For extra speed, a lot of emulators take shortcuts. So, you might have a "frame-accurate" emulator that doesn't match the state of a "real" Nintendo on a cycle-

For extra speed, a lot of emulators take shortcuts. So, you might have a "frame-accurate" emulator that doesn't match the state of a "real" Nintendo on a cycle-by-cycle basis, but does by the end of the frame. There are a limited number of things triggered in the hardware (interrupts, set register flags, etc), and sometimes, like when the CPU is in an idle loop, the emulator can just skip ahead by a bunch of instructions until the next thing that needs to be handled. Or in the graphics processor, maybe you'll blit out whole sprites/tiles at once, instead of rendering them pixel-by-pixel, the way that the hardware does. In a cycle-accurate emulator, you're going to run every opcode, process the graphics pixel-by-pixel, etc.