It is 30 years ago today that Clive Sinclair launched the ZX81, a low-cost computer that seems absurdly primitive by today's standards, but which was one of the first to be cheap enough for anyone to buy and mess around with.

Like many people involved with the UK IT industry today, my first experience of computers was via the ZX81 and its successor, the ZX Spectrum.

The ZX81 was deceptively simple; it consisted of just a handful of chips on a circuit board fitted into a wedge-shaped black plastic case. You could buy it ready-made, or assemble it yourself from a kit, as my father did for my brother and myself.

In terms of specification, the ZX81 does not come even close to the simplest of modern digital devices; it had a 3.5MHz processor and 1kb of memory (yes, you read correctly that's one kilobyte of memory, about one thousandth of a megabyte).

You could only store and retrieve programs by connecting it to an audio cassette tape player, and the keyboard was a flat plastic membrane. It connected to a TV and could only generate a low resolution character-based display in black and white.

Sinclair's genius was in squeezing so much out of so little hardware. It was possible to type in and run programs in the Basic language, despite the fact that the 1kb memory had to hold the frame buffer for the display as well.

The ZX81 also had a crude, but highly effective, way for users to expand it. All of the system bus signals were brought out to a connector at the rear of the case, which made it easy to clip on extra memory modules and the like.

Extra memory was necessary if you wanted to do anything ambitious, and if you had this there were even games available for the ZX81 that used the blocky character-mode graphics to good effect, with a flight simulator and the ground-breaking (for its time) 3D Monster Maze, where the player roamed a simulated maze inhabited by a Tyrannosaurus Rex (see a brief demo of this on Youtube).

The ZX81 wasn't the only home computer around, but as one of the cheapest, it soon caught on, although it didn't sell as well as the Spectrum which succeeded it, bringing better graphics and sound capabilities.

Nevertheless, the device is a milestone in computer history, and one of the ways that many people in the industry today first got a taste of programming and using computers.

05 Mar 2011