AFAIR it was quite efficient (basically free) on pre-VM PDP-11 where the kernel swapped the whole address space on a context switch. It only involved swapping to a new disk area.
AFAIR it was quite efficient (basically free) on pre-VM PDP-11 where the kernel swapped the whole address space on a context switch. It only involved swapping to a new disk area.
I used MINIX on 8086 which was similar and it definitely was not efficient. It had to make a copy of the whole address space on fork. It was the introduction of paging and copy-on-write that made fork efficient.
Oh, is that how MINIX did that? AIUI, the original UNIX could only hold one process in memory at a time, so its fork() would dump the process's current working space to disk, then rename it with a new PID, and return to the user space — essentially, the parent process literally turned into the child process. That's also where the misconception "after fork(), the child gets to run before the parent" comes from.