Case fans may be placed as intake fans, drawing cooler outside air in through the front or bottom of the chassis (where it may also be drawn over the internal hard drive racks), or exhaust fans, expelling warm air through the top or rear. The components inside the case cannot dissipate heat efficiently if the surrounding air is too hot. Applications įans are used to move air through the computer case. Chassis or case fans, usually one exhaust fan to expel heated air from the rear and optionally an intake fan to draw cooler air in through the front, became common with the arrival of the Pentium 4 in late 2000. Active cooling on CPUs started to appear on the Intel 80486, and by 1997 was standard on all desktop processors.

In the IBM PC compatible market, the computer's power supply unit (PSU) almost always uses an exhaust fan to expel warm air from the PSU. A user can even supplement this function with additional cooling components or connect a manual fan controller with knobs that set fans to different speeds. A computer's BIOS can control the speed of the built-in fan system for the computer.

Fan control is not always an automatic process. Fans attached to components are usually used in combination with a heat sink to increase the area of heated surface in contact with the air, thereby improving the efficiency of cooling. To cool these components, fans are used to move heated air away from the components and draw cooler air over them. While in earlier personal computers it was possible to cool most components using natural convection ( passive cooling), many modern components require more effective active cooling. Computer fans are powered and controlled using 3-pin or 4-pin fan connectors. Computer fans commonly come in standard sizes, such as 92 mm, 120 mm (most common), 140 mm, and even 200–220 mm.

Both axial and sometimes centrifugal (blower/squirrel-cage) fans are used in computers. Fans are used to draw cooler air into the case from the outside, expel warm air from inside and move air across a heat sink to cool a particular component. A 30-millimetre (1.2 in) PC fan laying atop one sized 250 mm (9.8 in)Ī computer fan is any fan inside, or attached to, a computer case used for active cooling.

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