CPU – Most of the mathematical manipulations that make computers operate are done by the CPU. Other components like high performance graphic cards, may also have their own processors, but their results still have to be passed through the CPU. The speed of the computer is usually measured by the speed of the CPU. Even though other factors also affect overall speed, the CPU rating is generally seen as the single most important measure of performance. For instance, 3-D computer games would run better on a computer with a higher CPU rating than a computer used mostly for office applications that have a lower CPU rating. CPU in most computers today, are usually rated between 2.0 GHz and 3.0 GHz allowing for a wider range of computer programs from computer games to movies. This measurement refer to the number of calculations the processor can make in 1 second. The higher the number, the faster (better) the computer. CPUs generate a lot of heat doing this work, so they need a heat sink and fan attached to them