A complex instruction set computer (CISC ) is a
computer architecture
In computer engineering, computer architecture is a description of the structure of a computer system made from component parts. It can sometimes be a high-level description that ignores details of the implementation. At a more detailed level, the ...
in which single
instructions can execute several low-level operations (such as a load from
memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered ...
, an
arithmetic operation
Operation or Operations may refer to:
Arts, entertainment and media
* ''Operation'' (game), a battery-operated board game that challenges dexterity
* Operation (music), a term used in musical set theory
* ''Operations'' (magazine), Multi-Man ...
, and a
memory store) or are capable of multi-step operations or
addressing modes within single instructions. The term was retroactively coined in contrast to
reduced instruction set computer (RISC)
and has therefore become something of an
umbrella term
In linguistics, semantics, general semantics, and ontologies, hyponymy () is a semantic relation between a hyponym denoting a subtype and a hypernym or hyperonym (sometimes called umbrella term or blanket term) denoting a supertype. In other ...
for everything that is not RISC, where the typical differentiating characteristic is that most RISC designs use uniform instruction length for almost all instructions, and employ strictly separate load and store instructions.
Examples of CISC architectures include complex
mainframe computers to simplistic microcontrollers where memory load and store operations are not separated from arithmetic instructions. Specific instruction set architectures that have been retroactively labeled CISC are