'NC' means Not Connected, so the manufacturer didn't implement PWM control on those headers, presumably for cost-saving.

The SYSFAN headers can only control the fan speed via DC voltage, despite having a 4-pin fan header. The CPUFAN headers can control the fan speed via PWM signal or DC voltage (depending on the fan and which control method you select in the BIOS). So pay extra attention to that.īut that's easy to notice in the BIOS - when you just can't control a certain 4-pin fan with a PWM signal and instead only have DC (voltage) control available. Some motherboard models may only allow DC control for some of the fan headers, even though they can all be 4-pin headers. So for each fan, you have to select the right fan control method: DC for a 3-pin fan or PWM for a 4-pin fan. Side note: The 'RPM Speed Signal' pin (rotations per minute) in the picture is telling the motherboard at which speed the fan is spinning, it is not controlling the fan. With a PWM-controlled fan, the board powers it with a steady 12V, and the fan speed is controlled through the fourth pin via a PWM signal.

With a DC-controlled fan, the fan speed is regulated by the board powering it with lower or higher voltages (say, between 3V and 12V) instead of steady 12V. A 4-pin plug means it's PWM (pulse width modulation) controlled.

A three-pin plug means the fan is DC (= direct current) voltage-controlled.

Msi gaming laptop fan control