page_title: ZX81
section_title: Peripherals and software
hierarchical_section_title: ZX81 / Peripherals and software
caption_attribution_description: ZX81 with 16 kB RAM pack and ZX Printer
context_page_description: The ZX81 is a home computer that was produced by Sinclair Research and manufactured in Dundee, Scotland, by Timex Corporation. It was launched in the United Kingdom in March 1981 as the successor to Sinclair's ZX80 and designed to be a low-cost introduction to home computing for the general public. It was hugely successful; more than 1.5 million units were sold. In the United States it was initially sold as the ZX-81 under license by Timex. Timex later produced its own versions of the ZX81: the Timex Sinclair 1000 and Timex Sinclair 1500. Unauthorized ZX81 clones were produced in several countries.
  The ZX81 was designed to be small, simple, and above all, inexpensive, with as few components as possible. Video output is to a television set rather than a dedicated monitor. Programs and data are loaded and saved onto compact audio cassettes. It uses only four silicon chips and a mere 1 KB of memory. There is no power switch or any 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.
context_section_description: The success of the ZX81 led almost immediately to enthusiasts producing a huge variety of peripherals and software. Clive Sinclair was "amused and gratified" by the attention the machine received but other than what Clarke described as "a few remarkably poor programs on cassette" made little effort to exploit the demand, effectively ceding a very lucrative market to third party suppliers, a decision that undoubtedly forfeited a lot of potential earnings. W.H. Smith, for instance, was able to exploit a peculiarity of the ZX81; owners found that technically obsolete low-fidelity mono tape cassette recorders worked better as storage devices than higher-quality music systems. Smith's purchased cheap "shoebox" cassette recorders in the Far East and sold them with the W.H. Smiths logo as "data recorders". Over 100,000 were sold in 18 months.
  Sinclair released only two official peripherals for the ZX81, a 16 KB RAM pack (actually the same one previously released for the ZX80, but rebadged) and the ZX Printer, both of which plugged into the edge connector at the rear of the ZX81. They retailed at a launch price of £49.95 each but both had notable flaws. The RAM pack was top-heavy and was supported only by the edge connector. It had a habit of falling out of its socket at crucial points and crashing the ZX81, losing anything that the user had typed in. Users turned to using sticky lumps of chewing gum, double-sided tape or Blu-Tack to cure what became known as the "RAM pack wobble" problem. The ZX Printer was a tiny spark printer that used two electrically charged styli to burn away the surface of aluminium-coated paper to reveal the black underlay. It worked reasonably well at first but its output deteriorated rapidly after a time.
  Many non-Sinclair peripherals aimed to remedy the ZX81's flaws and provide many new capabilities. These included RAM packs providing up to 64 KB of extra memory and promising to "fit snugly ... giving a firm connection" to the computer, typewriter-style keyboards, more advanced printers and sound generators, and even a hard disk interface, which Clive Sinclair thought was "quite overgilding the lily". A wide range of software was also published. Within only a year of the ZX81's launch, around 200 independent companies had been established to manufacture and sell Sinclair-compatible hardware. The people behind the ZX81 cottage industry were very often not computer professionals but were, as the Financial Times noted, "school teachers, civil servants, electrical engineers and technicians [who] have set up small operations in their own time".
  The ZX81's popularity was publicly demonstrated in January 1982 when civil servant Mike Johnstone organised a "ZX Microfair" at Westminster Central Hall. Seventy exhibitors set up stalls with only a few hundred visitors expected in a hall with a capacity of 650 people. More than 12,000 people came and the police had to control the crowd. Thousands, many of whom had travelled long distances, queued outside for up to three hours to get into the hall; Clarke, who was only able to enter after identifying himself as a journalist, wrote that "no one knows how many gave up in despair". The exhibitors sold thousands of pounds' worth of software and hardware "as fast as three pairs of hands on each stall could hand them over and stuff the fivers into improvised overflowing cash boxes", he added. The fair also showed Sinclair Research's relatively unimportant role in the computer's success, with only small crowds at its booth compared to the "rugby scrum" elsewhere. By August 1983 seven more ZX Microfairs were held.
  Thousands of ZX81 programs were published, either as printed listings that could be typed in or as ready-made applications that could be loaded from cassette tape. Many computer magazines featured ZX81 program listings – some, such as Sinclair Programs, were dedicated entirely to listings – while many individuals became the archetypal "bedroom programmers", producing games and applications which they produced, marketed, recorded, and sold from their own homes. Som
caption: A ZX81 connected to Sinclair's official peripherals – the notoriously wobbly 16 KB RAM pack and the ZX Printer.
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