Once you have the opportunity to start looking inside multiple computer cases, you may notice that some CPU cooling fans have an extra wire compared to others. What is the difference between three and four wire fans? Today’s SuperUser Q&A post has the answer to a curious reader’s question.
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SuperUser reader RockPaperLizard wants to know what the difference is between three and four wire CPU fans:
What is the difference between three and four wire CPU cooling fans (besides the obvious answer of one wire)?
What is the difference between three and four wire CPU fans?
SuperUser contributor Homey_D_Clown_IT has the answer for us:
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’s 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 since it has the extra (fourth) wire used for controlling and sending signals 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 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.
A three wire fan connecting to a four pin fan header:
Note: When connecting a three wire fan to a four pin fan header, the fan is always on; there is no fan control.
A four wire fan connecting to a four pin fan header:
A four wire fan connecting to a three pin fan header:
Source: Three Wire and Four Wire Fan Connectors [Intel]
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