The Collaborative International Dictionary of English v.0.48:

CPU \CPU\, cpu \c.p.u.\n. abbr.
   1. (Computers) 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. [acronym]

   Syn: central processing unit, CPU, C.P.U., central processor,
        processor.
        [WordNet 1.5 +PJC]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

CPU
       Central Processing Unit