Magnetic Core memory was the RAM at the heart of many computer systems through the 1970s, and is undergoing something of a resurgence today since it is easiest form of memory for an enterprising hacker to DIY. [Han] has an excellent writeup that goes deep in the best-practices of how to wire up core memory, that pairs with his 512-bit MagneticCoreMemoryController on GitHub.
Magnetic core memory works by storing data inside the magnetic flux of a ferrite ‘core’. Magnetize it in one direction, you have a 1; the other is a 0. Sensing is current-based, and erases the existing value, requiring a read-rewrite circuit. You want the gory details? Check out [Han]’s writeup; he explains it better than we can, complete with how to wire the ferrites and oscilloscope traces to explain why you want to wiring them that way. It may be the most complete design brief to be written about magnetic core memory to be written this decade.
This little memory pack [Han] built with this information is rock-solid: it ran for 24 hours straight, undergoing multiple continuous memory tests — a total of several gigabytes of information, with zero errors. That was always the strength of ferrite memory, though, along with the fact you can lose power and keep your data. In in the retrocomputer world, 512 bits doesn’t seem like much, but it’s enough to play with. We’ve even featured smaller magnetic core modules, like the Core 64. (No prize if you guess how many bits that is.) One could be excused for considering them toys; in the old days, you’d have had cabinets full of these sorts of hand-wound memory cards.
Magnetic core memory should not be confused with core-rope memory, which was a ROM solution of similar vintage. The legendary Apollo Guidance Computer used both.
We’d love to see a hack that makes real use of these pre-modern memory modality– if you know of one, send in a tip.
[Curious Marc] has an excellent YouTube video detailing the waveform requirements.
https://youtu.be/AwsInQLmjXc
I think Ferromagnetic RAM (Ramtron ??) is a scaled down (physical size) of magnetic core store memory. Low power, read/write into billions of cycles and much faster than EEPROM.
Where can one get these “special” magnetizable ferrite cores? They aren’t yer normal Digikey or Mouser (or Amidon or Micrometal) part intended for RF transformers or EMI chokes.
Are the existing stocks all NOS?
Are they still even being manufactured? If so, what for?
There’s a link in the original article to an Bulgarian ebay-seller of ferrite cores, manufactured in Hermsdorf, GDR….
You can still get them NOS on everybody’s favourite untrustworthy online auction site. They are sold by the thousands in little tins for very little money.
Core memory is always very exciting, even if it’s not very practical (Transistor/Capacitor arrays can create DIY DRAM and Diodes can be used for Diode Matrix ROMs). But it is exciting. In the write up says:
“1.3mm Diameter Special Ferrite Core (regular ferrite will not work)”
Where do you get those from?
In the 1960s I understand that thousands of poorly paid women in East Asia were employed to make core memory as it couldn’t be fully automated.
LOL. It wasn’t just in East Asia. When I was a teenager Control Data in Minneapolis was paying housewives and kids to wire up core memory in their garages. I suspect that they were poorly paid as well.
Wonder how dense ferrite memory could be as a mems ic
Basically like flash, but don’t hold a magnet nearby
not MEMS, but for chip-scale magnetic memory there exists (at least) FeRAM, thin-film memory, and bubble memory.
Magnetorestrictive memory is probably where it’s at– 1GB fits on a postage stamp. Which simultaniously amazing compared to ferrite core and pathetic compared to flash.
magnetostrictive you mean?
Not non-volatile like the rest of these mentioned here.
Isn’t magnetostrictive memory serial access, e.g., you have to wait for the bits to circulate to the receive transducer before you can use them? Albeit, on a tiny scale with lots of relatively small loops and higher data rates, that delay might not matter, but it is still there. The controller might hide some of it, but inherently, it is still a bit-serial technology. Not to mention, it loses all content when the power is turned off. Many old electronic calculators from the mid-1960’s through the early 1970’s used magnetostrictive delay lines as their main memory element. While not fast, it was a heck of a lot faster than a motor-driven mechanical calculator. Eventually MOS shift registers replaced the delay lines, but they MOS wasn’t nearly as “cool” as a coils of special wire with a bunch (well, for the time…maybe like 1200 or so) of bits packed into it as torque pulses.
512 bits of RAM may not seem like much, but that’s how much RAM an ATtiny13 microcontroller has and I’ve built plenty of useful things with them. The 1KB of flash is a much larger limitation than the 64B of RAM.