The Sinclair ZX81, released on March 5, 1981, was a hugely successful evolution of the ZX80 and became one of the best-selling home computers in history. Priced at just £69.95 assembled (or £49.95 in kit form), it was the first computer many people in the UK and beyond ever owned, cementing Sinclair's reputation for ultra-affordable computing and fueling the early 1980s home computer boom.
The ZX81 was again the vision of Sir Clive Sinclair, with hardware design led by Jim Westwood at Sinclair Research (formerly Science of Cambridge). The 8 KB ROM containing the improved Sinclair BASIC was developed by Nine Tiles Networks under Steve Vickers. By drastically reducing component count—using only four main chips—the team achieved an even lower production cost than the ZX80 while adding significant usability improvements.
Building directly on the ZX80 experience, development focused on cost reduction and refinement. The ZX81 used a semi-custom ULA (Uncommitted Logic Array) chip to replace 18 TTL chips from the ZX80, enabling a smaller case and lower price. Launched with aggressive mail-order advertising and later sold through high-street retailers like W.H. Smith, it sold over 1.5 million units worldwide. In the United States, it was marketed by Timex as the Timex Sinclair 1000 at $99.95.
The ZX81 was powered by a Zilog Z80A-compatible microprocessor. Key features included:
The minimalist "flying membrane" keyboard and compact black case became iconic.
The 8 KB ROM provided a vastly improved BASIC with floating-point arithmetic, trigonometric functions, and better error handling. Keyword entry remained single-keystroke, and the system supported both SLOW mode (continuous display) and FAST mode (faster execution with flickering). Thousands of programs—games, utilities, and educational software—were published on cassette.
The ZX81's extraordinarily low price brought computing to an unprecedented number of households, schools, and individuals, creating a generation of programmers and enthusiasts in the UK. It inspired a massive software cottage industry and countless magazines. Despite limitations like the wobbly 16 KB RAM pack and membrane keyboard, its accessibility was revolutionary. Succeeded by the color-capable ZX Spectrum in 1982, the ZX81 remains a cultural icon of early personal computing and a prized collectible today.