How does the motherboard know what RPM to spin a PWM fan at?

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Bojangle12

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Feb 10, 2014
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I have a Gigabyte GA-990FXA-UD3 motherboard. I can understand that the CPU fan will spin at higher RPM if the CPU is at a higher temperature. I'm sure the CPU manufacturer programs it into the processer, and maybe the chipsets.

But how does a PWM for Sys_fan1 know to make it spin faster? Does it somehow know it's location in the computer?

So can I plug in a PWM fan in the front intake in either PWM connector, and the computer knows how to make it spin faster?

 
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There are a couple of different temperature sensors on the MB, when those temperature sensors read a higher temperature they spin the fans faster.
The MB doesn't make any attempt to know where the individual fans are located, it just spins them all faster.

If you wanted more individual control there are a few software options that show each temperature sensor reading and all the fan data the MB had. Speedfan is the one I use on occasion to check temperatures.
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terryd75

terryd75

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Jan 15, 2012
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Yes,,,,, The mbod has control over those pwm ports, and will even send you the info on how fast they are running, etc. After hooking the fans up, go into your bios and you will see the fan speeds, etc.
 
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noahhicks

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Mar 29, 2014
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There are a couple of different temperature sensors on the MB, when those temperature sensors read a higher temperature they spin the fans faster.
The MB doesn't make any attempt to know where the individual fans are located, it just spins them all faster.

If you wanted more individual control there are a few software options that show each temperature sensor reading and all the fan data the MB had. Speedfan is the one I use on occasion to check temperatures.
 
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Solution
bryonhowley

bryonhowley

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Oct 24, 2011
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Well it depends on the placement of the temp sensors. For example plugging a fan into the CPU fan header will make that fan speed up or slow down depending on the temp of the sensor in that location. If the heat goes up the fan would speed up for the fan plugged into that header.
 
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Swordkd

Swordkd

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Oct 3, 2012
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No, the motherboard doesn't know the location of the case fans for your system. However, it does take temperature readings at different points on the motherboard, and increases the speed of any fans plugged into the sys_fan locations. That's why it's important to plug the cpu fan into the right header(cpu_fan), so it runs based off the correct information in regards to the cpu temp.
 
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