Reduced Instruction Set Computer
<processor> (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.
(1997-06-03)
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