Detecting fan speed in BIOS

[yaddayadda]

I have just put in a new front fan on my case and was wondering how I get the BIOS to detect what rpm it is going at. The rear fan and processor fan speeds are detected, but the new front fan isn't. There wasn't one before, so do I have to enable something in the BIOS?

[Raptor]

Your mainboard may not be equipped with sensors for that particulair fan.