Enough power for your needs. If you plan to use your computer to work with images or video, you'll need a CPU that is capable of serious number crunching. On the other hand, if you only want a word processor, a more modest CPU will suffice.

The type of processor -- Pentium or AMD -- that suits your needs. While both acquire very high ratings from popular vendors and testors, it really comes down to preference. Everyone experiences their own issues with each type of processor. Functionally, they compare. Price-wise - well, you'll see.

A processor that suits the system. Pay attention to the details of the overall computer system. Shelling out big bucks for a powerhouse CPU is only worthwhile if your motherboard can take advantage of the chip's muscle. The same is true of upgrade, or "overdrive," CPU chips, which adapt a lesser chip to higher performance: Don't waste your money by buying a Pentium overdrive chip for a motherboard that can't take advantage of the processor's power. For example, a computer with a PentiumI processor probably has a data bus that's too slow to get the most out of a faster CPU. Fast processors may also produce more heat than an older computer can handle. You're better off replacing the whole motherboard.

Marketing games. Be aware of confusing naming conventions. For example, Intel gave its speedy Pentium CPU a name -- rather than a number -- so it could secure a trademark. Other makers' "586" or "686" or "K6" processors are compatible with the Pentium but have different levels of processing power. And Intel itself now offers four flavors of Pentium:

The relationship between power and price. Is it worth an extra $100 for a chip that's 25 megahertz faster? Not always. It's more important to assess how much difference an upgrade will make for your intended use (sophisticated graphics work? simple word processing?) and what it's worth to you. Generally speaking, you’ll get the best value for your money with a processor that’s one step below the fastest that a manufacturer offers.