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Central Processing Unit (CPU): the brain inside a PC that processes data and dictates the power and price of a computer.

In the past year, CPU speeds have jumped from 600 MHz to 1 GHz. With speeds exceeding 1.5 GHz expected by year's end, the chip race rages on. But here's a tip: Your CPU's performance is determined by more than just the megahertz or gigahertz numbers touted in the vendors' advertisements. As chips speed up and applications demand more power, your need to understand what happens inside your CPU becomes greater than ever.

Here's what you should know:

• A CPU performs three basic tasks: It reads data, it manipulates data, and often it writes data to memory.
  
  
• Raw speed is measured in megahertz, but other features, such as design, are important in determining a chip's performance.
  
  
• The chip you'll want inside your PC depends on how much you're willing to spend and what you'll use the PC for.
  
  

Building Blocks

Before you understand how a CPU works, you should know what a CPU is made of. A CPU comprises millions of microscopic transistors etched by chemical and photolithographic processes into a polished sliver of silicon about the size of your thumbnail.

Those tiny transistors store electrical charges that correspond to ones or zeros, which make up the binary language computers use to communicate. Groups of transistors are linked to store values; they also perform logic and math, and with the help of a quartz crystal clock, they pace their functions like synchronized swimmers. In other words, they can process data.