The Central Processing unit (also referred to as CPU) is 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 logic unit (ALU), hardware 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 sometimes 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 or "cores" 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.
History at Apple
The Apple I and Apple II were based on 8-bit MOS 6502 processors, which were sufficiently powerful at the time for low cost. Apple later switched to licensed designs from other manufacturers, such as Synertek.
The Apple Lisa used 68k processors from Motorola, which drastically improved performance through 16-bit/24-bit architecture. The Motorola CPUs were also used in early Macintosh models that transitioned to 32-bit-clean architecture used in the Macintosh Quadra series.
- Today in Apple history: Power Mac 7100 lands Apple in hot water with Carl Sagan by Luke Dormehl, Cult of Mac. 2020-03-14.
- Live from WWDC: Steve Jobs keynote by Peter Rojas, Engadget. 2005-06-06.
- WWDC Special Event — June 22 by Apple, YouTube. 2020-06-22.