[TUHS] Re: Clever code

[Marc Donner <marc.donner@gmail.com>]

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Here is a page from the Computer History Museum on the topic:
https://www.computerhistory.org/revolution/memory-storage/8/309

about halfway down the page is a nice schematic.
=====
nygeek.net
mindthegapdialogs.com/home <https://www.mindthegapdialogs.com/home>


On Thu, Dec 15, 2022 at 1:06 PM Marc Donner <marc.donner@gmail.com> wrote:

> Further on delay line storage:
>
> Physically one of the most common ones was a cylinder of liquid mercury.
> There was a device at one end for introducing pressure waves into the
> mercury (think loudspeaker) and a device at the other end for measuring the
> pressure waves arriving (think microphone).  The pulses that came off the
> microphone end were then fed back to the loudspeaker end, after being
> cleaned up.
> =====
> nygeek.net
> mindthegapdialogs.com/home <https://www.mindthegapdialogs.com/home>
>
>
> On Tue, Dec 13, 2022 at 10:12 AM 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
>>
>

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