I’ve got a whole bunch of fancy Noctua PWM fans in my PC I want to control the speed of. How do I boss them around? The most authoritative source of how these fans communicate is from an Intel specification. Even better is a whitepaper by Noctua themselves that describes every detail you could ever want to know.

Cos numbering pins is for suckas
Okay so at least we aren’t going to be reverse engineering these fans. What exactly do they want on that PWM input pin?