One and a half million people learned to program computers on the ZX81. It was a fully functional microcomputer with a well developed BASIC operating system and a comprehensive manual. But most compelling of all was its selling price – £49.95 if you built it yourself from a kit, or £69.95 fully assembled.

Conceived by Sir Clive Sinclair as a follow-up to the successful ZX80, it was more powerful and even cheaper. However, demand was so high they couldn’t be made fast enough and production quality suffered. This, surprisingly, did not dampen enthusiasm or dent sales.

The ZX81 was launched in the United Kingdom in March 1981 and manufactured in Dundee, Scotland, by Timex Corporation. It was designed to be small, simple, and above all, inexpensive, with as few components as possible. Video output was to a television set rather than a dedicated monitor. Programs and data were loaded and saved onto compact audio cassettes. It used only four silicon chips and had a mere 1 KB of memory. It has no power switch or moving parts, with the exception of a VHF TV channel selector switch present in some models. It has a pressure-sensitive membrane keyboard. The ZX81’s limitations prompted a market in third-party peripherals to improve its capabilities. Its distinctive case and keyboard brought designer Rick Dickinson a Design Council award.

It was the first inexpensive mass-market home computer to be sold by high street stores, led by W.H. Smith and later by Boots, John Menzies and Currys. The ZX81 marked the point when computing in Britain became an activity for the general public rather than the preserve of business people and electronics hobbyists