Reduced Instruction Set Computer

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Related to reduced instruction set computing: complex instruction set computing, Instruction set architecture

reduced instruction set computer

[ri¦düst in′strək·shən ‚set kəm′pyüd·ər]
(computer science)
A computer in which the compiler and hardware are interlocked, and the compiler takes over some of the hardware functions of conventional computers and translates high-level-language programs directly into low-level machine code. Abbreviated RISC.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Reduced Instruction Set Computer

(RISC) A processor whose design is based on the rapid execution of a sequence of simple instructions rather than on the provision of a large variety of complex instructions (as in a Complex Instruction Set Computer).

Features which are generally found in RISC designs are uniform instruction encoding (e.g. the op-code is always in the same bit positions in each instruction which is always one word long), which allows faster decoding; a homogenous register set, allowing any register to be used in any context and simplifying compiler design; and simple addressing modes with more complex modes replaced by sequences of simple arithmetic instructions.

Examples of (more or less) RISC processors are the Berkeley RISC, HP-PA, Clipper, i960, AMD 29000, MIPS R2000 and DEC Alpha. IBM's first RISC computer was the RT/PC (IBM 801), they now produce the RISC-based RISC System/6000 and SP/2 lines.

Despite Apple Computer's bogus claims for their PowerPC-based Macintoshes, the first RISC processor used in a personal computer was the Advanced RISC Machine (ARM) used in the Acorn Archimedes.
This article is provided by FOLDOC - Free Online Dictionary of Computing (
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Under five agreements signed late last fall, the three companies will jointly develop PowerPC microprocessors for use in low-cost RISC (Reduced Instruction Set Computing) systems, an open-systems operating platform, object-oriented software, multimedia technologies and Apple to IBM systems networking.
In the last several years, we have had very interesting switches in who we consider to be our major competitor: we had TI, then Motorola, then DEC, and today maybe it is the Reduced Instruction Set Computing (RISC), generically.
Patterson was cited by the Awards Committee for "his pioneering work on RISC (reduced instruction set computing) which has gained him national and international recognition as a leader in the advancement of computer technology.

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