A Central Processing Unit (CPU) is the main microchip in a computer, while a CPU fan is the dedicated fan that helps keep the processor cool. Processors generate heat from internal electrical energy. The more demand placed on a CPU, the harder it works, and the warmer it gets. If the CPU gets too warm it can make errors and eventually ‘melt’ becoming completely inoperable. A CPU fan works in conjunction with a heat sink to prevent this.
A heat sink is a metallic device that sits directly on the CPU, drawing heat away from the chip into its cooler, aluminum, fin-like structure. The CPU fan attaches to the heat sink, pulling air through the fins. By dissipating heat drawn into the heat sink, the fan indirectly cools the processor.
A CPU fan can come in a variety of sizes and is normally sold with a copper and/or aluminum heat sink. Specifications include diameter and whether the CPU fan uses ball bearings, thought to be quieter than non-bearing fans. The fan and heat sink will also indicate which processors it is compatible with, or rated to cool.
Processors that are sold with a heat sink and CPU fan normally carry a 5-year warranty, while those sold without commonly (but not always) carry a warranty of one year. While the processors might be identical, manufacturers know that inadequate cooling can drastically shorten the life of a CPU. In the case of a CPU sold without a heat sink and fan, the manufacturer has no guarantee that a customer will provide proper cooling.
Overclockers are computer enthusiasts that push CPUs, making them work faster than their marketed specifications. This causes the chips to run hotter than normal. Many overclockers prefer to provide their own advanced, aftermarket heat sinks and fans to protect overclocked CPUs. These heat sinks are normally taller than average, and the CPU fans are often more powerful while being quieter, adding less noise to the system than many commercial fans.