The ZX81 was the first computer I owned, and is probably the reason I’m a computer programmer now. It’s a fairly basic machine – black and white, with a character mapped display, but there were some good games on it, memorably Mazogs and 3D Monster Maze.

I learned BASIC on it, but at the time never really got into assembly language or machine code. There were books on the subject, but the tools were rather limited, and saving to tape was notoriously problematic.

The ZX81 was an evolution of the ZX80, with all the logic chips on the ZX80 integrated into a single Ferranti ULA. There were a couple of versions of this ULA; early versions struggled to output a signal on colour televisions due to the infamous lack of a back-porch signal after the horizontal line sync pulse. All Ferranti ULAs run rather hot, so a common mod is to glue on a heat sink.

The basic model came with 1K of RAM, which could be expanded up to 32K externally with a RAM Pack. Tethering a wobbly RAM board off the back of the expansion port was never going to end well if the keyboard was being hammered, hence the expression RAM Pack Wobble.

The board itself is sparsely populated and, like its predecessor, was available in kit form for those hobbyists that either fancied the challenge of assembling their own computer, or wanted to save £20 – the kit was available for an astonishing £49.95 in 1981.

Anyway, enough of that, here’s the computer in all its glory:

  1. Hardware