What are instruction set architectures?

Question

I know some examples are x96, x64 and arm. Are they abstract models of computation, like Turing machines?

In: 2

Answer 1

Sort of. They describe how a specific archetype of cpu handles registers, instructions, data types, memory addressing and so on. It tells you two different CPUs will run machine code in exactly the same way with exactly the same outcome even if they differ greatly in how they physically do it.

Grossly oversimplified: it doesn’t matter if cpu A calculates 4+(5+6) and cpu B calculates (4+5)+6 because we know they both use decimal architecture and return 15. Cpu C uses octal architecture and would have returned 17.