"the apple ][ had HW with dependencies on the CPU being at a certain rate" On the other hand something like a KIM-1 would be totally doable although there woul

"the apple ][ had HW with dependencies on the CPU being at a certain rate" On the other hand something like a KIM-1 would be totally doable although there would have to be changes to the cassette interface and TTY interface software timing loops. Oh and I suppose if you clocked below 10 KHz or something then keypad debounce routines might need some work. But from memory there would be no hardware changes necessary to downclock a KIM-1. There is a hardware PLL in the cassette interface input but all it does is sniff if the incoming tone is above or below some frequency A KIM-1 was a rather simple 6502 single board computer from the dawn of the microcomputer era.