so i CAN plug the 3 pin cpu fan to my 4 pin motherboard header? what is the extra pin there for then?
Yes,you can connect a 3 pin cpu fan to a 4 pin motherboard header.The fourth pin is for PWM. The PWM fan has the extra fourth pin, on which is sent a PWM control signal. The fan does the real work of reducing speed. They will work as normal 3-pin fans when reduced by linear voltage control.