# PWM Fan Speed Question



## Esa1996

Hi people,

In my BIOS I can set my CPU fan speed PWM to 0.75-2.5. What's the difference? I assume that the higher the PWM number is the faster the fans spin on average. Am I right?


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## Currency

If I'm not mistaken that should be your fans voltage, increasing it would make them spin faster. When dealing with PWM fans, your forth pin on the fan header is one telling your bios the fan speeds. if your running three pin fans they shouldn't be affected by any changes. 

correct me if I am mistaken, been reading up on PWM's as I'm debating on a fan controller as I have seven fans right now.


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## Esa1996

Seems to be correct. My CPU temperature in idle drops by about 5C when I put the PWM to 2.5


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## bomberboysk

Correct, with a 4 pin fan the additional pin is a pulse width modulation signal. 3 pin would have Common, +12V, and a Tach signal, while 2 pin would be +12V and Common only. 

On your particular board, the 0.75 and 2.5 are (somewhat) arbitrary values for something Gigabyte refers to as "PWM Value/ degree C". Depending on the hardware, there are so many "steps" to the PWM control, (eg. 0 - 127), and each degree C that the cpu temperature increases, that value will bump up by 2.5 steps until at maximum speed. It used to be that you could also set the starting PWM Value, which I believe they have removed that from some of their boards, which doesn't help users unfamiliar with those boards to understand it's functionality.

However, some boards have the functionality of PWM control on the +12v signal, which negates the need to utilize a 4pin fan for RPM control.


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