Winn L. Rosch Hardware Bible, Sixth Edition

Cooling

A case can be confining. It can keep just about everything from escaping, including the heat that electronic circuits produce as a by-product of performing their normal functions. Some of the electricity in any circuit (except one made from superconductors) is turned into heat by the unavoidable electrical resistance of the circuit. Heat is also generated whenever an element of a computer circuit changes state. In fact, nearly all the electricity consumed by a computer eventually turns into heat.

Inside the protective (and confining) case of the computer, that heat builds up, thus driving up the temperature. Heat is the worst enemy of semiconductor circuits; it can shorten their lives considerably or even cause their catastrophic failure. ...