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 On Thu, Dec 15, 2022 at 1:06 PM Marc Donner 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 > > > 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 wrote: >> > >> > Douglas McIlroy 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 >> >