What's the difference between PWM and "auto" fan control in BIOS?

[FusionFool]

Not sure if this is a standard distinction, I can't control the CPU fan (which has 4 pins and the system can control it under load) with Speedfan with either setting. FWIW I have the GA-M55SLI-S4 1.0 with the Beta F11j BIOS.

[Vinster]

PWM is the most sure way of confirming fan speed rotation. if that fan is commanded at 1500rpm and the MB senses that the fan is spinning at 1450rpm it will compensate the difference, increase the voltage and make it 1500RPM. possibly with your MB being set to Auto is disabling the control from windows?

in your MB, Auto sets the follwing; BIOS autodetects the type of CPU fan you installed and sets the optimal CPU Smart FAN control mode for it. (Default Value)

But for this to operate properly you also have to enable CPU Smart FAN Control, and your CPU has to support it.

I would try to disable CPU Smart Fan and then set the fan control to PWM and then see it you can control it in windows. only issue with that is if overclocking, you may not be adaquately cooling the system during bootup.

but it could be worth a try.

Vin