Processor Kinds

Kinds of Processors

Processors can broadly be divided into the categories of: CISC, RISC, hybrid, and special purpose.

Complex Instruction Set Computers (CISC) have a large instruction set, with hardware support for a wide variety of operations. In scientific, engineering, and mathematical operations with hand coded assembly language (and some business applications with hand coded assembly language), CISC processors usually perform the most work in the shortest time.

Reduced Instruction Set Computers (RISC) have a small, compact instruction set. In most business applications and in programs created by compilers from high level language source, RISC processors usually perform the most work in the shortest time.

Hybrid processors are some combination of CISC and RISC approaches, attempting to balance the advantages of each approach.

Special purpose processors are optimized to perform specific functions. Digital signal processors and various kinds of co-processors are the most common kinds of special purpose processors.

Hypothetical processors are processors that don’t exist yet (and may never exist). Sometimes these are processors in the design phase. Sometimes these are processors used for theoretical work. The most famous hypothetical processor is MIX (or 1009), a hypothetical teaching processor created by Donald E. Knuth for presenting computer algorithms in his famous series “The Art of Computer Programming” (discussed in the Basic Concepts section of Volume I, Fundamental Algorithms).