Happy Birthday ZX81

30 years ago today the Sinclair ZX81 was launched, and the impact it made forged the future of 1.5 million geeks. Costing about as much as a cheap netbook would cost now, you could buy it in built up and ready to go for £69.95 in 1981 money or as a kit for 20 quid less. With four chips, two transistors, a dozen or so each resistors and capacitors and a handful of other bits, someone with a steady hand and reasonably good soldering could put it together in a day. When people talked about "building a computer", they meant building a computer...

Just to hold up some scale, Roxy Music's cover of "Jealous Guy" was at number 1, but would be ousted by Shakin' Stevens' "This Ole House" a week later. Joe Dolce's "Shaddapa You Face" had kept Ultravox's "Vienna" away from number 1 (there's no justice in the world) and Depeche Mode had released "Dreaming of Me" - it would be a couple of months before "New Life" would drive synth-pop maddeningly into our minds. Look at a Youtube clip of them around then, they're all so young and have no idea what's about to hit them. The last Triumph TR7s were being made, and the first DeLorean DMC-12s were being sold. STS-1, the maiden voyage of the space shuttle Columbia, was still five weeks away.

I got my ZX81 a little later in the year. As with many people around Dundee at the time, everyone's dad "knew a man" who could acquire one without all the usual supply chain hassle. They were built at the Timex factory near the Kingsway (it's a big ASDA now), and rejected units found their way from the bins to people's bedrooms via nearby pubs - with a quck stop-off to repair whatever minor fault had dropped them off the assembly line. Later, when the ZX Spectrum was launched in 1982, exactly the same thing would happen. You can't help but wonder if the booming computer games industry in Dundee got all its local talent because everyone - and I mean everyone - had a ZX Spectrum to hack on...

So, why was the ZX81 so influential? Well, the cost made it more accessible than other machines of the day (if I recall correctly, it was the first home computer that we would recognise as such that cost less than £100). The hardware was well documented, with a fat manual that described the function of all the system variables for the BASIC interpreter and listed all the Z80 machine-code instructions alongside the not-ASCII character codes (the ZX Spectrum would switch to a modified ASCII character set). Oh, and it had the pin-outs for the expansion connector on the back.

Ah yes, the expansion connector. Where you could stick in a 16k RAM pack (with the dreaded "RAM pack wobble", where the edge connector fingers didn't make good contact and the slightest touch would make it crash). The ZX Printer, which used a tiny spark to burn away the surface of aluminised paper giving very space-age black-on-silver printouts (if it hadn't got damp and oxidised). Joystick interfaces, parallel and serial ports, even disk drives (one enterprising chap has devised an IDE interface for the ZX81 - not hard, since IDE is just a fast parallel port. One disk block could hold the whole unexpanded RAM of a ZX81) and network interfaces! The electronics magazines of the day were full of articles on using a ZX81 to control your central heating, or a robot, or an automatic greenhouse waterer, or make electronic music with an add-on board containing another old stalwart, the AY-3-8192. Manufacturers like Cheetah, Memotech (who went on to produce their own MTX range of computers), dK'tronics and Datel as well as many more little "one-man band" companies produced goodies to plug into your ZX81. There's still a company that makes games console controllers and cables called Datel, but I don't know if they're the same guys.

A couple of the manufacturers stand out among them. Memotech not only produced their not-quite-MSX MTX500 and MTX512 computers (a hefty aluminium extrusion with a keyboard even more solid than the IBM Model M I'm typing on), but they also had a stackable expansion system for the ZX81. You plugged a kind of docking station into the expansion port, which locked in place with a plastic tab that raised the ZX81 slightly and was held in by two of the case screws. This held 16k of RAM and had a Eurocard-like socket on top, to which you added other modules like a sound interface, printer interface, more RAM (up to a whopping 64k!) and a high-res graphics unit that let you plot on a 256x192 framebuffer. Another manufacturer, dK'tronics, got round the lack of user-programmable graphics by selling a "4K Graphics ROM" that plugged into the back, and had alternate character sets for Space Invaders, Pacman, Defender and other types of games that could be switched in by appropriate software.

We can do a lot of really cool stuff with computers now, but they just somehow don't seem as fun as something you could take to bits and solder in your bedroom. Maybe that's why things like Arduinos have taken off in such a big way. Maybe we need stuff that you can fix with a crappy Maplin iron while listening to Soft Cell.

Posted by gordonjcp on March 5, 2011