Now that you know all about the different motherboard sockets available thanks to last week's article, it's now time to learn up on CPUs.

Short for Central Processing Unit, the CPU is commonly known as "the thing which does most of the stuff" in a PC. Contrary to popular belief however the CPU is not the big box which you plug your monitor into, but rather is just a chip about the size of a large postage stamp which slots into your motherboard and gets clamped down by a heatsink and fan (HSF) to keep it cool.

What is true though is that this thing does do most of the stuff when it comes to computing tasks so it's best not to skimp on this part. You need to consider what you'll be using your computer for, and how long it will be until your next CPU upgrade. If you just need an internet machine, with perhaps a bit of light gaming here and there, then any relatively decent dual core CPU should be fine. If you plan on using demanding applications, heavy gaming, or won't be upgrading for a long time, it may make more sense to purchase a faster running quad core CPU which may last you longer and be more future-proofed.

Which CPU you can use is dependant on what motherboard you'll be buying, so again let's break them down by socket...

Intel Socket 1366. Overall, these are the most expensive options and there are not a lot to choose from, but as these "Bloomfield" processors all share the same features at least you know what you're getting no matter which one you pick.

There are three chips in this family which are being marketed currently - the Core i7 920, 950, and 975 Extreme Edition, running at 2.66GHz, 3.06GHz and 3.33GHz respectively. All of them have four physical 'cores' (allowing the CPUs to work on more than one thing at a time) which each have two 'threads' (which further improve their multitasking ability). All of these Core i7 chips have 8MB of L3 cache (very high speed memory built right on the to chip itself to increase performance) and support Intel's Virtualization Technology if you're into that sort of thing.

These processors are king of the ring at the moment, offering the best performance in virtually all games and applications. Prices are reassuringly hefty at roughly $500, $1000 and $1800 for the three different models.

Intel Socket 1156 Also known as "Lynnfield" processors, these CPUs are slightly trimmed down versions of the Bloomfield chips for Socket 1366.

Available models are the Core i5 750, Core i7 860 and Core i7 870 running at 2.66GHz, 2.80GHz and 2.93GHz. Again they all have 4 physical cores but only the Core i7 860 and 870 are "hyperthreaded" with 2 threads per core. This shouldn't matter to most people however as not many applications or games can currently take advantage of the extra threads yet. They also offer the same 8MB L3 cache as the Socket 1366 CPUs.

For most users, the Core i5 750 will offer basically the same performance as its more expensive brethren so is a good choice for budget-conscious enthusiasts, priced at approximately $350. The two Core i7 chips go for about $500 and $1000 apiece.

Intel Socket 775 There are 2 families of chips worth paying attention to in this platform - Core 2 Duo and Pentium Dual Core - both of which provide great bang for buck. There are also Core 2 Quad chips available but they're almost as expensive as the much more powerful Core i5 750 mentioned above so they can pretty much be ignored now.

For around $200, the Core 2 Duo E7500 running at 2.93GHz will provide enough grunt for gaming and demanding applications without breaking the bank.

If you need to stretch your dollars even further, the 2.6GHz Pentium Dual Core E5300 will "do the job" for less than $120.

AMD Socket AM3. It's hard to recommend the AM3 platform when you're building a new PC because for about the same price you can get a more powerful Intel Lynnfield setup, but if you insist on sticking with AMD then you might as well get the fastest chip they produce which is the Phenom II X4 965 for around $345. With four cores running at 3.4GHz, this has the highest clock speed of any CPU currently on the market.

For a cheaper solution, or perhaps a SFF/HTPC setup there is also the 2.8GHz Athlon II X2 240 which can be had for under $100. Bargain! Just remember that using an AM3 CPU on an AM3 motherboard requires DDR3 RAM.

AMD Socket AM2/AM2+. One of the cool things about this socket is that it's compatible with AM3 CPUs (although you still have to use DDR2 RAM), so I am going to have to again recommend the 2.8GHz Athlon II X2 240 if you're after a budget performer.

If you after a bit more grunt (or just 2 more cores) but don't want to break the bank, then consider the 3.0GHz Phenom II X4 945. At $265, it is still definitely good value for money.

Other considerations

The one other thing you should really consider when it comes to CPUs it whether you'll be overclocking it or not. Almost all modern processors will let you squeeze 20% more clock speed out of them; many will run up to 50% faster; and some even more! You will however need to purchase an aftermarket heatsink and fan for this job as CPUs run hot when overclocked, and the stock cooler just won't cut it.

So that wraps things up for CPUs, stay tuned next week for the lowdown on arguably the most important part of a computer (for gamers at least) - the video card.