VCF East 2023: Andy Geppert Talks Core Memory

Do you know core memory? Our prehistoric predecessors would store data in the magnetic fields of ferrite rings, reading out the ones and zeroes by setting the magnetic field and detecting if a small current is induced in a sense wire, indicating that the bit flipped, or not detecting the current, in which case it didn’t. Core memory is non-volatile, rad hard, and involved a tremendous amount of wire weaving to fabricate. And it’s pretty cool.

[Andy Geppert] wants to get you hands-on with this anachronistic memory, and builds kits to demo how it works. [Tom Nardi] and [Bil Herd] caught up with him at the Vintage Computer Festival East last weekend, and got him to demo his Core64 project for them. (Video, embedded below.)

The design of Core64 displays its state in lights at all times. And this means that you can write to it using either the onboard Pi Pico, for a blinky light show, or with a magnetic stylus, setting each bit’s magnetic state by hand. This turns it into a magnetic memory tablet and is a sweet demonstration of the principles that make it all work. Or, if you pulse the lines at just the right frequency, you can make the cores spin!

Watch [Andy] explaining it in our interview here, and stay tuned for more coming from VCF East 2023 soon.

18 thoughts on “VCF East 2023: Andy Geppert Talks Core Memory

    1. What is the .000 represent? A 1/1000 of a core? :) Those would tough to weave ;) ha!

      I too, at this stage of life, not to interested in ‘weaving’ the cores for fun. I do remember, when I was working at my first job, an HP computer they were phasing out had core memory. Loaded the computer with paper tape I believe. One of our engineers still has one of those folding cards of core memory for fun.

      1. If you speak Python that would be 100_000
        or if you´re a bit versed into science, it would be 1E5
        or 100k cores.

        if you still don´t get it then you should travel a bit. USe your feet to drag your pounds across the yard.

      2. In FORTH you write double length integers as digits with punctuation inside, I used “_” and “.” years ago. So “100.000” would be how to write 100,000 into a 16 bit FORTH as a 32 bit double integer.

    1. Oops – meant to post this in response to [Andrew Starr]’s project, not [Chris]’ comment above. Oops. Alas, if people have spare core memory definitely send it to someone who can put it to use (me included!) because I think it will become extremely hard to come by N.O.S. in the future. Here’s what I meant to say to [Andrew Starr]:
      “Your project was an inspiration to me! I have provisioned my design to be able to stack 8 planes, but I haven’t actually done it yet. I have in mind that I’ll add a stack of 8 planes to my demo in the near future, and then use a small LCD screen to render a real-time isometric view of the state of each core in the stack. Hoping to make it a 3 dimensional flux detector!”

  1. While core memory is usually thought of as mainframe or high tech use it did find it’s way into the more mundane applications. NCR (National Cash Register) used it in a cash register/terminal known as the NCR 280. The 4k core held a program that handled basic offline sales with tax calculations storage and online communication data flow via DLC (12v async) to a central multiplexor (NCR 751) which in turn provided synchronous communication to a mainframe for the SKU pricing and inventory control. Multiple terminals in multiple stores were handled via Poll/Select protocols. Printing format of the customer receipt was also in the program and outputted to a Helical Printer. The NCR 280 could be found in the likes of Bergners, Pennys, Sears, Wards and other large chain retailers. In the Midwest, winter was my most favorite time. I would be at Bergners cleaning a printer and would cringe at the snap of static when a salesperson walking across the carpet would touch a 280. The core would take an immediate dump. That meant I would be spending about an hour keying in the main program because there were no download capabilities at that time.

  2. Thank you to the Hackaday team members who made this post possible. Very nice of you! I draw a lot of inspiration from this community and I’m honored to have been highlighted with my obscure little project!

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