[TUHS] Re: Clever code

[arnold@skeeve.com]

Thank you for the explanation.  The skill of the programmers who had to
write code for such machines amazes me. I might could have held all
that kind of info in my head when I was younger, but certainly not today...

Thanks,

Arnold

Douglas McIlroy <douglas.mcilroy@dartmouth.edu> wrote:

> A delay line is logically like a drum, with circulating data that is
> accessible only at one point on the circle. A delay line was
> effectively a linear channel along which a train of data pulses was
> sent. Pulses received at the far end were reshaped electronically. and
> reinjected at the sending end. One kind of delay line was a mercury
> column that carried acoustic pulses.. The PB 250 delay line was
> magnetostrictive (a technology I know nothing about).
>
> If instruction timing is known, then the next instruction to appear is
> predictable. The only caveat is that instruction times should not be
> data-dependent. You can lay out sequential code along the circle as
> long as no instruction steps on one already placed. When that happens
> you must switch modes to jump to an open spot, or perhaps insert nops
> to jiggle the layout.
>
> Doug
>
> On Tue, Dec 13, 2022 at 9:31 AM <arnold@skeeve.com> wrote:
> >
> > Douglas McIlroy <douglas.mcilroy@dartmouth.edu> wrote:
> >
> > > Apropos of accessing rotating storage, John Kelly used to describe the
> > > Packard-Bell 250, which had a delay-line memory, as a machine where
> > > addresses refer to time rather than space.
> > >
> > > The PB 250 had two instruction-sequencing modes. In one mode, each
> > > instruction included the address of its successor. In the other mode,
> > > whatever popped out the delay line when the current instruction
> > > completed would be executed next.
> > >
> > > Doug
> >
> > For us (relative) youngsters, can you explain some more how delay
> > line memory worked? The second mode you describe sounds like it
> > would be impossible to use if you wanted repeatable, reproducible
> > runs of your program.
> >
> > Thanks,
> >
> > Arnold