RISC-reduced instruction set computer

RISC

In the mid-1980s to early-1990s, a crop of new high-performance RISC (reduced instruction set computer) microprocessors appeared, influenced by discrete RISC-like CPU designs such as the IBM 801 and others. RISC microprocessors were initially used in special purpose machines and Unix workstations, but then gained wide acceptance in other roles.

The first commercial microprocessor design was released by MIPS Technologies, the 32-bit R2000 (the R1000 was not released). The R3000 made the design truly practical, and the R4000 introduced the world's first 64-bit design. Competing projects would result in the IBM POWER and Sun SPARC systems, respectively. Soon every major vendor was releasing a RISC design, including the AT&T CRISP, AMD 29000, Intel i860 and Intel i960, Motorola 88000, DEC Alpha and the HP-PA.

Market forces have "weeded out" many of these designs, with almost no desktop or laptop RISC processors and with the SPARC being used in Sun designs only. MIPS is primarily used in embedded systems, notably in Cisco routers. The rest of the original crop of designs have disappeared. Other companies have attacked niches in the market, notably ARM, originally intended for home computer use but since focussed on the embedded processor market. Today RISC designs based on the MIPS, ARM or PowerPC is used in the majority of embedded 32-bit devices, although not in the large quantities in which embedded 8-bit devices are produced (whether CISC or RISC).

As of 2007, two 64-bit RISC architectures are still produced in volume for non-embedded applications: SPARC and Power Architecture. The RISC-like Itanium is produced in smaller quantities. The vast majority of 64-bit microprocessors are now x86-64 CISC designs from AMD and Intel.