(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.