Reduced Instruction Set Computer

Why Trust Techopedia

What Does Reduced Instruction Set Computer Mean?

A reduced instruction set computer (RISC) is a computer that uses a central processing unit (CPU) that implements the processor design principle of simplified instructions. To date, RISC is the most efficient CPU architecture technology.

Advertisements

This architecture is an evolution and alternative to complex instruction set computing (CISC). With RISC, the basic concept is to have simple instructions that do less but execute very quickly to provide better performance.

Techopedia Explains Reduced Instruction Set Computer

The most basic RISC feature is a processor with a small core logic that allows engineers to increase the register set and increase internal parallelism by using the following:

  • Thread level parallelism: Increases the number of parallel threads executed by the CPU
  • Instruction level parallelism: Increases the speed of the CPU's executing instructions

The words "reduced instruction set" are often misinterpreted to refer to a reduced number of instructions. However, this is not the case, as several RISC processors, like the PowerPC, have numerous instructions. At the opposite end of the spectrum, the DEC PDP-8, a CISC CPU, has only eight basic instructions. Reduced instruction actually means that the amount of work done by each instruction is reduced in terms of number of cycles – at most only a single data memory cycle – compared to CISC CPUs, in which dozens of cycles are required prior to completing the entire instruction. This results in faster processing.

Advertisements

Related Terms

Margaret Rouse
Senior Editor
Margaret Rouse
Senior Editor

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.