When electricity runs through a circuit, it produces heat. Heat is dangerous to computer components, so parts which get particularly hot use heat sinks to dissipate the heat that they create. Generally, the central processing unit (CPU), the main chip that runs a personal computer, is the most likely part to require a heat sink. Some graphics cards also use their own heat sinks to dissipate heat, particularly if they are very powerful.
Heat sinks are made of a metal that conducts heat very well, usually copper. When one section of the heat sink is in contact with something very hot, the CPU or graphic processing chip, the heat sink absorbs the heat from the chip. The heat is spread through the metal of the heat sink and dissipates into the air. Most heat sinks have a fan attached, which moves air across the heat sink, making the cooling more efficient.
Heat sinks are attached to the CPU or graphic card by plastic and metal clips. These clips keep the entire heat sink snugly in place. If the heat sink ever comes off while the computer is running, it is only a matter of a few seconds before the processor will become so hot that it will be ruined. It is very important never to start a computer without a properly mounted heat sink.
In order to ensure that the heat sink is in constant contact with the processor, a layer of conductive grease or glue is usually added. This grease or glue conducts heat very well, and makes sure that no air comes between the heat sink and the CPU. Air is a relatively poor heat conductor, so it will not cool the CPU efficiently enough to prevent damage.
Heat sinks come in many different shapes and sizes. Experts disagree about the exact size and configuration which produces the best results. Some computer users prefer rounded heat sinks with open centers like a tube, and a fan which pulls the air through the fins of the heat sink and out the top. Another common design is a cube shaped heat sink, with many thin fingers of metal, and a fan which blows the air down over the heat sink.
The important factors are that the heat sink has a lot of surface area, that it is secure, and that it has adequate air flow. The fins or fingers of metal provide heat sinks with more surface area for the heat to escape from. The grease or glue, along with the clips, keep the heat sink in constant and secure contact with the CPU. The fan makes sure that air keeps flowing, either by pulling it up or by pushing it down over the heat sink. Regardless of the size, shape or style of heat sinks, they all perform the crucial job of keeping vulnerable computer components from overheating with use.