I found this floating around menorcabytes's DB backup thought it might prove useful to someone.

The computer’s brain is a chunk of silicon buried deep inside the computer’s case. Over the years, the CPU has grown from the size of a cracker to a mammoth chocolate bar. This computer chip is the microprocessor, but nerds tend to call it a central processing unit, or CPU.

The computer’s microprocessor determines how quickly and powerfully the computer can toss information around. Windows XP isn’t happy unless it rides on a Pentium III microprocessor or an even faster one. You can also use Intel’s speedier Pentium 4 and Itanium microprocessors, as well as a speedy AMD Athlon. Yep, if you’re looking to use Windows XP, you’ll probably want a new computer. microprocessor is the current evolution of the gadget that powered those little 1970s pocket calculators. It performs all the computer’s background calculations, from juggling spreadsheets to swapping dirty jokes through office e-mail.

Microprocessors are described by several numbers. Generally, the bigger the numbers, the faster and more powerful the chip. Don’t know what microprocessor lives inside your computer? Right-click on the Start menu’s My Computer button and choose Properties from the pop-up menu. When the System Proper ties window appears, the processor’s name appears near the bottom. If the numbers still look confusing, Intel offers free software to identify your Intel CPU at www.inte.coml.

Don’t be afraid to buy a fast AMD Athlon microprocessor for your new computer. It’s just as fast, cheaper, and just as good as Intel’s.

A CPU manufacturers assign several numbers to their chips. Intel usually places a number after the chip’s name: Pentium II, Pentium III, and Pentium 4. A CPU’s processing speed is measured in mega- hertz, or MHz. The cache size (pronounced “cash”) is measured in kilobytes, like 512K. When comparing microprocessors, just remember that the bigger the number, the faster Windows per- forms.

(Taken from: Windows XP For Dummies, 2nd Edition - Andy Rathbone (2001))