Acronym for Central Processing Unit.

The bit of the computer that does all the execution of commands.

There are several different arch's that Linux supports, including (but not exclusively):

Other CPU families include:

CPUs come in 2 flavours: RISC and CISC, although the lines between the 2 are not clear-cut as they should be in theory...

See CPUSockets for cpu fittings onto motherboards, and MotherboardMonitoring for checking the current temperature of your CPU (under linux).