Computer fan

Six 80 mm fans, commonplace components in earlier personal computers (either as a pair or mixed with fans of other sizes)
A 30-millimetre (1.2 in) PC fan in a square black plastic chassis lying on the hub of a circular one of translucent plastic sized 250 mm (9.8 in)

A computer fan is any fan inside, or attached to, a computer case used for active cooling. 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. Both axial and sometimes centrifugal (blower/squirrel-cage) fans are used in computers. Computer fans commonly come in standard sizes, such as 92 mm, 120 mm (most common), 140 mm, and even 200–220 mm. Computer fans are powered and controlled using 3-pin or 4-pin fan connectors.