Editing Computer fan control (section)

== Fan connectors ==
The common cooling fans used in computers use standardized connectors with two to four pins. The first two pins are always used to deliver power to the fan motor, while the rest can be optional, depending on fan design and type:
* Ground{{snd}} common ground
* Vcc (Power){{snd}} nominally a +12&nbsp;V supply, though it may be variable depending on fan type and desired fan rotation speed
* Sense (or tachometer) output from fan{{snd}} outputs a signal that pulses twice for each revolution of the fan as a pulse train, with the signal frequency proportional to the fan speed
* Control input{{snd}} a [[pulse-width modulation]] (PWM) input signal, used when the cooling fan assembly has an internal motor driver circuit.  Fan assemblies with this control input provide the ability to adjust the rotational speed of the fan without changing the input voltage delivered to the cooling fan assembly. A variable rotation speed allows the cooling rate to be adjusted to meet demand, quietening the fan and saving energy when full speed is not required.

The color of the wires connected to these pins varies depending on the number of connectors, but the role of each pin is standardized and guaranteed to be the same on any system. Cooling fans equipped with either two- or three-pin connectors are usually designed to accept a wide range of input voltages, which directly affects the rotation speed of the blades.