Editing ZX81 (section)

== Peripherals and software ==
[[File:ZX81 - rampack - ZX Printer.jpg|right|thumb|A ZX81 connected to Sinclair's official peripherals – the notoriously wobbly 16&nbsp;KB RAM pack and the ZX Printer|alt=ZX81 computer with a 16&nbsp;KB RAM pack and a ZX Printer attached]]
[[File:ZX81-16K-RAM.png|right|thumb|Closeup view of the 16K RAM module, showing its edge connector]]
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<ref name="Hayman" /> but other than what Clarke described as "a few remarkably poor programs on cassette",{{r|Clarke}} his company 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.{{sfn|Adamson|Kennedy|1986|p=112}}

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Sinclair released only two official peripherals for the ZX81,{{r|Clarke}} a 16&nbsp;KB RAM pack (actually the same one previously released for the ZX80, but rebadged) and the [[ZX Printer]], both of which plug into the edge connector at the rear of the ZX81. They retailed at a launch price of £49.95 each but both have notable flaws. The RAM pack is top-heavy and supported only by the edge connector. It falls out of its socket at crucial points and crashes the ZX81, losing anything that the user has 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.{{sfn|Adamson|Kennedy|1986|p=96}} The ZX Printer is a tiny [[spark printer]] that uses two electrically charged styli to burn away the surface of aluminium-coated paper to reveal the black underlay. It works reasonably well at first but its output deteriorates rapidly after a time.{{sfn|Adamson|Kennedy|1986|p=107}}

Many non-Sinclair peripherals aimed to remedy the ZX81's flaws and provide many new capabilities. These included RAM packs providing up to 64&nbsp;KB of extra memory and promising to "fit snugly&nbsp;... giving a firm connection" to the computer,<ref>[[#BYTEJune1982|''BYTE'' (June 1982)]]</ref> typewriter-style keyboards, more advanced printers and sound generators.{{sfn|Dale|1985|p=108}} 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.<ref>[[#Kewney|Kewney (3 May 1982)]]</ref> 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".<ref name="FT 20 Mar 1982" />

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. Tens of thousands, mostly youths, came from around Britain, and the police had to control the crowd. They queued for three hours around the hall, with a group of 50 entering as another group left. About 12,000 entered 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 [[Banknotes of the pound sterling|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.<ref name="FT 20 Mar 1982" /><ref name="Clarke">[[#Clarke|Clarke (11 February 1982)]]</ref> By August 1983 seven more ZX Microfairs were held,<ref name="zxmicrofair8">{{cite web |title=The 8th ZX Microfair Showguide |publisher=Retrogames |url=http://www.retrogames.co.uk/016196/Sinclair/The-8th-ZX-Microfair-Showguide |access-date=23 February 2014}}</ref> with the 14th ZX Microfair at [[Alexandra Palace]] in November 1984, still organised by Johnstone.<ref name="crashxmas8485zxmicrofair14">{{Cite magazine |title=The 14th ZX Microfair |magazine=Crash |date=December 1984 |issue=12 Christmas Special 1984/85 |url=https://www.crashonline.org.uk/12/news.htm}}</ref>

[[File:ZX81 with modified keyboard.jpg|left|thumb|Many ZX81 owners replaced the machine's touch-sensitive keyboard with more usable add-on keyboards produced by third-party suppliers.]]
Thousands of ZX81 programs were published, either as [[type-in program]]s or as ready-made applications that could be loaded from cassette tape. Many computer magazines featured ZX81 program listings&nbsp;– 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. Some went on to found their own software houses, employing teams of programmers&nbsp;– some still at school&nbsp;– to produce programs for the ZX81 and other computers. Existing companies also sold software; [[Psion (computers)|Psion]] produced a series of ZX81 programs in close association with Sinclair, including a flight simulator,{{sfn|Morris|2007|p=20}} while [[International Computers Limited|ICL]]'s range of ZX81 programs sold over 100,000 cassettes in less than three months.<ref name="ET-interview" /> Psion's success with the ZX81 had a profound effect on the future of the company. Its work on the ZX81 database program ''Vu-File'' led to Psion switching its focus to the development of [[personal digital assistant]]s, which resulted in the launch in 1984 of the [[Psion Organiser]], the world's first handheld personal computer.{{sfn|Bridgewater|Doyle|1998|pp=156–157}} Some of the most popular ZX81 games (Psion's [[Flight Simulation (Psion software)|''Flight Simulation'']] being an example) were rewritten for the Spectrum to take advantage of the newer machine's colour and sound capabilities.

Enterprising programmers were able to produce games for the ZX81 using nothing more than text characters and the machine's limited [[text semigraphics]]. Some ZX81 games achieved lasting fame, such as ''[[3D Monster Maze]]'', a tense first-person perspective game that involved the player escaping a labyrinth with a ''[[Tyrannosaurus rex]]'' in pursuit. Written in a combination of BASIC and [[machine code]], its innovative design led it to be hailed as the first home computer 3D game and a landmark in the [[history of computer and video games]].<ref>[[#SU0484|''Sinclair User'' (April 1984)]]</ref>

One of the more bizarre software products for the ZX81 came about as a result of music companies attempting to capitalise on the popularity of Sinclair's computers. In 1983, [[EMI]] released a single by [[Chris Sievey]] that had a ZX81 program recorded on the B-side. [[Island Records]] responded with ''[[XL1]]'' by [[Buzzcocks]] frontman [[Pete Shelley]], packaged with a program for the ZX Spectrum.<ref>[[#YS0384|Munford (March 1984)]].</ref>