central processing unit
(CPU, processor) The part of a computer which controls all the other parts. Designs vary widely but the CPU generally consists of the control unit, the arithmetic and logic unit (ALU), registers, temporary buffers and various other logic.
The control unit fetches instructions from memory and decodes them to produce signals which control the other parts of the computer. These signals cause it to transfer data between memory and ALU or to activate peripherals to perform input or output.
Various types of memory, including cache, RAM and ROM, are often considered to be part of the CPU, particularly in modern microprocessors where a single integrated circuit may contain one or more processors as well as any or all of the above types of memory. The CPU, and any of these components that are in separate chips, are usually all located on the same printed circuit board, known as the motherboard. This in turn is located in the system unit (sometimes incorrectly referred to as the "CPU").
A parallel computer has several CPUs which may share other resources such as memory and peripherals.
The term "processor" has to some extent replaced "CPU", though RAM and ROM are not logically part of the processor.