Factsheet – Sinclair ZX81


All about the Sinclair ZX81

zx81-pcb For the uninitiated the ZX81 was a small 8-bit home microcomputer invented and produced by Sinclair Research Limited of Cambridge, England. Sinclair Computers (renamed Sinclair Research Ltd. in March 1981) was founded by Sir Clive Sinclair, inventor of the pocket television, the first pocket calculator, the famous rubber-keyed Sinclair ZX Spectrum and later the not-so-popular Sinclair C5 electric car. Fans of this small humble home microcomputer (and there are many of them) will quite rightly tell you that this machine kick-started the UK home computing boom of the early eighties, mainly due to its low price and user friendly attributes.

As its name might suggest, this machine entered the then fledgling home computer market in 1981 as a home-build kit priced at £49.95 and a ready built option at £69.95, following on from the already successful ZX80 (original price £99.95) released in 1979. Sinclair Research managed to keep the price of the Sinclair ZX81 so low by reducing the number of chips on the motherboard from 21 on the ZX80 to 4 on the ZX81. The computer was sold via its traditional method of mail-order (over 300,000 were sold this way by the end of January 1982) and also via the high street with the involvement of W.H. Smith, a British chain of newsagents and stationers. Sales of the ZX81 were huge and by February 1982 Sinclair was producing over 40,000 units per month and still could not keep up with demand. Over a million units were produced within two years of launch.

Sinclair Research teamed up with Timex in the US to produce the Timex Sinclair 1000, a version of the ZX81 for the North American home computer market, which sold in considerable numbers and was manufactured by Timex in Dundee, Scotland.

ZX81 Specifications

The ZX81 used a completely re-designed main board with a much reduced chip-set (from 21 chips on the ZX80 to 4 on the ZX81) mainly due to a new CPU which replaced 18 chips on the ZX80 main board. The ZX81 had no sound chip or speaker and had monochrome output to a UHF TV set via an RF Modulator. Data was transferred to/from the ZX81 via 3.5mm jacks and a normal audio cassette player. Power input was from a custom Sinclair 9V DC transformer.

Depth – 167 mm (6.32 in)

Height – 40 mm (1.57 in)

Weight – 350 grams (12.15 oz)

CPU – Z80z at 3.25 MHz

Display – 24 lines x 32 characters (text), 64 x 44 pixels graphics mode

ROM – 8K with BASIC interpreter

RAM – 1K internal, externally expandable to 16K

Power – 420ma at 7-11V DC

Software for the ZX81

A large amount of software was produced for the Sinclair ZX81, ranging from home business software to the games we wasted our youth on! It was the time of the bedroom-coder, a new breed of computer programmer who produced software from home and either marketed and produced the finished article themselves in small scale operations, or sold the code to a larger software publishing house for a one-off payment or royalties. It would be impossible (at least too time consuming) to list all of the software ever produced by every individual and software house here on this site, instead I have elected to choose some of the biggest software houses of the time and list their most popular titles. There are obviously other big names such as Artic that have been omitted for now and may be added at a later date.


sinclair-soft-flowSinclair Research teamed up with several software houses to produce their own-brand software for the Sinclair ZX81. The most prolific of these was to be Psion and ICL (International Computers Limited), with a small range of business, educational and entertainments titles following. Also worth mentioning is the Sinclair Learning Lab (a set of 12 training software cassettes in a ring binder) and a small range of multi-title software cassettes released by Sinclair with black and red inlays matching the packaging style of the Sinclair ZX81 itself.



jkgreye-soft-flowJ.K. Greye were responsible for possibly the most famous Sinclair ZX81 game of all time – 3D Monster Maze, one of the first games on a home micro to be in first person perspective. This title followed on from the successes of their previous multi-title releases and Catacombs, a multi level graphical adventure. They later became New Generation Software and sported a new full colour look to their inlay graphics.



qs-soft-flowSome of the best looking inlays were to be found on Quicksilva games, and luckily the games themselves were some of the greatest arcade game ports you could find on the Sinclair ZX81. QS Asteroids, QS Defenda, Galaxians, and QS Invaders were amongst these titles some of which were supplied unusually with a set of memory addresses that you could ‘POKE’ so that the game could be modified to your liking! Unlimited lives anyone?



sfarm-soft-flowOK, so not necessarily a big software house but regarded by many as one of the best for finally producing what all Sinclair ZX81 fans had dreamed of – high resolution software. The end result was Sinclair ZX81 software that ran at the same resolution as its replacement, the Sinclair ZX Spectrum albeit without colour or sound.

Author: Ant Harper

Father, Husband, website developer, avid gamer since the mid-70s and collector of just about anything video game related. 8-Bit microcomputer and Sinclair specialist with a huge Sinclair related collection of his own. Blogs about retro gaming here but occasionally elsewhere when people ask. Bored of Mario and never much liked Zelda. Performs quirkafleegs for cold hard cash. Often found destroying ice crowns in the Lands of Midnight. Remembers: Lunar Lander. Plays: Steel Battalion, Gears of War

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  1. Superb write up here and great pics too. Enjoyed reading through it. Brought back a lot of memories and updated my memory on what I thought was a measly 1mhz processor but in fact was a whopping 3mhz processor! haha

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