A lot of motherboards have one 4 pin header for the cpu and 3 pin headers for any other fans.
Cpu cooling fan 3 pin vs 4 pin.
Now 2 pin cooling fans have been less to use because the fan of 2 pin cannot meet the requirements in terms of shifting etc in contrast 3 pin 4 pin fan is the main stream now.
They use variable voltage speed control.
I wouldn t be surprised if everything moved to 4 pin eventually but we re still in the early stages.
Any option can be made to work though.
The 3 connector fan is very common use in laptop it can adjust the fan speed according to the cpu.
For custom cooling usually the pump is contrlled by the motherboard cpu fan header 4 pin and the radiator fans are controlled either by the case fan 3 pin motherboard headers or by a module eg corsair h100i.
If your motherboard has a 4 pin header for the cpu fan i d look for a 4 pin fan for the best control.
I finally replaced my cpu fan from a 3 pin to a 4 pin connector to hear the difference in sound.
You use 3 pin fans for case fans.