if you hadn't already known this about the PDP-8

From: Ben Franchuk <bfranchuk_at_jetnet.ab.ca>
Date: Wed Dec 12 18:45:12 2001

cmurillo_at_multi.net.co wrote:
> Gunther wrote:
> >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?
> Interesting... I suppose that it had to do with the fact
> that the pdp8 was supposed to be affordable...
I can think of two other good reasons that a stack was not
found on a PDP-8. First is was based on the PDP-5 a digital
controller , not a general computer. Second there is no room
for stack instructions in the order code with only a 12 bit
word width. Having a hardware JSR has a real feature of
the instruction set.

A a side note stack based programs are harder to recover from
when a stack blows up.

BTW If you really need a 12/24 bit processor with stacks,
I have a nice design. A nice cpu but only 1 in existence
still :)
Ben Franchuk --- Pre-historic Cpu's --
Received on Wed Dec 12 2001 - 18:45:12 GMT

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