Computer fan
Some ATX tower cases have one or more additional vents and mounting points in the left side panel where one or more fans may be installed to blow cool air directly onto the motherboard components and expansion cards, which are among the largest heat sources.
Air filters are often used over intake fans, to prevent dust from entering the case and clogging up the internal components.
Some of the higher powered cards can produce more heat than the CPU (dissipating up to 350 watts[4]), so effective cooling is especially important.
Used to cool the heatsink of the northbridge of a motherboard's chipset; this may be needed where the system bus is significantly overclocked and dissipates more power than as usual, but may otherwise be unnecessary.
Hard drives can produce considerable heat over time, and are heat-sensitive components that should not operate at excessive temperatures.
In rack-mounted servers, a single row of fans may operate to create an airflow through the chassis from front to rear, which is directed by passive ducts or shrouds across individual components' heat sinks.
[7] Two important functional specifications are the airflow that can be moved, typically stated in cubic feet per minute (CFM), and static pressure.
[8] Given in decibels, the sound volume figure can be also very important for home and office computers; larger fans are generally quieter for the same CFM.
Larger fans are usually used for cooling case, CPUs with large heatsink and ATX power supply.
Smaller fans are usually used for cooling CPUs with small heatsink, SFX power supply, graphics cards, northbridges, etc.
The speed of rotation (specified in revolutions per minute, RPM) together with the static pressure determine the airflow for a given fan.
Fan lifetimes are usually quoted under the assumption of running at maximum speed and at a fixed ambient temperature.
Some improvement can be achieved by eliminating all fans except one in the power supply which also draws hot air out of the case.
[27] Systems can be designed to use passive cooling alone, reducing noise and eliminating moving parts that may fail.
