Lab

Processors

Whether you're buying a new computer or upgrading an old one, if you want speed, the key item to look at is the processor. This chip, also known as the 'central processing unit' or CPU, is the number-crunching engine of your PC, and more than any other component it determines what kind of power your computer can muster. Deciding which lump of silicon is right for you might sound like a brain ache - after all, there's not just raw power to consider. Compatibility with your existing components and possible future upgrades is equally critical, as is value for money. Never fear, though - Computer Buyer is here to help you.

What kind of processor do I need?

A processor must have sufficient power to handle everything you want to do with your PC, plus a little extra to help your system cope with the fancier things you'll want to try within a year or two.

That doesn't mean, however, that you should run out and buy the very latest (and most expensive) Pentium 4 or Athlon. If all you do now is use your word processor, listen to a few MP3s and do the odd bit of photo editing, a budget processor like the Duron or Celeron will do just fine, and will probably still be hunky dory in a couple of years' time.

If, on the other hand, you're a hardcore gamer or video-editing fanatic, you'll need to go for the big guns - AMD's Athlon XP or Intel's Pentium 4. The trick is to decide which price bracket suits your needs, then get the very best deal you can for your budget.

Although there are lots of specifications that look like they should tell you whether a processor is fast or not, they're not really much use when comparing different brands of processor. The proof of the pudding is in the eating, and that's where we come in. We tested six different processors with the bits of our Computer Buyer benchmarks that make them work the hardest - office work (including some arduous number-crunching in the spreadsheet program Excel), and multimedia tasks such as video and music encoding. Not only do these tasks put the processors under strain, but they also enable you to compare the results with those segments of our main Labs benchmarks, putting the processor's performance in perspective. We also ran the 3D benchmark 3DMark 2001, which gives an idea of how each processor would perform with the latest games.

What else do I need to think about?

If you're upgrading the processor in your existing machine, you need to make sure it will fit in your existing motherboard - and also that the motherboard is capable of supporting the newer, faster processor, too. Currently, most processors slot into one of two motherboard fittings: AMD chips (Athlon and Duron) require a Socket A fitting; Intel's Celeron and Pentium 4 use Socket 478. First, you'll need to check that the socket on your motherboard matches the format of your chosen chip.

To make sure your motherboard also supports the processor electrically, you'll need to go to the board manufacturer's Web site and look up your model. There should be a list on the site showing all the processors the board supports. Some of the newer chips might require you to upgrade the motherboard's BIOS - the basic set of instructions that control the way your your PC's components 'talk' to each other. Details of how you do this should be provided on the Web site.

You should also also think about whether or not to upgrade other parts of your PC to keep up with your processor. If you put a brand new processor in a PC with old SDRAM, it won't run as fast as it could do. Once again, check your motherboard supports these other components.

Which chip's a winner?

We tested these processors for speed, but speed isn't the whole story - naturally, we're also interested in value for money. That's why the Athlon comes out ahead of the Pentium 4, even though the Pentium 4 was faster in our tests. The speed difference is so tiny you won't notice it, but your wallet will certainly notice the massive £400 saving!