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 registerset, 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 BerkeleyRISC, 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 RISCSystem/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)