Instruction set architecture: Difference between revisions

Revision as of 15:41, 10 August 2025

Revision as of 15:44, 10 August 2025

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{{Machine code}}

An '''instruction set architecture''' (ISA) is an [[abstract model]] that defines the programmable [[interface (computing)|interface]] of the [[CPU]] of a computer; how [[software]] can control a computer.<ref>{{Cite web |title=GLOSSARY: Instruction Set Architecture (ISA) |url=https://www.arm.com/glossary/isa |archive-url=https://web.archive.org/web/20231111175250/https://www.arm.com/glossary/isa |archive-date=2023-11-11 |access-date=2024-02-03 |website=arm.com}}</ref> A device (i.e. CPU) that interprets instructions described by an ISA is an [[implementation]] of that ISA. Generally, the same ISA is used for a family of related CPU devices.

In general, an ISA defines the supported [[Machine code|instructions]], [[data type]]s, [[Register (computer)|registers]], the hardware support for managing [[Computer memory|main memory]],{{Clarify|date=April 2024|reason=See "What does "Hardware support for managing main memory" refer to?" on the talk page.]]}} fundamental features (such as the [[memory consistency]], [[addressing mode]]s, [[virtual memory]]), and the [[input/output]] model of implementationsthe of theprogrammable ISAinterface.

An ISA specifies the behavior ofimplied by [[machine code]] running on implementationsan implementation of that ISA in a fashion that does not depend on the characteristics of that implementation, providing [[binary compatibility]] between implementations. This enables multiple implementations of an ISA that differ in characteristics such as [[Computer performance|performance]], physical size, and monetary cost (among other things), but that are capable of running the same machine code, so that a lower-performance, lower-cost machine can be replaced with a higher-cost, higher-performance machine without having to replace software. It also enables the evolution of the [[microarchitecture]]s of the implementations of that ISA, so that a newer, higher-performance implementation of an ISA can run software that runs on previous generations of implementations.

If an [[operating system]] maintains a standard and compatible [[application binary interface]] (ABI) for a particular ISA, machine code will run on future implementations of that ISA and operating system. However, if an ISA supports running multiple operating systems, it does not guarantee that machine code for one operating system will run on another operating system, unless the first operating system supports running machine code built for the other operating system.