwords to access the company’ customer database, employee payroll records, or files stored on someone else’s computer.

Here are a few tips about passwords:

First, if you share files on your computer, use password protection for them even if they are available to everyone in the network. That way they can’t be tampered with if a hacker breaks in.

In choosing a password, never use your name, your birthday or other obvious personal information. The best is a random combination of letters and numbers.

Commit the password to memory, and if you must write it down, hide it. A password written on a post-it note stuck to your monitor is probably worse than no password at all.

Don’t give your password to someone you don’t know personally just because they claim to be tech support, the phone company, the police or your long-lost Aunt Matilda. Refer them to the network administrator, or better yet, get their phone number and have the network administrator call them back.

Firewalls

In a building, a firewall is a wall to keep fire from spreading from one area to another. In a computer network, a firewall is a boundary that can block unwanted data packets. The firewall may be program running on the server or router, or it may be a separate piece of hardware or even a complete computer system just for that purpose. In any case, its purpose is to look at all of the packets coming through, and decide which ones can pass and which ones get blocked.

Ports – Several pages ago, we defined a port as the place in a hub that a cable plugs into. There is another completely different kind of thing called a port, and that is a location in a computer’s memory that is used by a device or application to send and receive data. Each application will have one (or more) of these locations for its own use.

For instance, there is a common e-mail program that has port # 110, which means that the program exchanges information with the rest of the system at memory location 110. The popular game called Doom uses port # 666.

When a packet is sent over a network, it will contain not only the destination address, but also the port number of the application that will use it at that destination. One of the ways a firewall controls the packets is by looking at the port number, and only passing packets with ports that are appropriate for the destination. If nobody should be playing Doom on the network’s computers, then it would make sense to block port 666.

Another way a firewall can control traffic is to look at the source of the packet. It can have a ‘prohibited’ list that keeps out packets from certain IP addresses, or it can have an ‘allowed’ list and block everyone who isn’t on it. Ports can be done the same way, with a ‘prohibited’ or ‘allowed’ list of ports.

Conclusion

There is much more to know about security, and about networks in general, if one is to be involved in managing them. The purpose of this paper is to present just enough information to enable you talk with network administrators and to understand their concerns when presenting network products to them. For additional training in this subject, we recommend the Micro2000 A+ and Network+ courses.

:: Basic Networking Tutorial ::

2008-11-23T18:57:00.000-08:00

What is a Computer Network?

A network is any collection of independent computers that communicate with one another over a shared network medium.A computer network is a collection of two or more connected computers. When these computers are joined in a network, people can share files and peripherals such as modems, printers, tape backup drives, or CD-ROM drives. When networks at multiple locations are connected using services available from phone companies, people can send e-mail, share links to the global Internet, or conduct videoconferences in real time with other remote users. As companies rely on applications like electronic mail and database management for core business operations, computer networking becomes increasingly more important.

Every network includes:

At least two computers Server or Client workstation.
Networking Interface Card’s (NIC)
A connection medium, usually a wire or cable, although wireless communication between networked computers and peripherals is also possible.
Network Operating system software, such as Microsoft Windows NT or 2000, Novell NetWare, Unix and Linux.

Types of Networks:

LANs (Local Area Networks)

A network is any collection of independent computers that communicate with one another over a shared network medium. LANs are networks usually confined to a geographic area, such as a single building or a college campus. LANs can be small, linking as few as three computers, but often link hundreds of computers used by thousands of people. The development of standard networking protocols and media has resulted in worldwide proliferation of LANs throughout business and educational organizations.

WANs (Wide Area Networks)

Wide area networking combines multiple LANs that are geographically separate. This is accomplished by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines (both synchronous and asynchronous), satellite links, and data packet carrier services. Wide area networking can be as simple as a modem and remote access server for employees to dial into, or it can be as complex as hundreds of branch offices globally linked using special routing protocols and filters to minimize the expense of sending data sent over vast distances.

Internet

The Internet is a system of linked networks that are worldwide in scope and facilitate data communication services such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups.

With the meteoric rise in demand for connectivity, the Internet has become a communications highway for millions of users. The Internet was initially restricted to military and academic institutions, but now it is a full-fledged conduit for any and all forms of information and commerce. Internet websites now provide personal, educational, political and economic resources to every corner of the planet.

Intranet

With the advancements made in browser-based software for the Internet, many private organizations are implementing intranets. An intranet is a private network utilizing Internet-type tools, but available only within that organization. For large organizations, an intranet provides an easy access mode to corporate information for employees.

MANs (Metropolitan area Networks)

The refers to a network of computers with in a City.

VPN (Virtual Private Network)

VPN uses a technique known as tunneling to transfer data securely on the Internet to a remote access server on your workplace network. Using a VPN helps you save money by using the public Internet instead of making long–distance phone calls to connect securely with your private network. There are two ways to create a VPN connection, by dialing an Internet service provider (ISP), or connecting directly to Internet.

Categories of Network:

Network can be divided in to two main categories:

Peer-to-peer.
Server – based.

In peer-to-peer networking there are no dedicated servers or hierarchy among the computers. All of the computers are equal and therefore known as peers. Normally each computer serves as Client/Server and there is no one assigned to be an administrator responsible for the entire network.

Peer-to-peer networks are good choices for needs of small organizations where the users are allocated in the same general area, security is not an issue and the organization and the network will have limited growth within the foreseeable future.

The term Client/server refers to the concept of sharing the work involved in processing data between the client computer and the most powerful server computer.

The client/server network is the most efficient way to provide:

Databases and management of applications such as Spreadsheets, Accounting, Communications and Document management.
Network management.
Centralized file storage.

The client/server model is basically an implementation of distributed or cooperative processing. At the heart of the model is the concept of splitting application functions between a client and a server processor. The division of labor between the different processors enables the application designer to place an application function on the processor that is most appropriate for that function. This lets the software designer optimize the use of processors--providing the greatest possible return on investment for the hardware.

Client/server application design also lets the application provider mask the actual location of application function. The user often does not know where a specific operation is executing. The entire function may execute in either the PC or server, or the function may be split between them. This masking of application function locations enables system implementers to upgrade portions of a system over time with a minimum disruption of application operations, while protecting the investment in existing hardware and software.

The OSI Model:

Open System Interconnection (OSI) reference model has become an International standard and serves as a guide for networking. This model is the best known and most widely used guide to describe networking environments. Vendors design network products based on the specifications of the OSI model. It provides a description of how network hardware and software work together in a layered fashion to make communications possible. It also helps with trouble shooting by providing a frame of reference that describes how components are supposed to function.

There are seven to get familiar with and these are the physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and the application layer.

Physical Layer, is just that the physical parts of the network such as wires, cables, and there media along with the length. Also this layer takes note of the electrical signals that transmit data throughout system.
Data Link Layer, this layer is where we actually assign meaning to the electrical signals in the network. The layer also determines the size and format of data sent to printers, and other devices. Also I don’t want to forget that these are also called nodes in the network. Another thing to consider in this layer is will also allow and define the error detection and correction schemes that insure data was sent and received.
Network Layer, this layer provides the definition for the connection of two dissimilar networks.
Transport Layer, this layer allows data to be broken into smaller packages for data to be distributed and addressed to other nodes (workstations).
Session Layer, this layer helps out with the task to carry information from one node (workstation) to another node (workstation). A session has to be made before we can transport information to another computer.
Presentation Layer, this layer is responsible to code and decode data sent to the node.
Application Layer, this layer allows you to use an application that will communicate with say the operation system of a server. A good example would be using your web browser to interact with the operating system on a server such as Windows NT, which in turn gets the data you requested.

Network Architectures:

Ethernet

Ethernet is the most popular physical layer LAN technology in use today. Other LAN types include Token Ring, Fast Ethernet, Fiber Distributed Data Interface (FDDI), Asynchronous Transfer Mode (ATM) and LocalTalk. Ethernet is popular because it strikes a good balance between speed, cost and ease of installation. These benefits, combined with wide acceptance in the computer marketplace and the ability to support virtually all popular network protocols, make Ethernet an ideal networking technology for most computer users today. The Institute for Electrical and Electronic Engineers (IEEE) defines the Ethernet standard as IEEE Standard 802.3. This standard defines rules for configuring an Ethernet network as well as specifying how elements in an Ethernet network interact with one another. By adhering to the IEEE standard, network equipment and network protocols can communicate efficiently.

Fast Ethernet

For Ethernet networks that need higher transmission speeds, the Fast Ethernet standard (IEEE 802.3u) has been established. This standard raises the Ethernet speed limit from 10 Megabits per second (Mbps) to 100 Mbps with only minimal changes to the existing cable structure. There are three types of Fast Ethernet: 100BASE-TX for use with level 5 UTP cable, 100BASE-FX for use with fiber-optic cable, and 100BASE-T4 which utilizes an extra two wires for use with level 3 UTP cable. The 100BASE-TX standard has become the most popular due to its close compatibility with the 10BASE-T Ethernet standard. For the network manager, the incorporation of Fast Ethernet into an existing configuration presents a host of decisions. Managers must determine the number of users in each site on the network that need the higher throughput, decide which segments of the backbone need to be reconfigured specifically for 100BASE-T and then choose the necessary hardware to connect the 100BASE-T segments with existing 10BASE-T segments. Gigabit Ethernet is a future technology that promises a migration path beyond Fast Ethernet so the next generation of networks will support even higher data transfer speeds.

Token Ring

Token Ring is another form of network configuration which differs from Ethernet in that all messages are transferred in a unidirectional manner along the ring at all times. Data is transmitted in tokens, which are passed along the ring and viewed by each device. When a device sees a message addressed to it, that device copies the message and then marks that message as being read. As the message makes its way along the ring, it eventually gets back to the sender who now notes that the message was received by the intended device. The sender can then remove the message and free that token for use by others.

Various PC vendors have been proponents of Token Ring networks at different times and thus these types of networks have been implemented in many organizations.

FDDI

FDDI (Fiber-Distributed Data Interface) is a standard for data transmission on fiber optic lines in a local area network that can extend in range up to 200 km (124 miles). The FDDI protocol is based on the token ring protocol. In addition to being large geographically, an FDDI local area network can support thousands of users.

Protocols:

Network protocols are standards that allow computers to communicate. A protocol defines how computers identify one another on a network, the form that the data should take in transit, and how this information is processed once it reaches its final destination. Protocols also define procedures for handling lost or damaged transmissions or "packets." TCP/IP (for UNIX, Windows NT, Windows 95 and other platforms), IPX (for Novell NetWare), DECnet (for networking Digital Equipment Corp. computers), AppleTalk (for Macintosh computers), and NetBIOS/NetBEUI (for LAN Manager and Windows NT networks) are the main types of network protocols in use today.

Although each network protocol is different, they all share the same physical cabling. This common method of accessing the physical network allows multiple protocols to peacefully coexist over the network media, and allows the builder of a network to use common hardware for a variety of protocols. This concept is known as "protocol independence,"

Some Important Protocols and their job:

Protocol	Acronym	Its Job
Point-To-Point	TCP/IP	The backbone protocol of the internet. Popular also for intranets using the internet
Transmission Control Protocol/internet Protocol	TCP/IP	The backbone protocol of the internet. Popular also for intranets using the internet
Internetwork Package Exchange/Sequenced Packet Exchange	IPX/SPX	This is a standard protocol for Novell Network Operating System
NetBIOS Extended User Interface	NetBEUI	This is a Microsoft protocol that doesn’t support routing to other networks
File Transfer Protocol	FTP	Used to send and receive files from a remote host
Hyper Transfer Protocol	HTTP	Used for the web to send documents that are encoded in HTML.
Network File Services	NFS	Allows network nodes or workstations to access files and drives as if they were their own.
Simple Mail Transfer Protocol	SMTP	Used to send Email over a network
Telnet		Used to connect to a host and emulate a terminal that the remote server can recognize

Introduction to TCP/IP Networks:

TCP/IP-based networks play an increasingly important role in computer networks. Perhaps one reason for their appeal is that they are based on an open specification that is not controlled by any vendor.

What Is TCP/IP?

TCP stands for Transmission Control Protocol and IP stands for Internet Protocol. The term TCP/IP is not limited just to these two protocols, however. Frequently, the term TCP/IP is used to refer to a group of protocols related to the TCP and IP protocols such as the User Datagram Protocol (UDP), File Transfer Protocol (FTP), Terminal Emulation Protocol (TELNET), and so on.

The Origins of TCP/IP

In the late 1960s, DARPA (the Defense Advanced Research Project Agency), in the United States, noticed that there was a rapid proliferation of computers in military communications. Computers, because they can be easily programmed, provide flexibility in achieving network functions that is not available with other types of communications equipment. The computers then used in military communications were manufactured by different vendors and were designed to interoperate with computers from that vendor only. Vendors used proprietary protocols in their communications equipment. The military had a multi vendor network but no common protocol to support the heterogeneous equipment from different vendors

Net work Cables and Stuff:

In the network you will commonly find three types of cables used these are the, coaxial cable, fiber optic and twisted pair.

Thick Coaxial Cable

This type cable is usually yellow in color and used in what is called thicknets, and has two conductors. This coax can be used in 500-meter lengths. The cable itself is made up of a solid center wire with a braided metal shield and plastic sheathing protecting the rest of the wire.

Thin Coaxial Cable

As with the thick coaxial cable is used in thicknets the thin version is used in thinnets. This type cable is also used called or referred to as RG-58. The cable is really just a cheaper version of the thick cable.

Fiber Optic Cable

As we all know fiber optics are pretty darn cool and not cheap. This cable is smaller and can carry a vast amount of information fast and over long distances.

Twisted Pair Cables

These come in two flavors of unshielded and shielded.

Unshielded Twisted Pair (UTP)

This is the most popular form of cables in the network and the cheapest form that you can go with. The UTP has four pairs of wires and all inside plastic sheathing. The biggest reason that we call it Twisted Pair is to protect the wires from interference from themselves. Each wire is only protected with a thin plastic sheath.

Shielded Twisted Pair (STP)

Is more common in high-speed networks. The biggest difference you will see in the UTP and STP is that the STP use’s metallic shield wrapping to protect the wire from interference.

-Something else to note about these cables is that they are defined in numbers also. The bigger the number the better the protection from interference. Most networks should go with no less than a CAT 3 and CAT 5 is most recommended.

-Now you know about cables we need to know about connectors. This is pretty important and you will most likely need the RJ-45 connector. This is the cousin of the phone jack connector and looks real similar with the exception that the RJ-45 is bigger. Most commonly your connector are in two flavors and this is BNC (Bayonet Naur Connector) used in thicknets and the RJ-45 used in smaller networks using UTP/STP.

Ethernet Cabling

Now to familiarize you with more on the Ethernet and it’s cabling we need to look at the 10’s. 10Base2, is considered the thin Ethernet, thinnet, and thinwire which uses light coaxial cable to create a 10 Mbps network. The cable segments in this network can’t be over 185 meters in length. These cables connect with the BNC connector. Also as a note these unused connection must have a terminator, which will be a 50-ohm terminator.

10Base5, this is considered a thicknet and is used with coaxial cable arrangement such as the BNC connector. The good side to the coaxial cable is the high-speed transfer and cable segments can be up to 500 meters between nodes/workstations. You will typically see the same speed as the 10Base2 but larger cable lengths for more versatility.

10BaseT, the “T” stands for twisted as in UTP (Unshielded Twisted Pair) and uses this for 10Mbps of transfer. The down side to this is you can only have cable lengths of 100 meters between nodes/workstations. The good side to this network is they are easy to set up and cheap! This is why they are so common an ideal for small offices or homes.

100BaseT, is considered Fast Ethernet uses STP (Shielded Twisted Pair) reaching data transfer of 100Mbps. This system is a little more expensive but still remains popular as the 10BaseT and cheaper than most other type networks. This on of course would be the cheap fast version.

10BaseF, this little guy has the advantage of fiber optics and the F stands for just that. This arrangement is a little more complicated and uses special connectors and NIC’s along with hubs to create its network. Pretty darn neat and not to cheap on the wallet.

An important part of designing and installing an Ethernet is selecting the appropriate Ethernet medium. There are four major types of media in use today: Thickwire for 10BASE5 networks, thin coax for 10BASE2 networks, unshielded twisted pair (UTP) for 10BASE-T networks and fiber optic for 10BASE-FL or Fiber-Optic Inter-Repeater Link (FOIRL) networks. This wide variety of media reflects the evolution of Ethernet and also points to the technology's flexibility. Thickwire was one of the first cabling systems used in Ethernet but was expensive and difficult to use. This evolved to thin coax, which is easier to work with and less expensive.

Network Topologies:

What is a Network topology?

A network topology is the geometric arrangement of nodes and cable links in a LAN,

There are three topology’s to think about when you get into networks. These are the star, rind, and the bus.

Star, a ring topology features a logically closed loop. Data packets travel in a single direction around the ring from one network device to the next. Each network device acts as a repeater, meaning it regenerates the signal

Ring, in a star topology each node has a dedicated set of wires connecting it to a central network hub. Since all traffic passes through the hub, the hub becomes a central point for isolating network problems and gathering network statistics.

Bus, the bus topology, each node (computer, server, peripheral etc.) attaches directly to a common cable. This topology most often serves as the backbone for a network. In some instances, such as in classrooms or labs, a bus will connect small workgroups

Collisions:

Ethernet is a shared media, so there are rules for sending packets of data to avoid conflicts and protect data integrity. Nodes determine when the network is available for sending packets. It is possible that two nodes at different locations attempt to send data at the same time. When both PCs are transferring a packet to the network at the same time, a collision will result.

Minimizing collisions is a crucial element in the design and operation of networks. Increased collisions are often the result of too many users on the network, which results in a lot of contention for network bandwidth. This can slow the performance of the network from the user's point of view. Segmenting the network, where a network is divided into different pieces joined together logically with a bridge or switch, is one way of reducing an overcrowded network.

Ethernet Products:

The standards and technology that have just been discussed help define the specific products that network managers use to build Ethernet networks. The following text discusses the key products needed to build an Ethernet LAN.

Transceivers

Transceivers are used to connect nodes to the various Ethernet media. Most computers and network interface cards contain a built-in 10BASE-T or 10BASE2 transceiver, allowing them to be connected directly to Ethernet without requiring an external transceiver. Many Ethernet devices provide an AUI connector to allow the user to connect to any media type via an external transceiver. The AUI connector consists of a 15-pin D-shell type connector, female on the computer side, male on the transceiver side. Thickwire (10BASE5) cables also use transceivers to allow connections.

For Fast Ethernet networks, a new interface called the MII (Media Independent Interface) was developed to offer a flexible way to support 100 Mbps connections. The MII is a popular way to connect 100BASE-FX links to copper-based Fast Ethernet devices.

Network Interface Cards:

Network interface cards, commonly referred to as NICs, and are used to connect a PC to a network. The NIC provides a physical connection between the networking cable and the computer's internal bus. Different computers have different bus architectures; PCI bus master slots are most commonly found on 486/Pentium PCs and ISA expansion slots are commonly found on 386 and older PCs. NICs come in three basic varieties: 8-bit, 16-bit, and 32-bit. The larger the number of bits that can be transferred to the NIC, the faster the NIC can transfer data to the network cable.

Many NIC adapters comply with Plug-n-Play specifications. On these systems, NICs are automatically configured without user intervention, while on non-Plug-n-Play systems, configuration is done manually through a setup program and/or DIP switches.

Cards are available to support almost all networking standards, including the latest Fast Ethernet environment. Fast Ethernet NICs are often 10/100 capable, and will automatically set to the appropriate speed. Full duplex networking is another option, where a dedicated connection to a switch allows a NIC to operate at twice the speed.

Hubs/Repeaters:

Hubs/repeaters are used to connect together two or more Ethernet segments of any media type. In larger designs, signal quality begins to deteriorate as segments exceed their maximum length. Hubs provide the signal amplification required to allow a segment to be extended a greater distance. A hub takes any incoming signal and repeats it out all ports.

Ethernet hubs are necessary in star topologies such as 10BASE-T. A multi-port twisted pair hub allows several point-to-point segments to be joined into one network. One end of the point-to-point link is attached to the hub and the other is attached to the computer. If the hub is attached to a backbone, then all computers at the end of the twisted pair segments can communicate with all the hosts on the backbone. The number and type of hubs in any one-collision domain is limited by the Ethernet rules. These repeater rules are discussed in more detail later.

Network Type	Max Nodes Per Segment	Max Distance Per Segment
10BASE-T 10BASE2 10BASE5 10BASE-FL	2 30 100 2	100m 185m 500m 2000m

Adding Speed:

While repeaters allow LANs to extend beyond normal distance limitations, they still limit the number of nodes that can be supported. Bridges and switches, however, allow LANs to grow significantly larger by virtue of their ability to support full Ethernet segments on each port. Additionally, bridges and switches selectively filter network traffic to only those packets needed on each segment - this significantly increases throughput on each segment and on the overall network. By providing better performance and more flexibility for network topologies, bridges and switches will continue to gain popularity among network managers.

Bridges:

The function of a bridge is to connect separate networks together. Bridges connect different networks types (such as Ethernet and Fast Ethernet) or networks of the same type. Bridges map the Ethernet addresses of the nodes residing on each network segment and allow only necessary traffic to pass through the bridge. When a packet is received by the bridge, the bridge determines the destination and source segments. If the segments are the same, the packet is dropped ("filtered"); if the segments are different, then the packet is "forwarded" to the correct segment. Additionally, bridges do not forward bad or misaligned packets.

Bridges are also called "store-and-forward" devices because they look at the whole Ethernet packet before making filtering or forwarding decisions. Filtering packets, and regenerating forwarded packets enable bridging technology to split a network into separate collision domains. This allows for greater distances and more repeaters to be used in the total network design.

Ethernet Switches:

Ethernet switches are an expansion of the concept in Ethernet bridging. LAN switches can link four, six, ten or more networks together, and have two basic architectures: cut-through and store-and-forward. In the past, cut-through switches were faster because they examined the packet destination address only before forwarding it on to its destination segment. A store-and-forward switch, on the other hand, accepts and analyzes the entire packet before forwarding it to its destination.

It takes more time to examine the entire packet, but it allows the switch to catch certain packet errors and keep them from propagating through the network. Both cut-through and store-and-forward switches separate a network into collision domains, allowing network design rules to be extended. Each of the segments attached to an Ethernet switch has a full 10 Mbps of bandwidth shared by fewer users, which results in better performance (as opposed to hubs that only allow bandwidth sharing from a single Ethernet). Newer switches today offer high-speed links, FDDI, Fast Ethernet or ATM. These are used to link switches together or give added bandwidth to high-traffic servers. A network composed of a number of switches linked together via uplinks is termed a "collapsed backbone" network.

Routers:

Routers filter out network traffic by specific protocol rather than by packet address. Routers also divide networks logically instead of physically. An IP router can divide a network into various subnets so that only traffic destined for particular IP addresses can pass between segments. Network speed often decreases due to this type of intelligent forwarding. Such filtering takes more time than that exercised in a switch or bridge, which only looks at the Ethernet address. However, in more complex networks, overall efficiency is improved by using routers.

What is a network firewall?

A firewall is a system or group of systems that enforces an access control policy between two networks. The actual means by which this is accomplished varies widely, but in principle, the firewall can be thought of as a pair of mechanisms: one which exists to block traffic, and the other which exists to permit traffic. Some firewalls place a greater emphasis on blocking traffic, while others emphasize permitting traffic. Probably the most important thing to recognize about a firewall is that it implements an access control policy. If you don't have a good idea of what kind of access you want to allow or to deny, a firewall really won't help you. It's also important to recognize that the firewall's configuration, because it is a mechanism for enforcing policy, imposes its policy on everything behind it. Administrators for firewalls managing the connectivity for a large number of hosts therefore have a heavy responsibility.

Network Design Criteria:

Ethernets and Fast Ethernets have design rules that must be followed in order to function correctly. Maximum number of nodes, number of repeaters and maximum segment distances are defined by the electrical and mechanical design properties of each type of Ethernet and Fast Ethernet media.

A network using repeaters, for instance, functions with the timing constraints of Ethernet. Although electrical signals on the Ethernet media travel near the speed of light, it still takes a finite time for the signal to travel from one end of a large Ethernet to another. The Ethernet standard assumes it will take roughly 50 microseconds for a signal to reach its destination.

Ethernet is subject to the "5-4-3" rule of repeater placement: the network can only have five segments connected; it can only use four repeaters; and of the five segments, only three can have users attached to them; the other two must be inter-repeater links.

If the design of the network violates these repeater and placement rules, then timing guidelines will not be met and the sending station will resend that packet. This can lead to lost packets and excessive resent packets, which can slow network performance and create trouble for applications. Fast Ethernet has modified repeater rules, since the minimum packet size takes less time to transmit than regular Ethernet. The length of the network links allows for a fewer number of repeaters. In Fast Ethernet networks, there are two classes of repeaters. Class I repeaters have a latency of 0.7 microseconds or less and are limited to one repeater per network. Class II repeaters have a latency of 0.46 microseconds or less and are limited to two repeaters per network. The following are the distance (diameter) characteristics for these types of Fast Ethernet repeater combinations:

Fast Ethernet	Copper	Fiber
No Repeaters One Class I Repeater One Class II Repeater Two Class II Repeaters	100m 200m 200m 205m	412m* 272m 272m 228m

* Full Duplex Mode 2 km

When conditions require greater distances or an increase in the number of nodes/repeaters, then a bridge, router or switch can be used to connect multiple networks together. These devices join two or more separate networks, allowing network design criteria to be restored. Switches allow network designers to build large networks that function well. The reduction in costs of bridges and switches reduces the impact of repeater rules on network design.

Each network connected via one of these devices is referred to as a separate collision domain in the overall network.

Types of Servers:

Device Servers

A device server is defined as a specialized, network-based hardware device designed to perform a single or specialized set of server functions. It is characterized by a minimal operating architecture that requires no per seat network operating system license, and client access that is independent of any operating system or proprietary protocol. In addition the device server is a "closed box," delivering extreme ease of installation, minimal maintenance, and can be managed by the client remotely via a Web browser.

Print servers, terminal servers, remote access servers and network time servers are examples of device servers which are specialized for particular functions. Each of these types of servers has unique configuration attributes in hardware or software that help them to perform best in their particular arena.

Print Servers

Print servers allow printers to be shared by other users on the network. Supporting either parallel and/or serial interfaces, a print server accepts print jobs from any person on the network using supported protocols and manages those jobs on each appropriate printer.

Print servers generally do not contain a large amount of memory; printers simply store information in a queue. When the desired printer becomes available, they allow the host to transmit the data to the appropriate printer port on the server. The print server can then simply queue and print each job in the order in which print requests are received, regardless of protocol used or the size of the job.

Multiport Device Servers

Devices that are attached to a network through a multiport device server can be shared between terminals and hosts at both the local site and throughout the network. A single terminal may be connected to several hosts at the same time (in multiple concurrent sessions), and can switch between them. Multiport device servers are also used to network devices that have only serial outputs. A connection between serial ports on different servers is opened, allowing data to move between the two devices.

Given its natural translation ability, a multi-protocol multiport device server can perform conversions between the protocols it knows, like LAT and TCP/IP. While server bandwidth is not adequate for large file transfers, it can easily handle host-to-host inquiry/response applications, electronic mailbox checking, etc. And it is far more economical than the alternatives of acquiring expensive host software and special-purpose converters. Multiport device and print servers give their users greater flexibility in configuring and managing their networks.

Whether it is moving printers and other peripherals from one network to another, expanding the dimensions of interoperability or preparing for growth, multiport device servers can fulfill your needs, all without major rewiring.

Access Servers

While Ethernet is limited to a geographic area, remote users such as traveling sales people need access to network-based resources. Remote LAN access, or remote access, is a popular way to provide this connectivity. Access servers use telephone services to link a user or office with an office network. Dial-up remote access solutions such as ISDN or asynchronous dial introduce more flexibility. Dial-up remote access offers both the remote office and the remote user the economy and flexibility of "pay as you go" telephone services. ISDN is a special telephone service that offers three channels, two 64 Kbps "B" channels for user data and a "D" channel for setting up the connection. With ISDN, the B channels can be combined for double bandwidth or separated for different applications or users. With asynchronous remote access, regular telephone lines are combined with modems and remote access servers to allow users and networks to dial anywhere in the world and have data access. Remote access servers provide connection points for both dial-in and dial-out applications on the network to which they are attached. These hybrid devices route and filter protocols and offer other services such as modem pooling and terminal/printer services. For the remote PC user, one can connect from any available telephone jack (RJ45), including those in a hotel rooms or on most airplanes.

Network Time Servers

A network time server is a server specialized in the handling of timing information from sources such as satellites or radio broadcasts and is capable of providing this timing data to its attached network. Specialized protocols such as NTP or udp/time allow a time server to communicate to other network nodes ensuring that activities that must be coordinated according to their time of execution are synchronized correctly. GPS satellites are one source of information that can allow global installations to achieve constant timing.

IP Addressing:

An IP (Internet Protocol) address is a unique identifier for a node or host connection on an IP network. An IP address is a 32 bit binary number usually represented as 4 decimal values, each representing 8 bits, in the range 0 to 255 (known as octets) separated by decimal points. This is known as "dotted decimal" notation.

Example: 140.179.220.200

It is sometimes useful to view the values in their binary form.

140 .179 .220 .200

10001100.10110011.11011100.11001000

Every IP address consists of two parts, one identifying the network and one identifying the node. The Class of the address and the subnet mask determine which part belongs to the network address and which part belongs to the node address.

Address Classes:

There are 5 different address classes. You can determine which class any IP address is in by examining the first 4 bits of the IP address.

Class A addresses begin with 0xxx, or 1 to 126 decimal.

Class B addresses begin with 10xx, or 128 to 191 decimal.

Class C addresses begin with 110x, or 192 to 223 decimal.

Class D addresses begin with 1110, or 224 to 239 decimal.

Class E addresses begin with 1111, or 240 to 254 decimal.

Addresses beginning with 01111111, or 127 decimal, are reserved for loopback and for internal testing on a local machine. [You can test this: you should always be able to ping 127.0.0.1, which points to yourself] Class D addresses are reserved for multicasting. Class E addresses are reserved for future use. They should not be used for host addresses.

Now we can see how the Class determines, by default, which part of the IP address belongs to the network (N) and which part belongs to the node (n).

Class A -- NNNNNNNN.nnnnnnnn.nnnnnnn.nnnnnnn

Class B -- NNNNNNNN.NNNNNNNN.nnnnnnnn.nnnnnnnn

Class C -- NNNNNNNN.NNNNNNNN.NNNNNNNN.nnnnnnnn

In the example, 140.179.220.200 is a Class B address so by default the Network part of the address (also known as the Network Address) is defined by the first two octets (140.179.x.x) and the node part is defined by the last 2 octets (x.x.220.200).

In order to specify the network address for a given IP address, the node section is set to all "0"s. In our example, 140.179.0.0 specifies the network address for 140.179.220.200. When the node section is set to all "1"s, it specifies a broadcast that is sent to all hosts on the network. 140.179.255.255 specifies the example broadcast address. Note that this is true regardless of the length of the node section.

Private Subnets:

There are three IP network addresses reserved for private networks. The addresses are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. They can be used by anyone setting up internal IP networks, such as a lab or home LAN behind a NAT or proxy server or a router. It is always safe to use these because routers on the Internet will never forward packets coming from these addresses

Subnetting an IP Network can be done for a variety of reasons, including organization, use of different physical media (such as Ethernet, FDDI, WAN, etc.), preservation of address space, and security. The most common reason is to control network traffic. In an Ethernet network, all nodes on a segment see all the packets transmitted by all the other nodes on that segment. Performance can be adversely affected under heavy traffic loads, due to collisions and the resulting retransmissions. A router is used to connect IP networks to minimize the amount of traffic each segment must receive.

Subnet Masking

Applying a subnet mask to an IP address allows you to identify the network and node parts of the address. The network bits are represented by the 1s in the mask, and the node bits are represented by the 0s. Performing a bitwise logical AND operation between the IP address and the subnet mask results in the Network Address or Number.

For example, using our test IP address and the default Class B subnet mask, we get:

10001100.10110011.11110000.11001000 140.179.240.200 Class B IP Address

11111111.11111111.00000000.00000000 255.255.000.000 Default Class B Subnet Mask

10001100.10110011.00000000.00000000 140.179.000.000 Network Address

Default subnet masks:

Class A - 255.0.0.0 - 11111111.00000000.00000000.00000000

Class B - 255.255.0.0 - 11111111.11111111.00000000.00000000

Class C - 255.255.255.0 - 11111111.11111111.11111111.00000000

CIDR -- Classless InterDomain Routing.

CIDR was invented several years ago to keep the internet from running out of IP addresses. The "classful" system of allocating IP addresses can be very wasteful; anyone who could reasonably show a need for more that 254 host addresses was given a Class B address block of 65533 host addresses. Even more wasteful were companies and organizations that were allocated Class A address blocks, which contain over 16 Million host addresses! Only a tiny percentage of the allocated Class A and Class B address space has ever been actually assigned to a host computer on the Internet.

People realized that addresses could be conserved if the class system was eliminated. By accurately allocating only the amount of address space that was actually needed, the address space crisis could be avoided for many years. This was first proposed in 1992 as a scheme called Supernetting.

The use of a CIDR notated address is the same as for a Classful address. Classful addresses can easily be written in CIDR notation (Class A = /8, Class B = /16, and Class C = /24)

It is currently almost impossible for an individual or company to be allocated their own IP address blocks. You will simply be told to get them from your ISP. The reason for this is the ever-growing size of the internet routing table. Just 5 years ago, there were less than 5000 network routes in the entire Internet. Today, there are over 90,000. Using CIDR, the biggest ISPs are allocated large chunks of address space (usually with a subnet mask of /19 or even smaller); the ISP's customers (often other, smaller ISPs) are then allocated networks from the big ISP's pool. That way, all the big ISP's customers (and their customers, and so on) are accessible via 1 network route on the Internet.

It is expected that CIDR will keep the Internet happily in IP addresses for the next few years at least. After that, IPv6, with 128 bit addresses, will be needed. Under IPv6, even sloppy address allocation would comfortably allow a billion unique IP addresses for every person on earth

Examining your network with commands:

Ping

PING is used to check for a response from another computer on the network. It can tell you a great deal of information about the status of the network and the computers you are communicating with.

Ping returns different responses depending on the computer in question. The responses are similar depending on the options used.

Ping uses IP to request a response from the host. It does not use TCP

.It takes its name from a submarine sonar search - you send a short sound burst and listen for an echo - a ping - coming back.

In an IP network, `ping' sends a short data burst - a single packet - and listens for a single packet in reply. Since this tests the most basic function of an IP network (delivery of single packet), it's easy to see how you can learn a lot from some `pings'.

To stop ping, type control-c. This terminates the program and prints out a nice summary of the number of packets transmitted, the number received, and the percentage of packets lost, plus the minimum, average, and maximum round-trip times of the packets.

Sample ping session

PING localhost (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=1 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=3 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=4 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=5 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=6 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=7 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=8 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=9 ttl=255 time=2 ms

localhost ping statistics

10 packets transmitted, 10 packets received, 0% packet loss
round-trip min/avg/max = 2/2/2 ms
meikro$

The Time To Live (TTL) field can be interesting. The main purpose of this is so that a packet doesn't live forever on the network and will eventually die when it is deemed "lost." But for us, it provides additional information. We can use the TTL to determine approximately how many router hops the packet has gone through. In this case it's 255 minus N hops, where N is the TTL of the returning Echo Replies. If the TTL field varies in successive pings, it could indicate that the successive reply packets are going via different routes, which isn't a great thing.

The time field is an indication of the round-trip time to get a packet to the remote host. The reply is measured in milliseconds. In general, it's best if round-trip times are under 200 milliseconds. The time it takes a packet to reach its destination is called latency. If you see a large variance in the round-trip times (which is called "jitter"), you are going to see poor performance talking to the host

NSLOOKUP

NSLOOKUP is an application that facilitates looking up hostnames on the network. It can reveal the IP address of a host or, using the IP address, return the host name.

It is very important when troubleshooting problems on a network that you can verify the components of the networking process. Nslookup allows this by revealing details within the infrastructure.

NETSTAT

NETSTAT is used to look up the various active connections within a computer. It is helpful to understand what computers or networks you are connected to. This allows you to further investigate problems. One host may be responding well but another may be less responsive.

IPconfig

This is a Microsoft windows NT, 2000 command. It is very useful in determining what could be wrong with a network.

This command when used with the /all switch, reveal enormous amounts of troubleshooting information within the system.

Windows 2000 IP Configuration

Host Name . . . . . . . . . . . . : cowder
Primary DNS Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Broadcast
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . :
WAN (PPP/SLIP) Interface
Physical Address. . . . . . . . . : 00-53-45-00-00-00
DHCP Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : 12.90.108.123
Subnet Mask . . . . . . . . . . . : 255.255.255.255
Default Gateway . . . . . . . . . : 12.90.108.125
DNS Servers . . . . . . . . . . . : 12.102.244.2
204.127.129.2

Traceroute

Traceroute on Unix and Linux (or tracert in the Microsoft world) attempts to trace the current network path to a destination. Here is an example of a traceroute run to www.berkeley.edu:

$ traceroute www.berkeley.edu

traceroute to amber.Berkeley.EDU (128.32.25.12), 30 hops max, 40 byte packets

1 sf1-e3.wired.net (206.221.193.1) 3.135 ms 3.021 ms 3.616 ms

2 sf0-e2s2.wired.net (205.227.206.33) 1.829 ms 3.886 ms 2.772 ms

3 paloalto-cr10.bbnplanet.net (131.119.26.105) 5.327 ms 4.597 ms 5.729 ms

4 paloalto-br1.bbnplanet.net (131.119.0.193) 4.842 ms 4.615 ms 3.425 ms

5 sl-sj-2.sprintlink.net (4.0.1.66) 7.488 ms 38.804 ms 7.708 ms

6 144.232.8.81 (144.232.8.81) 6.560 ms 6.631 ms 6.565 ms

7 144.232.4.97 (144.232.4.97) 7.638 ms 7.948 ms 8.129 ms

8 144.228.146.50 (144.228.146.50) 9.504 ms 12.684 ms 16.648 ms

9 f5-0.inr-666-eva.berkeley.edu (198.128.16.21) 9.762 ms 10.611 ms 10.403 ms

10 f0-0.inr-107-eva.Berkeley.EDU (128.32.2.1) 11.478 ms 10.868 ms 9.367 ms

11 f8-0.inr-100-eva.Berkeley.EDU (128.32.235.100) 10.738 ms 11.693 ms 12.520 ms

Introduction to Client Server Networks

2008-11-23T18:54:00.000-08:00

By Bradley Mitchell, About.com

The term client-server refers to a popular model for computer networking that utilizes client and server devices each designed for specific purposes. The client-server model can be used on the Internet as well as local area networks (LANs). Examples of client-server systems on the Internet include Web browsers and Web servers, FTP clients and servers, and DNS.

Client and Server Devices

Client/server networking grew in popularity many years ago as personal computers (PCs) became the common alternative to older mainframe computers. Client devices are typically PCs with network software applications installed that request and receive information over the network. Mobile devices as well as desktop computers can both function as clients.

A server device typically stores files and databases including more complex applications like Web sites. Server devices often feature higher-powered central processors, more memory, and larger disk drives than clients.

Client-Server Applications

The client-server model distinguishes between applications as well as devices. Network clients make requests to a server by sending messages, and servers respond to their clients by acting on each request and returning results. One server generally supports numerous clients, and multiple servers can be networked together in a pool to handle the increased processing load as the number of clients grows.

A client computer and a server computer are usually two separate devices, each customized for their designed purpose. For example, a Web client works best with a large screen display, while a Web server does not need any display at all and can be located anywhere in the world. However, in some cases a given device can function both as a client and a server for the same application. Likewise, a device that is a server for one application can simultaneously act as a client to other servers, for different applications.

[Some of the most popular applications on the Internet follow the client-server model including email, FTP and Web services. Each of these clients features a user interface (either graphic- or text-based) and a client application that allows the user to connect to servers. In the case of email and FTP, users enter a computer name (or sometimes an IP address) into the interface to set up connections to the server.

Local Client-Server Networks

Many home networks utilize client-server systems without even realizing it. Broadband routers, for example, contain DHCP servers that provide IP addresses to the home computers (DHCP clients). Other types of network servers found in home include print servers and backup servers.

Client-Server vs Peer-to-Peer and Other Models

The client-server model was originally developed to allow more users to share access to database applications. Compared to the mainframe approach, client-server offers improved scalability because connections can be made as needed rather than being fixed. The client-server model also supports modular applications that can make the job of creating software easier. In so-called "two-tier" and "three-tier" types of client-server systems, software applications are separated into modular pieces, and each piece is installed on clients or servers specialized for that subsystem. Client-server is just one approach to managing network applications The primary alternative, peer-to-peer networking, models all devices as having equivalent capability rather than specialized client or server roles. Compared to client-server, peer to peer networks offer some advantages such as more flexibility in growing the system to handle large number of clients. Client-server networks generally offer advantages in keeping data secure.

Introduction to Peer to Peer Networks

2008-11-23T18:48:00.000-08:00

By Bradley Mitchell, About.com

Peer to peer is an approach to computer networking where all computers share equivalent responsibility for processing data. Peer-to-peer networking (also known simply as peer networking) differs from client-server networking, where certain devices have responsibility for providing or "serving" data and other devices consume or otherwise act as "clients" of those servers.

Characteristics of a Peer Network

Peer to peer networking is common on small local area networks (LANs), particularly home networks. Both wired and wireless home networks can be configured as peer to peer environments.

Computers in a peer to peer network run the same networking protocols and software. Peer networks are also often situated physically near to each other, typically in homes, small businesses or schools. Some peer networks, however, utilize the Internet and are geographically dispersed worldwide.

Home networks that utilize broadband routers are hybrid peer to peer and client-server environments. The router provides centralized Internet connection sharing, but file, printer and other resource sharing is managed directly between the local computers involved.

Peer to Peer and P2P Networks

Internet-based peer to peer networks emerged in the 1990s due to the development of P2P file sharing networks like Napster. Technically, many P2P networks (including the original Napster) are not pure peer networks but rather hybrid designs as they utilize central servers for some functions such as search.

Peer to Peer and Ad Hoc Wi-Fi Networks

Wi-Fi wireless networks support so-called ad hoc connections between devices. Ad hoc Wi-Fi networks are pure peer to peer compared to those utilizing wireless routers as an intermediate device.

Benefits of a Peer to Peer Network

You can configure computers in peer to peer workgroups to allow sharing of files, printers and other resources across all of the devices. Peer networks allow data to be shared easily in both directions, whether for downloads to your computer or uploads from your computer.

On the Internet, peer to peer networks handle a very high volume of file sharing traffic by distributing the load across many computers. Because they do not rely exclusively on central servers, P2P networks both scale better and are more resilient than client-server networks in case of failures or traffic bottlenecks.

Computer Networking

2008-11-23T18:41:00.000-08:00

Computer Networking

From Wikipedia, the free encyclopedia

Network cards such as this one can transmit and receive data at high rates over various types of network cables. This card is a 'Combo' card which supports three cabling standards.

This article is about computer networking, the discipline of engineering computer networks. For the article on computer networks, see Computer network.

Computer networking is the engineering discipline concerned with communication between computer systems or devices. Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs.^[1] Computer networking is sometimes considered a sub-discipline of telecommunications, computer science, information technology computer engineering. Computer networks rely heavily upon the theoretical and practical application of these scientific and engineering disciplines. and/or

A computer network is any set of computers or devices connected to each other with the ability to exchange data.^[2] Examples of different networks are:

Local area network (LAN), which is usually a small network constrained to a small geographic area.
Wide area network (WAN) that is usually a larger network that covers a large geographic area.
Wireless LANs and WANs (WLAN & WWAN) are the wireless equivalent of the LAN and WAN.

All networks are interconnected to allow communication with a variety of different kinds of media, including twisted-pair copper wire cable, coaxial cable, optical fiber, and various wireless technologies.^[3] The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the interconnections of the Internet^[4]).

Views of networks

Users and network administrators often have different views of their networks. Often, users share printers and some servers form a workgroup, which usually means they are in the same geographic location and are on the same LAN. A community of interest has less of a connotation of being in a local area, and should be thought of as a set of arbitrarily located users who share a set of servers, and possibly also communicate via peer-to-peer technologies.

Network administrators see networks from both physical and logical perspectives. The physical perspective involves geographic locations, physical cabling, and the network elements (e.g., routers, bridges and application layer gateways that interconnect the physical media. Logical networks, called, in the TCP/IP architecture, subnets , map onto one or more physical media. For example, a common practice in a campus of buildings is to make a set of LAN cables in each building appear to be a common subnet, using virtual LAN (VLAN) technology.

Both users and administrators will be aware, to varying extents, of the trust and scope characteristics of a network. Again using TCP/IP architectural terminology, an intranet is a community of interest under private administration usually by an enterprise, and is only accessible by authorized users (e.g. employees).^[5] Intranets do not have to be connected to the Internet, but generally have a limited connection. An extranet is an extension of an intranet that allows secure communications to users outside of the intranet (e.g. business partners, customers).^[5]

Informally, the Internet is the set of users, enterprises,and content providers that are interconnected by Internet Service Providers (ISP). From an engineering standpoint, the Internet is the set of subnets, and aggregates of subnets, which share the registered IP address space and exchange information about the reachability of those IP addresses using the Border Gateway Protocol. Typically, the human-readable names of servers are translated to IP addresses, transparently to users, via the directory function of the Domain Name System (DNS).

Over the Internet, there can be business-to-business (B2B), business-to-consumer (B2C) and consumer-to-consumer (C2C) communications. Especially when money or sensitive information is exchanged, the communications are apt to be secured by some form of communications security mechanism. Intranets and extranets can be securely superimposed onto the Internet, without any access by general Internet users, using secure Virtual Private Network (VPN) technology.

When used for gaming one computer will have to be the server while the others play through it.

History

Before the advent of computer networks that were based upon some type of telecommunications system, communication between calculation machines and early computers was performed by human users by carrying instructions between them. Many of the social behavior seen in today's Internet was demonstrably present in nineteenth-century telegraph networks, and arguably in even earlier networks using visual signals. ^[6]

In September 1940 George Stibitz used a teletype machine to send instructions for a problem set from his Model K at Dartmouth College in New Hampshire to his Complex Number Calculator in New York and received results back by the same means. Linking output systems like teletypes to computers was an interest at the Advanced Research Projects Agency (ARPA) when, in 1962, J.C.R. Licklider was hired and developed a working group he called the "Intergalactic Network", a precursor to the ARPANet.

In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing System MIT, a research group supported by General Electric and Bell Labs used a computer (DEC's PDP-8) to route and manage telephone connections. for distributed users of large computer systems. The same year, at

Throughout the 1960s Leonard Kleinrock, Paul Baran and Donald Davies packets that could be used in a packet switched network between computer systems. independently conceptualized and developed network systems which used datagrams or

1965 Thomas Merrill and Lawrence G. Roberts created the first wide area network(WAN).

The first widely used PSTN switch that used true computer control was the Western Electric 1ESS switch, introduced in 1965.

In 1969 the University of California at Los Angeles, SRI (in Stanford), University of California at Santa Barbara, and the University of Utah were connected as the beginning of the ARPANet network using 50 kbit/s circuits. Commercial services using X.25, an alternative architecture to the TCP/IP suite, were deployed in 1972.

Computer networks, and the technologies needed to connect and communicate through and between them, continue to drive computer hardware, software, and peripherals industries. This expansion is mirrored by growth in the numbers and types of users of networks from the researcher to the home user.

Today, computer networks are the core of modern communication. For example, all modern aspects of the Public Switched Telephone Network (PSTN) are computer-controlled, and telephony increasingly runs over the Internet Protocol, although not necessarily the public Internet. The scope of communication has increased significantly in the past decade and this boom in communications would not have been possible without the progressively advancing computer network.

Networking methods

Networking is a complex part of computing that makes up most of the IT Industry. Without networks, almost all communication in the world would cease to happen. It is because of networking that telephones, televisions, the internet, etc. work.

One way to categorize computer networks is by their geographic scope, although many real-world networks interconnect Local Area Networks (LAN) via Wide Area Networks (WAN)and wireless networks[WWAN]. These three (broad) types are:

Local area network (LAN)

A local area network is a network that spans a relatively small space and provides services to a small number of people.

A peer-to-peer or client-server method of networking may be used. A peer-to-peer network is where each client shares their resources with other workstations in the network. Examples of peer-to-peer networks are: Small office networks where resource use is minimal and a home network. A client-server network is where every client is connected to the server and each other. Client-server networks use servers in different capacities. These can be classified into two types:

1. Single-service servers

2. print server,

where the server performs one task such as file server, ; while other servers can not only perform in the capacity of file servers and print servers, but they also conduct calculations and use these to provide information to clients (Web/Intranet Server). Computers are linked via Ethernet Cable, can be joined either directly (one computer to another), or via a network hub that allows multiple connections.

Wide area network (WAN)

A wide area network is a network where a wide variety of resources are deployed across a large domestic area or internationally. An example of this is a multinational business that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is a network comprised of many smaller networks. The Internet is considered the largest network in the world.^[7]. The PSTN (Public Switched Telephone Network) also is an extremely large network that is converging to use Internet technologies, although not necessarily through the public Internet.

A Wide Area Network involves communication through the use of a wide range of different technologies. These technologies include Point-to-Point WANs such as Point-to-Point Protocol (PPP) and High-Level Data Link Control (HDLC), Frame Relay, ATM (Asynchronous Transfer Mode) and Sonet (Synchronous Optical Network). The difference between the WAN technologies is based on the switching capabilities they perform and the speed at which sending and receiving bits of information (data) occur.

Metropolitan Area Network (MAN)

A metropolitan network is a network that is too large for even the largest of LAN's but is not on the scale of a WAN. It also integrates two or more LAN networks over a specific geographical area ( usually a city ) so as to increase the network and the flow of communications. The LAN's in question would usually be connected via "backbone" lines.

For more information on WANs, see Frame Relay, ATM and Sonet.

Wireless networks (WLAN, WWAN)

A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transferred over sets of radio transceivers. These types of networks are beneficial when it is too costly or inconvenient to run the necessary cables. For more information, see Wireless LAN and Wireless wide area network. The media access protocols for LANs come from the IEEE.

The most common IEEE 802.11 WLANs cover, depending on antennas, ranges from hundreds of meters to a few kilometers. For larger areas, either communications satellites of various types, cellular radio, or wireless local loop (IEEE 802.16) all have advantages and disadvantages. Depending on the type of mobility needed, the relevant standards may come from the IETF or the ITU.

Network topology

The network topology defines the way in which computers, printers, and other devices are connected, physically and logically. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions. Commonly used topologies include:

Bus
Star
Tree (hierarchical)
Linear
Ring
Mesh
- partially connected
- fully connected (sometimes known as fully redundant)

The network topologies mentioned above are only a general representation of the kinds of topologies used in computer network and are considered basic topologies.

Computer Network

2008-11-23T18:29:00.000-08:00

Computer Network

From Wikipedia, the free encyclopedia

A computer network is a group of interconnected computers. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of some types and categories and also presents the basic components of a network.

Introduction to Computer Networks

A network is a collection of computers connected to each other. The network allows computers to communicate with each other and share resources and information. The Advance Research Projects Agency (ARPA) designed "Advanced Research Projects Agency Network" (ARPANET) for the United States Department of Defense. It was the first computer network in the world in late 1960's and early 1970's.^{[citation needed]}

Network Classification

The following list presents categories used for classifying networks.

Scale

Based on their scale, networks can be classified as Local Area Network (LAN), Wide Area Network (WAN), Metropolitan Area Network (MAN), Personal Area Network (PAN),Virtual Private Network (VPN) etc.

Connection method

Computer networks can also be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as Optical fiber, Ethernet, Wireless LAN, HomePNA, or Power line communication.

Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges and/or routers.

Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium.

Functional relationship (Network Architectures)

Computer networks may be classified according to the functional relationships which exist among the elements of the network, e.g., Active Networking, Client-server and Peer-to-peer (workgroup) architecture.

Network topology

Main article: Network Topology

Computer networks may be classified according to the network topology upon which the network is based, such as Bus network, Star network, Ring network, Mesh network, Star-bus network, Tree or Hierarchical topology network,

Network Topology signifies the way in which devices in the network see their logical relations to one another. The use of the term "logical" here is significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a Bus Topology. In this regard the visual and operational characteristics of a network are distinct; the logical network topology is not necessarily the same as the physical layout.

Types of networks

Below is a list of the most common types of computer networks in order of scale.

Personal Area Network (PAN)

Main article: Personal area network

A personal area network (PAN) is a computer network used for communication among computer devices close to one person. Some examples of devices that are used in a PAN are printers, fax machines, telephones, PDAs and scanners. The reach of a PAN is typically about 20-30 feet (approximately 6-9 meters), but this is expected to increase with technology improvements.

Local Area Network (LAN)

Main article: Local Area Network

This is a network covering a small geographic area, like a home, office, or building. Current LANs are most likely to be based on Ethernet technology. For example, a library may have a wired or wireless LAN for users to interconnect local devices (e.g., printers and servers) and to connect to the internet. On a wired LAN, PCs in the library are typically connected by category 5 (Cat5) cable, running the IEEE 802.3 protocol through a system of interconnected devices and eventually connect to the Internet. The cables to the servers are typically on Cat 5e enhanced cable, which will support IEEE 802.3 at 1 Gbit/s. A wireless LAN may exist using a different IEEE protocol, 802.11b, 802.11g or possibly 802.11n. The staff computers (bright green in the figure) can get to the color printer, checkout records, and the academic network and the Internet. All user computers can get to the Internet and the card catalog. Each workgroup can get to its local printer. Note that the printers are not accessible from outside their workgroup.

Typical library network, in a branching tree topology and controlled access to resources

All interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers.

The defining characteristics of LANs, in contrast to WANs (wide area networks), include their higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 100 Gbit/s, and possibly 40 Gbit/s.

Campus Area Network (CAN)

Main article: Campus Area Network

This is a network that connects two or more LANs but that is limited to a specific and contiguous geographical area such as a college campus, industrial complex, office building, or a military base. A CAN may be considered a type of MAN (metropolitan area network), but is generally limited to a smaller area than a typical MAN. This term is most often used to discuss the implementation of networks for a contiguous area. This should not be confused with a Controller Area Network. A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.

Metropolitan Area Network (MAN)

Main article: Metropolitan Area Network

A Metropolitan Area Network is a network that connects two or more Local Area Networks or Campus Area Networks together but does not extend beyond the boundaries of the immediate town/city. Routers, switches and hubs are connected to create a Metropolitan Area Network.

Wide Area Network (WAN)

Main article: Wide Area Network

A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

Global Area Network (GAN)

Main article: Global Area Network

Global Area networks (GAN) specifications are in development by several groups, and there is no common definition. In general, however, a GAN is a model for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is "handing off" the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial Wireless local area networks (WLAN).^[1]

Internetwork

Main article: Internetwork

Two or more networks or network segments connected using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as a router. Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.

In modern practice, the interconnected networks use the Internet Protocol. There are at least three variants of internetwork, depending on who administers and who participates in them:

Intranet
Extranet
Internet

Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet is not considered to be a part of the intranet or extranet, although it may serve as a portal for access to portions of an extranet.

Intranet

Main article: Intranet

An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information.

Extranet

Main article: Extranet

An extranet is a network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g. a company's customers may be given access to some part of its intranet creating in this way an extranet, while at the same time the customers may not be considered 'trusted' from a security standpoint). Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN; it must have at least one connection with an external network.

Internet

Main article: Internet

The Internet is a specific internetwork. It consists of a worldwide interconnection of governmental, academic, public, and private networks based upon the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the U.S. Department of Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW). The 'Internet' is most commonly spelled with a capital 'I' as a proper noun, for historical reasons and to distinguish it from other generic internetworks.

Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP Addresses) administered by the Internet Assigned Numbers Authority and address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.

Basic Hardware Components

All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.11) or optical cable ("optical fiber").

Network Interface Cards

Main article: Network card

A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.The NIC provides the transfer of data in megabytes.

Repeaters

Main article: Repeater

A repeater is an electronic device that receives a signal and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair ethernet configurations, repeaters are required for cable runs longer than 100 meters away from the computer.

Hubs

Main article: Network hub

A hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub for transmission. When the packets are copied, the destination address in the frame does not change to a broadcast address. It does this in a rudimentary way: It simply copies the data to all of the Nodes connected to the hub.^[2]

Bridges

Main article: Network bridge

A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.

Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.

Bridges come in three basic types:

Local bridges: Directly connect local area networks (LANs)
Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers.
Wireless bridges: Can be used to join LANs or connect remote stations to LANs.

Switches

Main article: Network switch

A switch is a device that performs switching. Specifically, it forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the MAC addresses in the packets.^[3] This is distinct from a hub in that it only forwards the datagrams to the ports involved in the communications rather than all ports connected. Strictly speaking, a switch is not capable of routing traffic based on IP address (layer 3) which is necessary for communicating between network segments or within a large or complex LAN. Some switches are capable of routing based on IP addresses but are still called switches as a marketing term. A switch normally has numerous ports, with the intention being that most or all of the network is connected directly to the switch, or another switch that is in turn connected to a switch.^[4]

Switch is a marketing term that encompasses routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier). Switches may operate at one or more OSI model layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.

Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.

Routers

Main article: Router

Routers are networking devices that forward data packets between networks using headers and forwarding tables to determine the best path to forward the packets. Routers work at the network layer of the TCP/IP model or layer 3 of the OSI model. Routers also provide interconnectivity between like and unlike media (RFC 1812). This is accomplished by examining the Header of a data packet, and making a decision on the next hop to which it should be sent (RFC 1812) They use preconfigured static routes, status of their hardware interfaces, and routing protocols to select the best route between any two subnets. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Some DSL and cable modems, for home (and even office) use, have been integrated with routers to allow multiple home/office computers to access the Internet through the same connection. Many of these new devices also consist of wireless access points (waps) or wireless routers to allow for IEEE 802.11g/b wireless enabled devices to connect to the network without the need for cabled connections.

Tutorials

2008-11-16T23:45:00.000-08:00

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Where can I get an online virus scan?

2008-11-16T23:15:00.000-08:00

There are times when you do not want to download anti-virus software. These may include:

Your computer is too infected or broken to install new software
You are on someone elses computer and you don't want to install software
You just need to do a quick check, without the hassle of software installation

The solution for virus scanning at those times is to utilize an online virus scanner.

Note: Most online virus scanners require Internet Explorer with ActiveX enabled.

Online Virus Scanners

Trend Micro Housecall

Trend Micro HouseCall thoroughly scans your computer for viruses, spyware, and known security vulnerabilities. This free service is designed to demonstrate the power of Trend Micro technologies in a fast and easy solution.

BitDefender Online Scanner

BitDefender Online Scanner is a fully functional antivirus product. It features all required elements for thorough antivirus scanning and effective cleaning: it scans your system's memory, all files, folders and drives' boot sectors, providing you with the option to automatically clean the infected files.

Freedom Online Virus Check

Freedom Online Virus Check is a free online anti-virus scanner for web users. Freedom Online Virus Check allows you to scan your hard drives, diskettes, CD-ROMs, network drives, directories, and specific files for any hidden viruses, Trojans or worms. Freedom Online Virus Check uses state-of-the-art technology to scan your PC for all types of viruses.

McAfee FreeScan

McAfee FreeScan helps you detect thousands of viruses on your computer. Based on the award-winning McAfee VirusScan engine, FreeScan searches for viruses, including the latest known "in the wild" viruses, and displays a detailed list of any infected files. Should viruses be found, FreeScan even provides links to more information about the viruses and what you can do to clean your system.

Panda Active Scan

Antivirus - Antivirus detects and eliminates all types of viruses, worms and Trojans.
Antispyware Deep anti-spyware scan detects spyware that other security suites can�'t.
TruPrevent - Catches viruses that are so new than your signature-based antivirus software cannot yet recognize them.
Daily Updates - Active Scan is updated at least once a day, so each scan will be able to detect even the latest viruses and spyware to emerge.
One-click Scan - No need to install any programs, just connect to the Internet and simply click whenever you want to check if your computer is infected by viruses or spyware.

RAV AntiVirus Online Viru Scan

RAV AntiVirus Online Virus Scan will scan and clean your PC of viruses and other malwares here; free of charge.

Virus infection is a reality of modern-day computing and with the advent of the Internet; this reality has become even more real. It is an inconvenience that happens not only on your home computer, but in the office as well.

TrojanScan

Trojan horses are a huge security threat. A Trojan is a program that enters your computer undetected, giving the attacker who planted the Trojan unrestricted access to the data stored on your computer. Trojans can transmit credit card information and other confidential data in the background. Trojans are often not caught by virus scanning engines, because these are focused on viruses, not Trojans. Catching such threats would require the use of a Trojan scanner (a.k.a Trojan cleaner, Trojan remover, anti-Trojan).

How do I Protect My Computer on the Internet?

2008-11-16T23:08:00.000-08:00

The Internet is an ever present threat to your computer. Even harmlessly browsing through sites may get your computer affected with a virus or spyware without you even knowing it. As many dangers as there may be out there, you can easily protect yourself by taking a few simple steps.

Routers and Firewalls

First of all, if you don't already have a router, it is recommended that you go and get one, even if you only have one computer in your home. A Router acts as the best kind of firewall, a hardware firewall. It protects you from all kinds of viruses and keeps your information safe. Hackers who want to gain access to your computer who may try to port scan your computer. High end routers may be able to completely block these scans or at least slow the hacker down. The majority of hackers on the Internet do not want to waste time trying to get through a router, and would rather move onto another victim.

Apart from hardware firewalls, there are also lots of software that is available for you to install free of charge. Many of the smaller companies provide just as good protection from threats as large brand names such as Norton or Sophos.

The four main types of programs that you will need to protect your computer are an active virus scanner, a firewall, a spyware scanner, and a general anti-virus program.

Virus Scanners

An active virus scanner is a virus scanner than runs in the background whenever your computer is running. These programs tend to take up very little memory because they only run quick scans of any and every file. A2 Guard or ASquared is a highly recommended program. It scans files in the background and does not compromise your CPU's resources in doing so.

Software Firewalls

A firewall is something that prevents intrusions into your computer. There are many versions available on the Internet, so you will be able to find lots of a free firewalls to download. One highly recommended firewall is ZoneAlarm. The free firewall provides basic protection from intrusions. ZoneAlarm free does not come with an anti virus that would normally come with the retail version. Therefore you will have to install other programs with it.

Spyware Scanners

A spyware scanner is something that scans for spyware. You only need to run this program every month or so. The easiest program to use, as well as being free, is Ad-Aware.

Spyware is usually installed when you visit a website that has infected cookies. Using the program A2 as described above, you can choose whether to reject these cookies anytime the program suspects something. This is highly recommended.

Anti-Virus

A general anti virus is a program that scans for viruses and either deletes or quarantines them. A favorite among computer users is the freeware AVG. It thoroughly scans files when performing a scan and is very reliable.

Armed with these programs, you should have no trouble browsing through sites on the Internet.

Where can I Download Free Anti-Virus Software?

2008-11-16T23:00:00.000-08:00

There are quite a few free anti-virus software programs that you can download for free.

Here are the ones we use and recommend:

ClamAV

Clam AntiVirus is a GPL anti-virus toolkit for Unix. The main purpose of ClamAV is the integration with mail servers (attachment scanning). ClamAV provides a flexible and scalable multi-threaded daemon, a command line scanner, and a tool for automatic updating via Internet. The programs are based on a shared library distributed with the Clam AntiVirus package, which you can use with your own software.

Clam AntiVirus works with Linux, Solaris, FreeBSD, OpenBSD, NetBSD, AIX, Mac OS X, and Cygwin B20 on multiple architectures such as Intel, Alpha, Sparc, Cobalt MIPS boxes, PowerPC, and RISC 6000.

Most importantly, the ClamAV virus database is kept up to date.

Command-line scanner
Fast, multi-threaded daemon
Mail filter interface for sendmail
Database updater with support for digital signatures
Virus scanner C library
On-access scanning (Linux and FreeBSD)
Detection of over 38000 viruses, worms and trojans
Built-in support for Zip, Gzip, Bzip2, tar, RAR, MS OLE2, MS Cabinet files, MS CHM (Compressed HTML), MS SZDD
Support for mbox, Maildir and raw mail files
Support for Portable Executable files compressed with UPX, FSG, and Petite

ClamWin

ClamWin is a Free Antivirus for Microsoft Windows 98/Me/2000/XP/2003. ClamWin provides a graphical user interface to the Clam AntiVirus engine.

ClamWin Free Antivirus uses the GNU General Public License by the Free Software Foundation and is free (as in freedom) software. To find out more about GNU General Public License and what it entitles you to, please visit the following link: Philosophy of the GNU Project - Free Software Foundation.

ClamWin Free Antivirus comes with an easy installer and open source code at no cost. It features:

Scanning Scheduler
Automatic Virus Database Updates. ClamAV team updates Virus Databases on a regular basis and almost immediately after a new virus/variant is out
Standalone Virus Scanner
Context Menu Integration to Microsoft Windows Explorer
Add-in to Microsoft Outlook

F-Prot Antivirus

F-Prot Antivirus products are easy to use, reliable and demand little of the user's system resources. With their combined speed and reliable detection methods, F-Prot Antivirus products are the ideal computer security solution for home users.

F-PROT Antivirus for Linux, BSD, Solaris, and DOS are all free for home users.

AVF Anti-Virus Free Edition

The AVG Free Edition anti-virus protection tool is available free-of-charge to home users for the life of the product. Rapid virus database updates are available for the lifetime of the product, thereby providing the high-level of detection capability that millions of users around the world trust to protect their computers. AVG Free is easy-to-use and will not slow your system down (low system resource requirements).

Automatic update functionality
The AVG Resident Shield, which provides real-time protection as files are opened and programs are run
The AVG E-mail Scanner, which protects your e-mail
The AVG On-Demand Scanner, which allows the user to perform scheduled and manual tests
Free Virus Database Updates for the lifetime of the product
AVG Virus Vault for safe handling of infected files

AVG Free Edition is for private, non-commercial, single home computer use only. Use of AVG Free Edition within any organization or for commercial purposes is strictly prohibited.

AntiVir Personal Edition Classic

The private and individual use of the AntiVir Personal Edition is free of charge.

The AntiVir Personal Edition offers the effective protection against computer viruses for the individual and private use on a single PC-workstation. In order to make possible an easy operation, the AntiVir Personal Edition is developed to the essential points.

Detects and removes more than 150,000 viruses
Always among the winners of comparison test featured in computer journals
The resident Virus Guard serves to monitor file movements automatically, e.g. downloading of data from the internet
Scanning and repair of macro viruses
Protection against previously unknown macro viruses
Safeguard against cost generating dial-up program
Protection against trojans, worms, backdoors, jokes and other harmful programs
Easy operation
Internet-Update Wizard for easy updating
Protection against previously unknown boot record viruses and master boot record viruses
Quality "Made in Germany"
Support is free of charge via AntiVir Bulletin Board

avast! Home Edition

avast! Home Edition is now free of charge for home users for non-commercial use.

avast! Home Edition supports Windows 95 and higher.

avast! Home Edition Features:

Antivirus kernel
Automatic updates
Simple User Interface
Virus Chest
Resident protection
System integration
P2P and IM Shields
Integrated Virus Cleaner
Network Shield
Support for 64-bit Windows
Web Shield
Internationalization

BitDefender Free Edition

BitDefender Free Edition offers a scan engine with high detection rate, a friendly user interface and support for all e-mail clients.

BitDefender Free Edition automatically updates itself under Windows 2000 and XP; if a new user has logged in, even with restricted user rights, the software displays warning messages when new viruses occur.

BitDefender's behavior based search enables it to recognize unknown viruses and mutants. BitDefender also recognizes many file formats, archives and compressed files, embedded OLE objects in Office documents and runtime packers.

BitDefender features include:

Virus scanning and removal
- On demand scanning - Powerful scan engines ensure detection and removal of all viruses in the wild every time you need it.
Scheduled scanning
- The Scheduler lets you plan ahead, and schedule full system/drive scans in the off hours, when you won't be using your computer.
Immediate scanning
- With just a right click you can check your files and folders.
Skinable interface
- You can express yourself, designing new interfaces, or you can use those drawn by others.
Quarantine
- By isolating the infected files in quarantine, the risk of getting infected diminishes. You also have the possibility to send these files for further analysis to BitDefender Labs.
Reports
- When launching a scan you may choose to create a report file where you can see statistics about the scan process.

BitDefender Linux Edition

BitDefender Linux Edition uses the most advanced multi-platform virus inspection technology which scans for viruses and other malware on your personal system.

The On-Demand Scanner, for command line or shell scripts, features manual scan of individual files or entire file systems, malicious code detection and disinfection. After each scan, the solution displays a detailed report on positive virus detections. Thanks to BitDefender scan engine advanced features, new, undiscovered threats can be detected and immediately eliminated from the system.

BitDefender Linux Edition has the task of keeping you away from worms like Morris or Scalper - Unix malware, as well as from all the Windows viruses.

BitDefender Linux Edition is a free product, which does not require a license to be used.

Antivirus scanning - on-demand scanning of the hard disk content
Signature update - enables the update of the signatures files
Quarantine zone - the infected files can be isolated on a secure area
Increased scanning speed - owing to the new improved scanning engines
Detailed reports and statistics - if configured, it will create a log file that will contain all the scanning results help - the user can view the help containing the protection options directly from the command line

VCatch Basic

VCatch is a new, free tool, developed to protect your computer from web viruses. Whether you use an Email application, Web based Email, ICQ, or one of the new file-sharing programs (iMesh, KaZaA etc.); VCatch is the tool for you.

VCatch is a virus protection software. When VCatch is active it will check all the files sent or downloaded to your computer via E-mail and Web applications. When VCatch detects that a file is suspected to be a virus, the software automatically deletes the file and notifies you.

VCatch supports Microsoft Outlook, Outlook Express, Eudora and Netscape Messenger. In Addition, VCatch protects your computer from viruses downloaded using IE or Netscape Navigator web browsers, files sent to your computer by ICQ, and files downloaded using file-sharing software such as iMesh and KaZaA.

VCatch has a unique automatic update mechanism. When a new virus is detected on the Internet, VCatch automatically updates its virus definitions list in your computer. Once you install VCatch, you don't have to do anything else to be constantly protected.

VCatch uses a combination of techniques to protect your computer. VCatch Internet professional searchers are responsible for constantly updating the viruses list so VCatch can keep the mail messages and the files containing them out of your computer. In addition, VCatch uses the Advanced Malicious Application Detection system (called "APayya"), which scans every incoming file looking for suspicious characteristics using a sophisticated and flexible rules system. VCatch enables you to set the preferred security level and uses these settings when a suspicious file is detected in order to decide whether to notify you. This way you can be sure you are protected both from known viruses and from unknown malicious applications.

Comodo

Comodo AntiVirus leverages multiple technologies (including on demand and on access scanning, email scanning, process monitoring, worm blocking and host intrusion prevention) to immediately start cleaning or quarantining suspicious files from your hard drives, shared disks, emails, downloads and system memory.

Updated virus definitions are automatically downloaded according to a schedule of your choice or by a single click on the 'updater' button. Once installed, Comodo AntiVirus will unobtrusively sit in your system tray, silently and efficiently defending your system from the latest virus outbreaks.

It's easy to install and configure, will not slow down your PC by hogging system resources and is free for life to the end user.

Comodo AntiVirus includes an application called LaunchPad. LaunchPad notifies users of free software offerings from Comodo. Some users have complained that LaunchPad is adware and is impossible to uninstall without removing Comod AntiVirus.

Why Do People Write Computer Viruses?

2008-11-16T22:57:00.000-08:00

We hear about new computer viruses all the time. What is the motivation behind developing computer viruses and watching them wreak havoc on the Internet?

Fact Gathering

Many viruses raid your documents including your email address book for information that can be used to make business contacts. This data is assembled into a database that can then be sold to others as a qualified list of "opportunity seekers." The result is a mountain of spam emails, and even unsolicited direct mail pieces, if the address books also contain home addresses as well. Unfortunately, some unscrupulous companies look upon this invasion of privacy as a victimless crime, since you are not doing any permanent damage to anyone's hard drive. However, theft of data is still theft, no matter what the intended purpose.

Viruses Create Trouble

The fact is that some people love to create problems for other people. Perhaps it is someone who has an axe to grind with big business. Maybe it is someone who thinks the world is getting too dependent on the Internet for worldwide communications. Of course, creating computer viruses may also just be a way to get attention, even if one has to remain anonymous in order to avoid going to jail. The sheer thrill of knowing that your creation disrupted systems all over the world may feed an ego that doesn't have much else going for it.

The Thrill of the Chase

For some, it is not really wanting to cause trouble for other people so much as it is seeing if one can create a virus, launch it successfully, and have it make some sort of an impact before it is contained. For this type of person, it is the process that brings the satisfaction, not the end result. Developing the virus and setting it free is the thing that makes it all worthwhile.

Computer viruses cost individuals and companies untold millions of dollars each year. While some computer viruses are more along the line of merely irritating, there are viruses that have crippled whole infrastructures and created major problems. Whatever the reason behind creating a computer virus, there has yet to be a legitimate excuse for developing one.

How to Remove a Virus

2008-11-16T19:46:00.000-08:00

What is a Virus?

A virus is a destructive executable program that infects the other programs in the system and spreads by replicating itself.

Why is it Harmful?

Such a program is designed to damage the victim computer's files.

How does it Spread?

Viruses are coded by malicious programmers in a way that they can spread in the system without one's permission and knowledge.

Different Aspects of Virus

Usually every virus has two aspects – a finder and a replicator.

The finder searches for the new uninfected files and the replicator actually targets these files and infects it by multiplying itself.

How a Virus Affects a System

It corrupts files
It slows down the speed of the computer system
It causes the system to hang frequently
It deletes various files

Sources of Virus Infection

A virus can enter the system and infect it through various sources. Some of the sources are

Infected CDs, DVDs, pen drives, etc
E-mail
Browsing infected sites
Downloading files from the internet

How to Remove Viruses

Removing viruses, though technical, is yet a very simple process if all the required steps are properly followed.

The basic steps are:

Buy or download an antivirus software
Install the antivirus software
Update antivirus software with the latest virus definitions
Do a complete system scan

A safe way to remove viruses is to use a bootable antivirus CD (containing the latest definitions) to scan the drive. Alternatively, you can attach the drive to a friend's computer that has an antivirus installed (with the latest updates) and perform a full disk scan.

However, if you cannot do any of the above options, you may want to try the following steps:

Steps to Remove a Virus from the System

Step 1
Install an Antivirus Program in the System

What is Antivirus program? An antivirus is a program that searches for, identifies and removes potential viruses existing in the computer system.

Antivirus software: Some of the commonly available antivirus programs in the market are -

Symantec Norton antivirus
AVG antivirus
McAfee Scan
Microsoft Antivirus

The antivirus software should be updated regularly to retain its effectiveness.

Before installing the antivirus, close all open applications and terminate any suspicious processes using Task Manager. Sometimes, you may need to boot into safe mode or safe mode with command prompt to delete suspicious programs and references to them in the Windows Registry (run regedit from the command prompt to open the registry editor).

Search engines are excellent tools to find out whether a certain process is harmful or not. You can also get steps on how to remove a specific virus manually.

Removing the virus beforehand might be necessary, as some viruses will not allow an antivirus to operate. However, if you are not successful, you may still continue with the installation.

Step 2
Scan the System to Identify and Locate the Virus

Usually, the antivirus will run automatically when the system reboots after the installation.

Therefore, it might identify the virus automatically.

Moreover, you may want to run a quick system scan to locate the virus.

Step 3
Troubleshooting the Virus Infected Areas

After the antivirus identifies the infected areas, the next step is to rectify those areas.

Methods of Eliminating Viruses

Generally, the antivirus adopts one of two methods to eliminate the virus:

Removing the virus – When the virus can be easily identified and can be removed without affecting other files, then the antivirus removes it from the host place.
Quarantine – This is done when the virus cannot be easily identified removed from the file and the removal of virus means the removal of the complete file. In this method, although the virus is not eliminated, it is rendered inactive by moving the file into "quarantine" and renaming it.

Step 4
Perform a Full System Scan

Even after the virus is removed from the system, the next step is to scan the whole system to ensure that no infected files remain.

What if the Antivirus Fails?

It may happen that your antivirus fails to detect and get rid of the virus. In such a case, you can follow the steps given below:

Take a backup of the entire data.
Format the infected disk partition.
In case the entire system is infected, the system will have to be reinstalled.
Install the antivirus and the latest updates.
Restore the backup.

What are the Types of Computer Viruses?

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Computer viruses are generally defined as a program inputted into a computer that allows replication of the program installed. As it replicates, the program intentionally infects the computer, typically without even the user knowing about the damage being done. A virus, unlike worms or Trojan horses, needs an aid to transfer them to computers. Viruses usually take a large amount of computer memory, resulting into system crashes. Viruses are categorized to several parts based on its features.

Macro Viruses

A macro virus, often scripted into common application programs such as Word or Excel, is spread by infecting documents. Macro viruses are known to be platform-independent since the virus itself are written in language of the application and not the operating system. When the application is running, this allows the macro virus to spread amongst the operating systems. There are thousands of macro viruses that exists, and each are considered major threats. Examples of these viruses are: Melissa.A and Bablas. pc.

Network Viruses

Network viruses rapidly spreads through a Local Network Area (LAN), and sometimes throughout the internet. Generally, network viruses multiply through shared resources, i.e., shared drives and folders. When the virus infects a computer, it searches through the network to attack its new potential prey. When the virus finishes infecting that computer, it moves on to the next and the cycle repeats itself. The most dangerous network viruses are Nimda and SQLSlammer.

Logic Bombs

The logic bomb virus is a piece of code that are inputted into a software system. When a certain and specific condition is met, such as clicking on an internet browser or opening a particular file, the logic bomb virus is set off. Many programmers set the malicious virus off during days such as April Fools Day or Friday the 13th. When the virus is activated, then various activities will take place. For example, files are permanently deleted.

Companion Viruses

Companion viruses takes advantage of MS-DOS. This virus creates a new file with typically the .COM extensions, but sometimes the .EXD extension as well. When a user manually types in a program they desire without adding .EXE or any other specific extention, DOS will make the assumption that the user want the file with the extension that comes first in alphabetical order, and thus running the virus. The companion virus is rare among Windows XP computers as this particular operating system does not use the MS-DOS.

Boot Sector Viruses

Boot sector viruses generally hide in the boot sector, either in the bootable disk or the hard drive. Unlike most viruses, this virus does not harm the files in the hard disk, but harm the hard disk itself. Boot sector viruses are uncommon at this day and age because these viruses are spread rapidly by floppy disks and not on CD-ROMs.

Multipartite Viruses

Multipartite viruses are spreaded through infected media and usually hides in the memory. Gradually, the virus moves to the boot sector of the hard drive and infects executable files on the hard drive and later across the computer system.

What is the History of Computer Viruses?

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The first computer virus to openly make it to the public was a program called "Elk Cloner". It was created by Rich Skrenta, a computer programmer who was in high school when this virs was created in 1982. Elk Cloner attached itself to the Apple DOS 3.3 operating system and was later spreaded by a floppy disk. When the virus was created, it was intentionally made as a joke by the high school student, who inputted the virus into a game in which the virus was set off after the 50th time of using the game. When the virus was set off, a blank screen appeared and displayed a poem about the virus. The computer then became infected.

The first PC virus was a boot sector virus named (c)Brain. Two brothers, Basit and Amjad Farooq Alvi, whose only intentions were to protect their work from piracy and to target copyright infringers, programmed it. However, according to analysts, the Ashar virus, which was a variant of Brain, possibly was created before the (c)Brain.

Before network computer expansion, most viruses were spreaded through removable media, such as floppy disks. These viruses infected programs stored in the disks, while others were inputted into the disk boot sectors, and activated when the user booted the computer from the disk. The traditional and typical virus characteristics common to us now emerged in the 1980s, where there was an increase of BBS (Bulletin Board System, where a computer system runs software that allows users to dial into the system over a phone line), modem use, and software sharing. BBS contributed greatly to the rapid spread of Trojan horses, and viruses were orginally written to target popular software traders. Traders who were in a hurry to retrieve the lastest software were usually the easiest prey to infect viruses with.

In the mid 1990s, macro viruses came into the scene and became common quickly. Ironically, some versions of Microsoft Word allowed the macro virus to multiply and gain additional blank lines. This can cause a misleading detection, as others would see the new strands of the macro virus as a new virus.

Viruses then began spreading via instant messaging. Typically, it sends a web address to everybody in the contact list, and anyone who so much as click on the link would be prone of an immediate infection. However, there are thousands and thousands of viruses operating online and new viruses are discovered every single day.

What is a boot sector virus?

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A boot sector virus is a computer virus which infects the boot sector on hard disks, floppy disks, and theoretically also other bootable media such as CD's and DVD's.

A boot sector virus does not need to be able to successfully boot the victims computer to infect it. Because of this, even non-bootable media can spread a boot sector virus.

Once the infected computer successfully boots, the boot sector virus stays in memory and infects floppies and other media when they are written to by the infected computer.

Boot sector viruses have become increasingly less common as floppy disks have