No matter how memory technology marches on, magnetic core memory is still cool. Radiation-hard, nonvolatile, and so pretty. What’s there not to love? [Mark Nesselhaus] is no stranger to fun in-your-face electronics builds — judging from his hackaday.io projects — and this entry to the Hackaday Op-Amp contest is no outlier. This is a sixteen-bit magnetic core RAM demonstrator built upon glass using copper tape and solder, which always looks great and is actually not all that hard to do yourself provided you grab a new scalpel blade from the pack before starting.
For the uninitiated, the crossed X and Y wires each host a hard magnetic toroid which can only be magnetised by a field beyond a certain threshold due to the shape of the B-H curve of ferrite materials. The idea is for a required threshold current, drive the selected X line and Y line each with a current half of this value, so that only the selected core bit ‘sees’ the full field value, and flips state. This means that only a single bit can be written for each core plane, so to form longer words these layers are stacked, producing some wonderful cubic structures. These magnetic circuits are responsible for putting a human on the moon.
Reading the bit state is basically the opposite. A third sense wire is passed sequentially through each bit in the array. By driving a current the opposite way through the selected core bit, if the core was previously magnetised then the sense wire will read a short pulse that can be amplified and registered. The eagle-eyed will realise that reading is a destructive process, so this needs to be followed up by a write-back process to refresh the bit, although the core state will persist without power, giving the memory nonvolatile behaviour.
[Mark] utilises a simple discrete transistor differential transformed-coupled front end which senses the tiny current pulse and passes it along to a Set-Reset latch for visualisation. This simple concept could easily be extended to make this a practical memory, but for now, addressing is courtesy of a pair of crocodile clips and a discrete write/read pulse switch. We will watch with interest how far this goes.
DIY core memory builds are not a regular occurrence around these parts, but we see them from time to time, like this polished 64-bit setup. Core arrays are not the only magnetic memory in town, we’ve also seen DIY core rope memories as well.
What do you do when you’ve bought some old Soviet core memory modules on eBay? If you are [CuriousMarc], you wire it up to some test connectors and use your test bench to see if the core memory still works. Spoiler alert: it does.
While it seems crude by today’s standard, there was a time when these memory modules would have been the amazing miniature tech of their day. Each little magnetic torus represents a bit and the modules have 1,024 and 4,096 tiny little donuts strung together in a grid.
We don’t know why [TubeTime] decided to show off this oddball keyboard switch as a series of Twitter posts, but we were glad to see them somewhere. At first, the switch looks pretty conventional. But as the pictures reveal the insides, you’ll notice something unusual: a ferrite toroid! These switches operate as a transformer and are known as magnetic valve switches.
The switches have two sets of two pins — one set for the primary and one for the secondary of the transformer wound around the ferrite core. That transformer remains stationary, but a pair of permanent magnets move. When the key is up, the magnets are close to the core and cause the transformer to saturate, so there is little or no output at the secondary. When you depress the key, the magnet moves away from the core, allowing the signal to pass through the transformer. What that means is there is no mechanical contact, which is good for switch life. It is also important in environments where a small spark could cause an explosion. You can watch a video about a keyboard that used those switches, below.
As the dashing officer shown above will tell you, early data processing machines and ADP systems employed two types of magnetic cores for memory and other purposes. This 1961 U.S. Army training film is an introduction to the properties of ferrite cores, which are commonly made from nickel alloy and other magnetic materials. As this is only part one of a series, the metallic ribbon type of magnetic core is covered in some other segment we have yet to locate.
The use of magnetic cores for random access memory was built upon transformer theory and provided a rugged and low-power solution until the semiconductor came into vogue. Before that time, the humble ferrite core served many uses and did so very well. The Apollo Guidance Computer had erasable magnetic core memory, and much of its software was stored in core rope memory.
The film covers a lot of theory and does so clearly and concisely. It begins by explaining what a magnetic core is and why it’s used, and then moves on to describe how the cores are used to store bits and the method by which they can transfer information to other cores. Along the way, it provides background on bi-stable devices and provides explanation of magnetization behavior in terms of magnetizing force and flux density.
We’ve seen NAND and NOR logic gates – the building blocks of everything digital – made out of everything from marbles to Minecraft redstone. [kos] has outdone himself this time with a logic circuit we’ve never seen before. It’s based on magnets and induction, making a NOR gate out of nothing but a ferrite core, some wire, and a diode.
The theory of operations for this magnetic NOR gate goes as follows: If two of the input windings around the core have current passing in different directions, the fields cancel out. This could either be done by positive or negative voltages, or by simply changing the phase of the winding. To keep things simple, [kos] chose the latter. The truth table for a simple two-input, one-output gate gets pretty complicated (or exceedingly cool if you’d like to build a trinary computer), so to get absolute values of 1 and 0, a separate ‘clock’ winding was also added to the core.
One thing to note about [kos]’ gate is its innovation on techniques described in the relevant literature. Previously, these kinds of magnetic gates were built with square ferrites, while this version can work with any magnetic core.
While this isn’t a very practical approach towards building anything more complex than a memory cell, it is an exercise of what could have been in an alternate universe where tube technology and the transistor just didn’t happen.
Magnetic core memory was used from the 1950s through the 1970s, and provided a non-volatile means for storing data, as each magnetic core retained its orientation, even when the power was cut. While it sounds a lot like a modern hard drive, these devices were used in the same fashion as RAM is utilized today.
While the pair used surplus ferrite cores manufactured just before magnetic memory stopped being produced, they did allow themselves to use some modern components. Items such as transistors and logic gates were not available to the first magnetic core memory manufacturers, but the use of these items helped them complete the project in a reasonable amount of time.
Their final result is a magnetic memory board which can be used by any USB-enabled device and is reliable enough to withstand billions of read/write transactions.