Why 4 header PWM on motherboards?

[mattyc]

I dont quite understand motherboard manufacturers reasons why the cpu fan header on 99.9% of motherboards is 4 pins. There are hardly any PWM fans available on the market, 99.9% of fans attached to aftermarket heatsinks are 3 pins not 4 and most motherboards cannot undervolt the 4 pin cpu header for a 3 pin fan so i just dont understand the logic behind this OR have i missed something?

[nutball]

so i just dont understand the logic behind this OR have i missed something?

99.9% of stock heatsink fans are 4-pin, 99.9% of people use the stock heatsink.

(oh and 99.9% of statistics are made up )

[ascl]

most motherboards cannot undervolt the 4 pin cpu header for a 3 pin fan

I don't agree with this.... or I have been exceptionally lucky with my motherboard choice. Its the one fan header that 99.9% of the time you can control!

[Klusu]

Lucky, yes.
Motherboards are cheaper. To adjust a 3-pin fan, the MB must convert the excess power into heat.
But the main goal is to make people buy new fans.

[DaveLessnau]

I'm using the Nexus PWM Series D12SL-12PWM 120mm Case Fan in one of my computers (open shoulders and all). I'm very happy with it.

http://www.newegg.com/Product/Product.a ... 6835610003

[Mr Evil]

4-pin fans should be quieter, and the tachometer can be read accurately at all speeds. It doesn't matter if 4-pin fans are not widely available retail, because most users don't buy fans, they use what comes with the PC. More will be available in the future though, as happens with any new standard.

Lucky, yes.
Motherboards are cheaper. To adjust a 3-pin fan, the MB must convert the excess power into heat.
But the main goal is to make people buy new fans.

As far as I know, all motherboards control 3-pin fan speed by PWM (modulation of the power supply, not a separate modulated control signal like the 4-pin fans), which is approximately 100% efficient.

[mattyc]

I'm using the Nexus PWM Series D12SL-12PWM 120mm Case Fan in one of my computers (open shoulders and all). I'm very happy with it.

http://www.newegg.com/Product/Product.a ... 6835610003

I have just ordered one of these so shall let you know how i get on. With 2000RPM it should keep my overclocked i7 nice and cool!

[Klusu]

As far as I know...

How do you know? Have you checked one MB?
Why 4-pin should be quieter? On the contrary, people complain about PWM noise...
Edit:
My P5K Premium adjusts chassis fan DC, not PWM. Does not adjust 3pin cpu fan.
An example of PWM noise: Glacialtech SilentBlade GT12025-LWD0A.
The way the PWM is implemented... probably just a mosfet, switching +12V to the motor on/off, driven directly by the 4th wire.
Anyway, PWM can not be quieter than a DC regulated fan.

[Mr Evil]

As far as I know...

How do you know? Have you checked one MB?
Why 4-pin should be quieter? On the contrary, people complain about PWM noise...

All the motherboards I have checked have use PWM (maybe half a dozen). I have seen quite a few others report similar findings. It would be strange to do it any other way because PWM is so efficient and so easy to implement.

I know a number of current 4-pin fans are reportedly noisy, but there aren't many examples yet, so I expect quieter ones to pop up eventually. They should be quieter because each fan can implement speed control in a way that best suits its motor. A fan could even use linear voltage control set by the PWM signal, if the manufacturer so desired.

[Hypernova]

PWM signal control makes the power circuit on the MB side easier. There is also the advantage of have lower power pwm signal instead of high power PWM modulated 12V near the area since the headers often are close to RAM VRMs. This reduces electrical interference.

[Darth Santa Fe]

I use a 92mm Scythe 4-pin PWM fan on my CNPS9500 heatsink. No cool LEDs, but it's quieter than Zalman's fan, and I can let the motherboard control the speed when things get warm.