Overview
The ISA is the interface between the hardware and the software. It defines the instructions (like add, subtract, load, store) that the CPU understands, as well as the registers and memory model.
Major ISAs
- x86 / x86-64: Dominant in desktops and servers (Intel, AMD).
- ARM: Dominant in mobile devices and increasingly in laptops (Apple, Qualcomm).
- RISC-V: An open-standard ISA gaining popularity in embedded systems and research.
Importance
Software must be compiled for a specific ISA to run on a processor. This is why you cannot run Windows for x86 directly on an ARM-based smartphone without emulation.