DB … Cooper?
I know the names for the tradespeople who cut meat, who make bread, who dip candles. When you say that the cobbler’s children are poorly shod, I know what you mean. I‘m familiar with the various smiths and wrights and mongers. I know it’s the fish mongers who sell the fish and it’s the fish smiths who make sushi. I don’t know the name for the trade that designs and builds electronic connectors but I think it’s cooper. After all, inline coaxial connectors are often called barrels.
One such famous coopering firm was Cannon. This is not the Japanese Canon who designed the TypeStar we featured at the end of last year, though Cannon designed the DE-9 serial connector for that machine.
(Imagine that the paragraphs where I just made barrel jokes were here, but then edited out in keeping with my New Year‘s resolution to be more serious, or at least more concise.)
By the end of the Second World War, Cannon connectors were ubiquitous in both aerospace and the motion picture industry. What these industries have in common is that they were both centered in Southern California.
Along came the computer industry, and with it a need for ever denser, ever smaller connectors. Though the computer industry was then rooted in places like Pennsylvania, New York, Indiana, Minnesota, Massachusetts, and Texas, builders found that the ‘D’-shaped subminiature connectors designed by Cannon fit the bill perfectly. Like many barrel makers, Cannon was more concerned with the outside of the barrel than what went inside it, or through it in the case of data connectors. The ’D’-shaped subminiature connectors (often called D-sub) came in several sizes, though Cannon opted against the traditional barrel sizing lexicon (Tun, Butt, Hogshead, Barrel, Kilderkin, Firkin, etc) and favored the Roman over British with sizes D, C, B, A, E. Real empires do you an alphabet, not just a jug.
Within a D connector shell size, pins could be arranged any way a customer wanted, though several variants quickly dominated. See, the reason to build a connector is to connect something. If you want it to be connected by a cable and your specialty is not high-quality cables (hint: if your specialty is anything but cables, then it’s not high-quality cables) then it would be great if you buy pre-made, tested cables off the shelf. That means that your cablewright/cablemonger has a role in choosing your connector. Common connectors based on the D shells were DB-25 (used for some serial and SCSI ports, for instance), DA-15 (used for Ethernet AUI), DE-9 (widely used for serial, though often incorrectly called DB-9. An unshielded plastic variant was used for many Atari-style joysticks and the Canon TypeStar). The number denotes the number of connectors inside the shell. The lead image for this post shows a DB-13W3 connector with 13 regular pins and three coaxial connectors for video. I remember such connectors from Sun Workstations.
My goal was to do a series on each DB-25, DA-15, DE-9, and DB-13W3 in the years 2025, 2115, 2109, and 2113W3 respectively but I realized that I could bring the DB-25 series forward a century and maybe do part of it this year.
I’ll start with the DB-25 connector on the IBM Printer Adapter for the original IBM PC. Intended originally for connection to printers, this parallel data port was easily adapted to many other peripherals that could be implemented with a 8-bit-out / 4-bit-in interface. This adapter was very, very easy to program. It was so simple, however, that it lead to a number of very simple implementations on the peripheral side that were very timing sensitive. If you weren’t in a position to manipulate the pins on your side in real time, the whole thing could become frustrating very quickly. In practice, this was possible only when the PC was doing absolutely nothing else.