Yep, exactly. For instance the natural calling convention on the PDP-8 was that the return address was stored before the contents of the called function (i.e.

Yep, exactly. For instance the natural calling convention on the PDP-8 was that the return address was stored before the contents of the called function (i.e. in C terms it looked like "funcaddr[-1] = pc; pc = funcaddr;") I think other machines of that vintage and older were similar. This meant you could support function calling without the need for a stack. However you can't directly support recursive (or co-recursive) functions. Nor could you ever do things like multithreading or shared libraries, although hose obviously weren't concerns at that time. Today we think of the callstack as a fundamental part of the machine architecture, but at the time of algol-60 it was still a very contentious subject.