TLDR: each CPU instruction takes the exact amount of time it does on the real cpu. You generally only care about cycles in real-time stuff. In simpler CPUs lik

TLDR: each CPU instruction takes the exact amount of time it does on the real cpu. You generally only care about cycles in real-time stuff. In simpler CPUs like those used for microwaves and such, each CPU instruction takes constant time. You can count the number of instructions in your assembler loop and know how long the loop will take. Mind you sometimes each instruction takes constant time but some can take more time than others. A cpu cycle is defined as 1/clockspeed . A fast instruction can take 1 cycle, others 3 or more. Usually there's multiple cpu instructions for GOTO and loading from memory, a fast set for things "close by" and a slow set for far away code or data. Loops and conditional instructions even on simple cpus can take different amounts of time depending on the outcome, so it gets pretty complicated to time things sometimes. So when doing really low level timing critical code, you can use a super accurate signal generator to drive your CPU clock, then count your instructions to time things. Common uses include generating audio from bit banging and similar. In more complex CPUs a number of things made it difficult or impossible to figure out exactly how long an instruction will take. None of the software for these CPUs is written to depend on exact cycle timings. Because nothing depends on cycle accuracy you don't have to worry about the timings when emulating these kinds of CPU's.