3-pin vs. 4-pin CPU fans and PWM fan speed control

[jrichrds]

My old Asus slot1 motherboard could do PWM control through its 3-pin fan headers.

Now I see all new motherboards have 4-pin CPU fan headers, and that stock AMD/Intel coolers all have 4-pin CPU fans. The 4th pin is supposed to be for PWM fan speed control.

Problem is that the CPU coolers I'm interested in to replace my stock cooler have the 3-pin fan header rather than 4-pin. But for pure simplicity, I love the ability to allow the BIOS to control my CPU fan speed...no need for hardware accessories or software programs to keep the fan speed and noise where I want it.

So I have 2 questions:
1) Has anyone had luck retaining BIOS CPU fan speed control (without having to use a software program) using a 3-pin fan on the 4-pin CPU fan header?

2) Why is that 4th pin even required when motherboards have been doing PWM fan speed control with 3-pin fan headers for years prior to the introduction of the 4th pin?

 

[aigomorla]

4th pin is for pwm design fans.

and yes you can use a 3 pin fan on a 4pin header.
There setup so you can only plug the correct 3 that fits.


And i cant answer your first question as i dont use my mobo headers. All my fans are on controllers. :T

 

[VirtualLarry]

You can control the 3-pin fans (RPM sensing only, no PWM control), using voltage control. Some mobos support this, it's usually a BIOS option.

 

[GundamF91]

Yes, you can use 3pin, but there are some issues with speed control.

 

[WobbleWobble]

My Gigabyte EP35-DS3R BIOS doesn't control fan speed with a 3-pin fan, only a 4-pin PWM fan. I've tried. The fan will work at full speed though.

 

[nevbie]

My ASUS P5K-E/wifi board has 1 CPU fan plug and 3 or 4 case fan plugs. The CPU fan plug is 4pin PWM and the other plugs are 3pin.

The BIOS offers some kind of PWM control for the fan plugged in CPU fan power plug, and a voltage based control for the others.

Both my fans are 3pin (scythe s-flex E) and I plugged them to the case plugs, even the CPU fan. The voltage based control (one setting for all fan plugs of the same type) works flawlessly and I basically set all fans to run a bit slower (fans rated 1200rpm running 811rpm). Chassis fan control options are auto, 90%, 80%, 70% and 60%. BIOS supposedly adjusts the speed if NB temperature gets too hot (or whatever sensor), and I can roughly select the triggering temperature. The rpm doesn't really ever change from ~811.

I haven't tried the PWM-based control yet, as the voltage-based options seem to allow me more manual control.

 

[VirtualLarry]

Originally posted by: WobbleWobble
My Gigabyte EP35-DS3R BIOS doesn't control fan speed with a 3-pin fan, only a 4-pin PWM fan. I've tried. The fan will work at full speed though.

Really? That's surprising. I have a P35-DS3R rev 1, and it does have both PWM and "legacy" fan-control modes.