The Power architecture is a family of RISC instruction sets with roots in IBM’s POWER (Performance Optimization With Enhanced RISC) processors of the early 1990s. In 1991 IBM, Apple, and Motorola formed the AIM alliance and adapted POWER into PowerPC, a single-chip RISC architecture intended for desktops and embedded systems. PowerPC went on to power Apple’s Macintosh line for more than a decade, as well as game consoles and a wide range of embedded controllers.
Over time IBM’s server-oriented POWER line and the AIM PowerPC line were reconciled into a single unified specification, the Power ISA. That specification is the architecture’s primary, authoritative document. The OpenPOWER Foundation’s Instruction Set Architecture page explains that the Power ISA “describes the architecture used by POWER processors and defines the instructions the processor executes,” organized into a User Instruction Set Architecture for application programmers, a Virtual Environment Architecture for the storage model, and an Operating Environment Architecture for supervisor-level facilities.
As a RISC design, the Power ISA emphasizes a load-store model in which arithmetic operates only on registers, a large register file, and instructions that decode cleanly for pipelined and superscalar execution. These traits let Power implementations scale from low-power embedded parts up to IBM’s high-end POWER server processors, all conforming to the same published instruction-set contract.
The most significant recent change is openness. IBM placed the Power ISA under a royalty-free license and handed stewardship to the OpenPOWER Foundation, which now maintains the specification and an RFC process through which members propose changes. This made Power one of the major instruction-set architectures available for anyone to implement without licensing fees, alongside RISC-V, rather than remaining a single-vendor design.
The Power ISA’s arc, from a proprietary IBM server architecture, through a cross-company desktop alliance, to an openly governed standard, mirrors a broader industry shift. It shows how an instruction set that began as one company’s competitive advantage could be turned into shared, openly specified infrastructure.