3-pin fan vs. 4-pin fan

[rasmasyean]

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?

 

[jsc]

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.

 

[rasmasyean]

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?

 

[JonnyDough]

http://www.intel.com/support/motherboards/desktop/sb/cs-012074.htm