[TUHS] Clever code

[Stuff Received]

On 2022-12-13 10:10, Douglas McIlroy 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.

I had always thought of a delay line as a precursor to a register (or 
stack) for storing intermediate results.  Is this not an accurate way of 
thinking about it?

N.


> 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 at skeeve.com> wrote:
>>
>> Douglas McIlroy <douglas.mcilroy at 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