Glossary comparison
ISA vs Microarchitecture: what is the difference?
The difference
The ISA says what the processor does as seen by software. The microarchitecture is how one design does it internally; two microarchitectures of the same ISA can differ greatly in speed and power.
The ISA is the contract software relies on. The microarchitecture is one way of implementing it, and can change between generations without breaking software.
The two terms
ISA
The contract between hardware and software: the instructions, registers, memory model and exception behaviour a processor exposes. Binary compatibility and the surrounding software ecosystem follow the ISA, not the microarchitecture.
Microarchitecture
The internal organisation of a processor that implements an ISA, covering pipeline depth, issue width, caches, branch predictors and execution units. Two microarchitectures can run identical binaries at very different speeds.
Side by side
| Field | ISA | Microarchitecture |
|---|---|---|
| Stands for | Instruction Set Architecture | Not an abbreviation |
| Type | Acronym | Term |
| Domain | Compute & AI Hardware | Design & Architecture |
| Group | CPU architecture | Processor architecture |