24k #7 -- Loopy Town

I had wanted to feature the Casio Loopy for our 7th installment of 24k for 24. Alas, I was misinformed. The Casio Loopy video game system actually has a megabyte of RAM, not the 24k that I had somewhere read. I wanted to write about the Loopy because it is one of the very few video game systems that includes a built-in thermal printer (so few that I can't think of another), but mostly because its small library of games includes "I Want a Room in Loopy Town!". I, too, want a room in Loopy Town.

Speaking of loops, though, we are instead going to talk about the FABRI-TEK Model 8 Add on Core Memory system for the DEC PDP-8/I system – or at least talk around it.

The FABRI-TEK system was an external cabinet that added 24k words to the PDP-8/I system. Most of our discussion of 24k systems has centered on bytes instead of words, but half of these systems have an 8-bit word anyhow. The DEC PDP-8 has a 12-bit word that splits the difference between byte and what became a standard 16-bit word. What 'word' actually means in computing is not as neat an idea as the serious taxonomists would have you believe.

Anyway, memory is implemented with collections of logical gates called 'flip-flops', except for the hundred other ways that it's implemented. 'core memory' is one of those other ways. Actually, it's at least three of those other ways. The FABRI-TEK core memory system represents one of those ways. In this kind of core memory, loops of magnetic material are made to retain either of two magnetic fields and thereby represent two binary states. There's physics behind all of this – handy if ... well handy if a physicist is in the process of explaining it to you.

You can even make core memory at home! All you need is some metallic loops of the right type, some wire, a steady hand, a sewing needle, and some analog electronics. What is harder to understand at home or to have understood at you is that this is all crazy nonsense. It doesn't really matter how a loop of magnetic material stores a binary state. Binary processes are not rare in nature or anthropology. The ancient Hawaiian game of kōnane, played with black volcanic stones and white coral stones, could be used as the basis of a computer memory system if it could be sold for a comparable size, cost, and density. You could use DNA or holograms or toothpaste tubes that are alternately full and empty. Well, obviously you wouldn't put toothpaste back in the tubes to change the memory so that would be more of a write-once system. You could rearrange a particular set of empty and full tubes to represent different information though.

What matters most is how cheap and small the rocks or toothpaste tubes or magnetic cores are. This isn't really a question of physics, or rather it is a series of questions of physics where just about every 'no' answer so far has been wrong. What's the smallest tube of toothpaste? Yes.

Back to core memory. Core memory is fundamentally a textile product. At a time when the computer industry was grasping for remotely affordable technologies for online data storage, textiles were the slice of industry offering volume, density, and low cost. There were decades where choosy consumers might buy a dot-matrix printer able to print around 150 dots per inch but turn up their nose at a set of cotton sheets with more density as measured by thread count. Printer dots per inch is usually measured separately in each axis and thread count is the sum of threads per inch in both.

The breakthrough resolution for the desktop publishing revolution was 300 dpi. That corresponds to a nice 600-count sheet. Run a shuttle through the numbers here and it takes just over 64 letter-size sheets of paper to make a 66" x 96" twin sheet. At the original HP LaserJet's 8 pages per minute, you're looking at around 8 minutes to print a twin sheet. Not bad. That's about the time it might take for a power loom to weave an entire sheet. Of course, the printer performance is based on around 5% toner coverage of the paper and the loom actually weaves the entire thing. A fairer comparison would be a high-speed loom against a printing press. Here, printing technology runs ahead as it eventually did for memory as well, though printed on silicon wafers instead of paper.

By the heyday of the core memory era, the skills and economies that made Hong Kong a postwar textiles powerhouse were weaving little iron beads into computer memory so swiftly that they could produce it for around a cent per bit. The low cost and availability in quantity made magnetic core memory into one of the first really democratic computer memories – available in everything from NCR cash registers to IBM mainframes to Apollo-era space computers. Natural that it would be available even to specialty manufacturers of third-party memory for the DEC PDP-8. In fact, core memory was even used in desktop calculators. One such machine is the Casio AL-1000 – said to be the first Japanese programmable calculator. Perhaps the AL-1000 is the original homesteader in Loopy town!

Automation made magnetic core memory affordable, but so did permissive tariffs. Core memory is classified as 6909.19.10 under the U.S. Harmonized Tariff Schedule, that is to say 'Ceramic wares for laboratory, chemical, and other technical uses' / 'Other' / 'Ferrite core memories'. Other memories received a completely different tariff classification. Dynamic random access memory (DRAM) from Japan and other Southeast Asian countries became subject to complex arrangements that increased their cost in the US by a third or more. A denser magnetic core memory could have seen a second wind had the trade situation deteriorated further.

The winning computer technology at any given moment has often been the cheapest and most widely available, not necessarily the most sophisticated. This was true in 1960 and it's still true today.

This post pairs well with the Tetris theme 'Korobeiniki' / 'Tetris for Game Boy' / Hirokazu Tanaka for Nintendo / 1989.