cmurillo(a)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 --
www.jetnet.ab.ca/users/bfranchuk/index.html