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 ...

The Balanced Technology Extended (BTX) interface specification was developed by Intel to provide standard interfaces and form factors in an effort to address the thermal and acoustical issues ...

Folks who shop for motherboards—whether as an upgrade component or for a build-a-PC-from-scratch project—are a savvy bunch, confident enough to take their PC to pieces and put it back together again.