The Tyan Opteron mobo I got last summer has 4-pin headers for the CPU fans. I'm pretty sure they're the same as the ones described above. I've never actually seen a fan to plug into them (they are ...

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 ...

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 ...