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 card 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. (Our holiday buying guide includes further shopping tips for purchasing a desktop PC.)
You'll also want to consider details like the layout of the case, which can make the difference between a pleasant workstation and a nightmare PC.
The CPU is one of your PC's most important components. The processor you choose is likely to have a major impact on your PC's shape and size, and it will definitely influence its price. Generally, the higher the CPU clock speed, the faster the performance you may see--and the higher the price. A 3.4GHz Core i7-2600 PC will trounce a 3.10 GHz Core i3-2100 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 parts have 4MB caches, Core i5 parts have 6MB caches, and performance-geared Core i7 chips have 8MB caches.
Compact PCs and some all-in-ones use relatively puny netbook or laptop processors. Though these CPUs deliver weaker performance than desktop processors do, they're also smaller and generate less heat, which makes them ideal for small machines. A PC packing an Intel Atom or AMD Fusion processor should be fine for basic word processing, Web surfing, and limited media playback--but little more.
Intel's new Sandy Bridge line of desktop processors run the gamut from Budget PCs to Performance PCs. Most users will find something they like in the Core i3 and Core i5 lines, as these CPUs offer dual-core performance at palatable prices. Core i3 chips are the cheaper, lower-powered models, so you'll generally find them in less expensive machines.
The quad- and six-core Core i7 targets users who need a workhorse processor. If you play high-end 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.
Desktop PCs use either Intel or AMD processors. Intel currently holds the performance crown, but AMD has priced its new quad- and six-core chips aggressively. If you're looking for multicore performance on a budget, AMD-based offerings are certainly worth checking out.
The GPU (graphics processing unit) is responsible for everything you see on your display, whether you play games, watch videos, or just stare at the Aero desktop baked into Windows 7.
If you aren't interested in gaming on your PC, integrated graphics built onto the motherboard--or in the CPU itself--are the way to go. Integrated graphics help keep a system's cost low, and they deliver enough power to run simple games or high-definition Flash video.
If you plan to render your own high-definition content or to play Skyrim, you'll need a discrete graphics card. Such cards, which come installed in a PCIe x16 slot on your motherboard, deliver significantly more power than integrated graphics do. Both AMD and Nvidia offer plenty of options to choose from.
Variables such as power consumption, size, and the brand of your motherboard (which may limit which cards you can use) will help determine the GPU that's right for you. Gamers with deep pockets can opt for a multiple-graphics-card setup using either Nvidia's SLI or AMD's CrossFire technology, either of which sets multiple cards to work in tandem for vastly improved performance. For buying options, check out our "Top-Rated Graphics Cards."