What controls the Sys_Fan PWM signal?

[haris262]

So I know that when it comes to the CPU 4-pin header the PWM signal is changed depending on the CPU's temperature. But there are more 4-pin fan headers on the motherboard which use PWM apart from the CPU dedicated ones. I have found that in most of them these are usually called Sys_Fan1, Sys_Fan2 etc. So this is my question: what controls the PWM signal on these fans? Is it the temperature of another component or is it something you can manually set up in the motherboard's bios? If I were to plug a 4 pin fan in one of those headers, what would it take for the PWM signal to change?

The pic below has 3 of these "extra" 4-pin fan headers

Thank you for the help!

 

[ingtar33]

depends on the motherboard. On my asus maximus gene VI, it simply polls the hottest reported temp on the motherboard, and decides the fan speed from that. of course i can built fan profiles on it that fit my usage, so right now, when i'm not really doing anything on my pc, my case fans aren't spinning at all because the warmest part on the motherboard is 45C, while the cpu fan is spinning at it's min - 600RPM