Planet Arduino

About ten years ago, we designed and made an Arduino shield implementing “core memory,” a technology that was sixty years old even then. Our shield stored 32 individual 1s or 0s using magnetic fields going either clockwise or anticlockwise around 32 tiny doughnuts of magnetisable ‘ferrite’ material. This kind of memory, invented in the 1950s, […]

The post Core Memory: Why We Used 60-Year-Old Tech in an Arduino Shield appeared first on Make: DIY Projects and Ideas for Makers.

[Andy Geppert] sends in his incredibly clever interactive core memory shield. 

In a great display of one hacker’s work being the base for another’s, [Andy] started out with [Jussi Kilpelainen]’s core memory shield for Arduino.  As he was playing with the shield he had a desire to “see” the core memory flipping and got the idea to add an LED matrix aligned behind the individual cores.

The first iteration worked, but it only showed the state that the Arduino believed the core memory to be in. What he really wanted was a live read on the actual state. He realized that an Adafruit Featherwing 8×8 matrix display also fits behind the core memory. Now the LEDs update based on the read state of the core memory. This allows him to flip the individual bits with a magnetic stylus and see the result. Very cool.

You can see a video of it working after the break.

If you’ve heard of core rope memory, it will probably be in the context of vintage computing equipment such as Apollo-era NASA hardware. A string of magnetic cores and sense wires form a simple ROM arrangement, which though long-ago-superceded by semiconductor memory remains possible to recreate by the experimenter. It’s a path [Nicola Cimmino] has trodden, as he’s not only made a few nibbles of core rope memory, but incorporated it with an Arduino as part of one of the most unusual LED flashers we’ve ever seen. The memory holds a known sequence of bits which is retrieved in sequence by the Arduino, and the LED is kept flashing as long as the read values conform to those expected.

The memory itself is simple enough (and not to be confused with magnetic core memory). The cores are ferrite rings that form a sequence of small transformers that become the bits of the memory. Individual bits are set high or low by either passing a sense wire through a core to create a primary, or bypassing it. Multiple sense wires can be used for separate nibbles in the same cores, so for example his four nibbles all share the same four cores. Pulses are sent down the wires, either passing through a core or not, and equivalently picked up or not on sense lines.

In this case the sense wire is driven directly to ground by Arduino pins which means that the circuit is relying upon the current limiting of the ATmega328 to avoid destroying itself, it’s possible we’d add a driver transistor. The bits are read meanwhile from the secondary windings through a diode rectifier and capacitor to an Arduino analogue pin.

Core memory has been paired with an Arduino before on these pages, though of the RAM variety.

Linux programs, when they misbehave, produce core dumps. The reason they have that name is that magnetic core memory was the primary storage for computers back in the old days and many of us still refer to a computer’s main memory as “core.” If you ever wanted to have a computer with real core memory you can get a board that plugs into an Arduino and provides it with a 32-bit core storage. Of course, the Arduino can’t directly run programs out of the memory and as designer [Jussi Kilpeläinen] mentions, it is “hilariously impractical.” The board has been around a little while, but a recent video shined a spotlight on this retro design.

Impractical or not, there’s something charming about having real magnetic core memory on a modern CPU. The core plane isn’t as dense as the old commercial offerings that could fit 32 kilobits (not bytes) into only a cubic foot. We’ll leave the math about how much your 8-gigabyte laptop would have to grow to use core memory to you.

Honestly, this is purely a novelty, but we do miss core memory somewhat. It was inherently nonvolatile. You could turn the computer off, turn it back on, and everything was just how you left it. Sure, it was peculiar that reading a bit also destroyed it, but many of the old computers had the write after read cycle built into the CPU architecture so that it wasn’t a big deal.

If you want to look at how it was to repair a big core system, we looked at that earlier. Surprisingly, though, this isn’t the first Arduino core memory rig we’ve seen.