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3-pin fan vs. 4-pin fan

Last response: in Motherboards
July 20, 2011 5:12:43 AM

I have new motherboard that has a 4-pin fan header:
+5V, Fan In, Fan PWR, GND

But all the case fans I have are 3-pin. The 3-pin female plug fits on the 4-pin motherboard fan header, but without connecting the +5V.

What's the difference between the 4-pin and 3-pin fans and do you lose anything from connecting a 3-pin fan to a 4-pin header?

More about : pin fan pin fan

a c 156 V Motherboard
July 20, 2011 11:52:53 AM

No. The 3 pin fans allow the motherboard to monitor the speed of the fan. The fourth line on a 4 pin fan allows the motherboard to control the fan.

The connectors of both are keyed so that you cannot plug a 3 pin fan into a 4 pin motherboard connector wrong.
July 20, 2011 12:04:33 PM

Why is the 4th pin labeled as "+5V"? To me, that says that it's some sort of power pin that stays at +5V forever. How does this allow the CPU to control the fan? Does it "pulsate" at +5V "square wave" or something like that to control the speed of the fan?