complex instruction set computer (CISC)

The CISC architecture, Complex Instruction Set Computer (CISC), is a processor architecture with an extensive and complex instruction set. Due to the historical development of computers and the memories used in them, recurring instruction sequences were combined into complex instructions in the computers of the second generation.

This development was related to the relatively slow access times to the memory units. In addition, memory was relatively expensive and programs were therefore expected to occupy extremely little memory. This led to the fact that the programs were short, written in machine language were not stored in the main memory but as microprograms in a faster Read Only Memory( ROM).

Many Intel processors were built in CISC architecture, including the classic 80xx family processors such as the 80386 and 80486 and from Motorola the 6800 and 68000.

In contrast to the CISC architecture is the RISC architecture, Reduced Instruction Set Computer (RISC), which works with a reduced instruction set and is therefore considerably faster.