(Central Processing Unit) The computing part of the computer. Also called the "processor," it is made up of the control unit and ALU. Today, the CPUs of almost all computers are contained on a single chip.|
The CPU, clock and main memory make up a computer. A complete computer system requires the addition of control units, input, output and storage devices and an operating system.
From the Mainframe Point of View
Computer professionals involved with mainframes and minicomputers often refer to the whole computer as the CPU, in which case, CPU refers to the processor, memory (RAM) and I/O architecture (channels or buses).
Depending on which end of the field you are in, a CPU can mean the processor, memory and everything inside the cabinet, or just the microprocessor itself.