That doesn’t seem right to me. Of course a context switch includes the memory protection, but in a traditional OS there are also registers and other CPU state

That doesn’t seem right to me. Of course a context switch includes the memory protection, but in a traditional OS there are also registers and other CPU state that need to be saved since a process can be interrupted just about anywhere. I suppose that I’m idealising a bit here but ISTM that the structure of FOMOS means that the CPU state doesn’t need to be saved, so the context switch involves only memory protection, register resets, stack pointer reset and little else. You don’t even need to preserve the stack between invocations. And unlike preemptive multitasking, there seems to be little or no writing to memory needed, which would seem to obviate a bunch of contention. (Noting that it’s 30 years since I fiddled with operating systems at this level) Frankly I find this really elegant and exciting.