All you need for preemptive multithreading is IRQ#0 to generate an interrupt. That's the entirety of it. Preemptive multiprocessing then needs paging and such

All you need for preemptive multithreading is IRQ#0 to generate an interrupt. That's the entirety of it. Preemptive multiprocessing then needs paging and such to make isolated memory a thing as well, but still doesn't need HW context switching.