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system fan on MB... 4 pins... what?

post #1 of 5
Thread Starter 
Errr... lookin at my mb the other day.. Sys Fan has 4 pins... and this is the one no where near my cpu.... why 4 pins?
The heck do I use this?
post #2 of 5
You can just plug in a 3-pin fan to a 4-pin header, no problem smile.gif
Pretty much all the fan-headers on my motherboard are 4-pins.
Behemoth
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Behemoth
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post #3 of 5
Fourth pin is for PWM (Pulse with modulation) with which much better speed control could be had. It sends the pulses of 12v which could be of various frequencies and so control the speed of the motor. You could use a 3 pin fan on it but will not get a fine rpm control, if at all. Such a fan would run full speed all the time.
post #4 of 5
Quote:
Originally Posted by MishelLngelo View Post

Fourth pin is for PWM (Pulse with width modulation) with which much better speed control could be had.

TFTFY

Also correct about plugging in a 3 pin fan header. The PWM just defaults to 100%. IIRC most motherboard fan software will still allow you to do voltage control of the fan speed on the 4 pin header (someone confirm this maybe?)
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alt.sanity
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post #5 of 5
The PWM does not default to anything, it's just not there when you plug a 3 pin fan (or pump) in a 4pin on MB. However, some MBs do let you control it by voltage and some not. Software control can be achieved only when so enabled in BIOS.
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