Complex instruction set computer
Processor with instructions capable of multi-step operations / From Wikipedia, the free encyclopedia
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A complex instruction set computer (CISC /ˈsɪsk/) is a computer architecture in which single instructions can execute several low-level operations (such as a load from memory, an arithmetic operation, and a memory store) or are capable of multi-step operations or addressing modes within single instructions.[citation needed] The term was retroactively coined in contrast to reduced instruction set computer (RISC)[1] and has therefore become something of an umbrella term for everything that is not RISC,[citation needed] where the typical differentiating characteristic[dubious – discuss] is that most RISC designs use uniform instruction length for almost all instructions, and employ strictly separate load and store instructions.
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Examples of CISC architectures include complex mainframe computers to simplistic microcontrollers where memory load and store operations are not separated from arithmetic instructions.[citation needed] Specific instruction set architectures that have been retroactively labeled CISC are System/360 through z/Architecture, the PDP-11 and VAX architectures, and many others. Well known microprocessors and microcontrollers that have also been labeled CISC in many academic publications[citation needed] include the Motorola 6800, 6809 and 68000 families; the Intel 8080, iAPX 432 and x86 family; the Zilog Z80, Z8 and Z8000 families; the National Semiconductor NS320xx family; the MOS Technology 6502 family; the Intel 8051 family; and others.
Some designs have been regarded as borderline cases by some writers.[who?] For instance, the Microchip Technology PIC has been labeled RISC in some circles and CISC in others.