I think the IBM S/360 was 'stack challenged' too, iirc //Rich Hi, I found this really interesting: The PDP-8 has no concept of a stack. It does have sub-routines though. Instead of pushing the instruction pointer onto a stack, it's being written at the location to which the call is directed (first address of the subroutine). Then a return is simply an indirect jump to that first address of the subroutine. This is hillarious! Wasn't the notion of a stack arond already before 1965? fun stuff, isn't it?