Acronym for Reduced Instruction Set Computer. A CPU 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 that are generally found in RISC designs are uniform instruction encoding, in which the operating code always occupies the same bit positions in each instruction, which is always one word long. This allows faster decoding. RISC also provides for a homogenous register set, allowing any register to be used in any context and simplifying compiler design. Simple addressing modes replace complex modes with sequences of simple arithmetic instructions.
RISC processing was developed by IBM in the early 1970s. The most common examples of computers with RISC-based CPUs are the Apple Power Mac series. And if you can stand to learn one more acronym, the “Power” in that name is IBM’s acronym for “Performance Optimization With Enhanced RISC.”