Sinclair ZX81

In 1980 Sinclair had launched the ZX80, the first computer on sale in the UK for under £100. The ZX81 arrived in March 1981 and took the idea further: fewer components, cheaper to make and more capable.

It was sold in two ways: as a kit, for £49.95, to assemble and solder at home, or ready-built, for £69.95. It was made by Timex in Dundee, Scotland, and in the US Timex sold its own version, the Timex Sinclair 1000, with 2 KB of memory.

The processor is a Zilog Z80A at 3.25 MHz. Much of the logic that was spread over several chips in the ZX80 moved into a single custom chip, the ULA made by Ferranti, leaving the board with very few components.

Standard memory is 1 KB. For bigger programs there was the 16 KB RAM pack, which plugged into the rear port. The 8 KB ROM holds Sinclair BASIC, an evolution of the ZX80's BASIC, written at Nine Tiles by Steve Vickers and John Grant.

The picture is black and white, 32 × 24 characters of text, with block graphics. The processor itself helps generate the picture, so the ZX81 has two modes: SLOW, where the picture stays up while the program runs, and FAST, which is quicker but blanks the screen during calculations.

The ZX81 sold over a million units and was, for many people, their first contact with a computer. The thin black case, designed by Rick Dickinson, and the flat membrane keyboard defined Sinclair's image before the Spectrum.

There were clones in several countries, such as Microdigital's TK82 and TK85 in Brazil.