Once you've determined the type of desktop system you want, a compact PC, a budget system, a mainstream all-purpose model, or a performance crackerjack, you need to know what components to look for. The processor and graphics chip you choose will determine many of your machine's capabilities, as will the system's memory and hard drive. Understanding those components will help you get the performance you need, without paying for things you don't.

You'll also want to consider details like the layout of the case, which can also make the difference between a pleasant workstation and a nightmare PC.

Processor

The CPU is one of your PC's most important components. The processor you choose is likely to determine your PC's shape and size, and will definitely determine its price. Generally, the higher the CPU clock speed, the faster the performance you may see, and the higher the price. A 3.46GHz Core i5-670 PC will trounce a 2.93GHz Core i3-530 system, but you'll pay nearly twice as much for the faster CPU. Another spec to watch is cache size: More is better, here: Core i3 and Core i5 parts have 4MB caches, while performance geared Core i7 chips have 6MB or 8MB caches.

Compact PCs and some all-in-ones use relatively puny netbook or notebook processors. Though these CPUs deliver weaker performance than desktop processors, they're also smaller and generate less heat, which makes them ideal for small machines. A PC packing an Atom processor should be fine for basic word processing, web surfing, and limited media playback, but little more.

ClarkdaleIntel's new Clarkdale line of Core i3 and Core i5 desktop processors tend to appear on systems in the budget desktop and mainstream desktop PC categories. Most users will find something they like in the Core i3 and Core i5 lines, as these CPUs offer dual core performance at palatable price points. Core i3 chips are the cheaper, lower powered models, so you'll generally find them in cheaper machines.

The quad core Core i7 targets users who need a real workhorse processor. If you play highend games or edit hours of audio or video, you'll benefit from the Core i7. The lowliest Core i3 CPU can easily handle basic computing tasks, so stay within a reasonable price range when possible. At the lowest end are dual core Pentium and Celeron processors. These chips appear in budget PCs, where price tags starting at £300 compensate for weaker performance.

Desktop PCs use either Intel or AMD processors. Intel currently holds the performance crown, but AMD has priced its dual- and quad-core chips aggressively. If you're looking for quad-core performance on a budget, AMD-based offerings are certainly worth a look.