The first computer I ever worked on had 8KB of core memory. It was an old Digital Equipment Corporation pdp-8/e. I loved that machine and its open face tale drives and teletype with paper tape punch and reader and card reader.

  • redcalciumEnglish
    6•1 year ago

    Is that… 32 bytes of memory? Wow, I didn’t know they also came in rope form factor as well.

    Some cores appear to touch other neighboring cores. Won’t that cause issues to the core’s magnetic properties?

      • redcalciumEnglish
        2•1 year ago

        After digging some more, looks like core rope memory is different than the magnetic core memory in your link above (seems to describe magnetic core memory instead of rope memory). Core rope memory is used for ROM while magnetic core memory is used for RAM, and they have different working mechanism.

        Another form of core memory called core rope memory provided read-only storage. In this case, the cores, which had more linear magnetic materials, were simply used as transformers; no information was actually stored magnetically within the individual cores. Each bit of the word had one core. Reading the contents of a given memory address generated a pulse of current in a wire corresponding to that address. Each address wire was threaded either through a core to signify a binary [1], or around the outside of that core, to signify a binary [0]. As expected, the cores were much larger physically than those of read-write core memory. This type of memory was exceptionally reliable. An example was the Apollo Guidance Computer used for the NASA Moon landings.

        Basically, 1 if the sense wire going through the core, or 0 if the wire bypass the core. You basically woven 1 and 0 manually into the rope. And yeah, it doesn’t matter if the cores touch each other as long as the wires are woven correctly. This article have some wiring diagram for the core rope memory: http://www.righto.com/2019/07/software-woven-into-wire-core-rope-and.html .

        • @sixfoldEnglish
          2•1 year ago

          Oh, my bad, I linked the wrong page!, edited to include both

          • redcalciumEnglish
            2•1 year ago

            All this stuff is really cool! Looks like you can use one ring to store multiple bits by using multiple sense wire. So that’s why there are a lot of wires in the images. Seems like there are 16 bits for each core?

            I wonder how feasible it is for someone to built their own retro computers by soldering a bunch of nand gates and weaving their own ram and rom. The only problem seems to be getting the ferrite cores in huge quantities (are those still being sold these days?).

            • @sixfoldEnglish
              3•1 year ago

              I totally want to try, I think ferrite toroids are everywhere, but the material that core/rope memory rings are made of has a specific magnetic response hysteresis which is important.

              • redcalciumEnglish
                2•1 year ago

                There goes my dream building my own computer if I survived a nuclear apocalypse.

    • @sixfoldEnglish
      4•1 year ago

      Oh, I see what you mean by

      Is that… 32 bytes of memory?

      No, each wire that goes through the rope, weaving through or around each of the ferrite rings, represents one or multiple bytes.

      • redcalciumEnglish
        2•1 year ago

        Looks like there are 16 wires for each core in this module?