c.p.u.

 The central processing unit, that part of the electronic circuitry of a computer in which the arithmetic and logical operations are performed on input data, which are thereby converted to output data; it is usually located on the mainboard, or motherboard, of a computer. The CPU and the memory form the central part of a computer to which the peripherals are attached. Most personal computers as of 1998 had only one CPU, but some computers may have more than one CPU.  [WordNet 1.5]