IIRC the extra pin on a 4 pin motherboard header may report if the fan has totally stopped, like a failure line, to tell the mobo to shut the CPU off. I've got an old 4 pin fan here from a '94 vintage ...

I've been installing a few case fans onto my new PC, and I had a fan that connected via the three pins on the motherboard. I've moved the three pin fan to a new location but I can't find any other ...

CPU_FAN and CPU_OPT are entirely different and serve distinct purposes in the context of a computer cooling system. CPU_FAN or CPU Fan Header is the primary 4-pin fan header on a motherboard, and it ...