One normally thinks of a fan as a two wire device either plugged in, or not, on or off but that's not the case with modern computer fans Fans now have two wires to supply power, a third wire to provide control, and sometimes a fourth wire a sensor for actual fan speed PWM, pulse width modulation is a control signal generated on the motherboard to tell the fan or fans what to do, everything from off (no pulses) to full blast (max width pulses); this control signal is generated by firmware on a chip that receives temperature information from a number of sources the cpu, the gpu (sometimes) , the hdd, the memory and the ambient temperature on the motherboard as a whole my experience has been solely with laptops . If I were building a desktop computer from scratch I would have one two wire fan blowing all the time the computer was on and have the others all controlled by the chip on the motherboard as it sees fit The PWM hub merely provides a convenient place to plug multiple fans , whether they be simple two wire fans running all the time , or multiple wire fans controlled by the motherboard through the hub . My interpretation of cpu fan is the fan mounted on the cpu heatsink to force cooling air through it. I would not mess with that. There should be another socket on the mobo especially for the pwm fan hub Finally I would monitor all the temperature sensors and fan with a program like HWInfo for a while to ensure that I was getting the performance I had expected to get. ...T