Three-wire and four-wire CPU fans, what’s the difference

chassiscoolingcpufan

What is the difference between 3-Wire and 4-Wire CPU cooling fans?

Of course, the obvious answer is “1 Wire!” 🙂

Best Answer

Basic Differences

A three pin connector is basically power (5/12 volt), ground, and signal. The signal wire measures how fast the fan is moving without any controls for the fan speed. With this type, fan speed is typically controlled by increasing or decreasing the voltage over the power wire.

A four pin connector is a little different than the three pin connector as it has the extra [fourth] wire for control to send a signal to the fan which likely has a chip on it that tells it to slow down or speed up in addition to the other wires just as the three pin connector has.

Three Wire and Four Wire Fan Connectors

Chassis and processor fans use either a three-wire or four-wire connector. The three-wire connectors are for small chassis fans with lower power consumption. The four-wire connectors are for processor fans with higher power consumption.

Three-wire fan connecting to a four-pin fan header

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Fan header pinouts

  • Pin: 1

    • Three-wire fan support: Ground
  • Pin: 2

    • Three-wire fan support: 12 V
  • Pin: 3

    • Three-wire fan support: FAN_TACH
  • Pin: N/A

    • Three-wire fan support: N/A

Note: When connecting a three-wire fan to a four-pin fan header, the fan is always on; there is no fan control

Four-wire fan connecting to a four-pin fan header

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Four-wire fan connecting to a three-pin fan header

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  • Pin: 1

    • Three-wire fan support: Ground
  • Pin: 2

    • Three-wire fan support: 12 V
  • Pin: 3

    • Three-wire fan support: FAN_TACH
  • Pin: 4

    • Three-wire fan support: FAN_CONTROL

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