- Snippet from Wikipedia: Instruction set architecture
An instruction set architecture (ISA) is an abstract model that defines the programmable interface of the CPU of a computer; how software can control a computer. 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 instructions, data types, registers, the hardware support for managing main memory, fundamental features (such as the memory consistency, addressing modes, virtual memory), and the input/output model of the programmable interface.
An ISA specifies the behavior implied by machine code running on an 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 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 microarchitectures 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.
An ISA can be extended by adding instructions or other capabilities, or adding support for larger addresses and data values; an implementation of the extended ISA will still be able to execute machine code for versions of the ISA without those extensions. Machine code using those extensions will only run on implementations that support those extensions.
The binary compatibility that they provide makes ISAs one of the most fundamental abstractions in computing.
instruction_set_architecture
instruction_set_architecture.txt · Last modified: 2025/02/01 06:50 by 127.0.0.1