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CISC (Complex Instruction Set Computer)
Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.
Computer processors contain instructions or microcode to carry out various functions. The richer the instruction set, the easier it is to write programs for the microprocessor, but a rich set of microcode can affect performance. This trade-off differentiates the two categories of microprocessors:
RISC designs are based on work performed at IBM by John Cocke, who found that about 20 percent of a computer's instructions did about 80 percent of the work. Thus, RISC-designed systems are generally faster than CISC systems. His 80/20 rule spawned the development of RISC architecture.
Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.