Posted on April 8th, 2010 1 comment
The Sinclair ZX81 (a.k.a. Timex Sinclair 1000) could be the most underpowered personal computer in history that boasted a very active commercial games scene. It produced a strictly black-and-white display and had no sound hardware. It shipped with a whopping 1K of memory, about 672 bytes of which was usable as program space. You could expand this with a 16K RAM upgrade that didn’t attach firmly to the ZX81 and therefore crashed the computer frequently. Since there was no dedicated video chip, the CPU had to spend nearly three-quarters of its time drawing the TV image on the fly, in an arrangement sort of like what Atari 2600 programmers had to deal with. The BASIC language included was pretty powerful, but had assorted bugs — the first version of it thought the square root of 0.25 was 1.3591409. Graphics were limited to the system’s built-in character set, which included letters, numbers, a handful of symbols, but no apostrophe (though people found workarounds for this later on).
But that didn’t deter British coders. One of them produced a full chess game in 1K — a very bad chess game, but one that’s astonishing simply because it works at all. 16K quickly became a base requirement for ZX81 gaming, though, and developers across England released action games, sports management sims, really rudimentary 3D titles, and so on. The aptly-named zx81stuff.co.uk has archived a fair bit of these releases, but many are still missing in action, advertised in magazines but not known to exist anywhere at this point. Shame.
I waned to show off Planet of Death because it so egregiously shows another challenge ZX81 coders faced. Since the computer’s video signal was generated by the Z80 processor, whenever you overtaxed the system with too resource-intensive a program, you ran the risk of having the screen go all wonky and flickery. Programmers had the option of turning off video output entirely to let the CPU devote all its time to running code instead, which is what Artic Computing seems to have done for this adventure game. A lot. After every single keypress, in fact. The resulting mess is somewhat mitigated by the fact that there’s no way you could touch-type on the ZX81’s membrane keyboard, so you couldn’t type faster than what’s shown in the video anyway.
The game, the first of eight adventures Artic produced for the ZX machines, reminds me a lot of Mystery House and the other super-simple games Ken and Roberta Williams got their start with. Like those adventures, Planet of Death has no real plot development and is basically a series of item-ferrying puzzles with an arbitrary maze stuck in the middle. Enjoy the flicker, nonetheless.