Sinclair ZX81

Vital Statistics

Introduced March 1981
Retired: 1982
Price: £49.95 (in kit form), £70 (ready-assembled)
Quantity Sold: approx 1,000,000
Countries: UK and Europe (in USA, Timex-Sinclair TS1000)
Dimensions: 167 x 175 x 40 mm
Weight: 350g
Ports: Z80 bus, tape, video, PSU
Usable RAM: 1K (expandable to 64K)
Built-in ROM: 8K
Colours: 2 colours (black and white)
Text: 32 x 24 characters (8x8 pixels each)
Graphics: 256 x 192 pixels
Sound: none
Built-in Language: Sinclair BASIC
Clones: TS-1000 (USA), Lambda, PC-8300, Power 3000 (Hong Kong)

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What's it like today?

Fun Factor:
: Fairly common
Typical value: £30
Boxed & Mint: £80


Work on the ZX81 hardware began in September 1979, even before the launch of the ZX80, but it was the development of the uncommitted logic array, or ULA, which allowed the machine to go into production. The ULA, produced by Ferranti for Sinclair, reduced the chip count and brought the retail cost of the machine, in kit-form, down to £49.95.

As with the ZX80, Nine Tiles was called upon to provide the new BASIC, but this time there was 8K to play with. Steve Vickers, who had joined Nine Tiles in January 1980, added the floating-point arithmetic, including trigonometric and other functions. "As far as Clive was concerned, it wasn't a question of what the machine ought to be able to do, but more what could be crammed into the machine given the component budget he'd set his mind on," said Vickers in an interview on July 23, 1985. "The only firm brief for the '81 was that the '80's math package must be improved." The ROM was almost complete by the end of autumn 1980, but support still had to be added for the ZX Printer. Somewhere between this time and the launch, a bug crept in which caused the square root of 0.25 to be 1.3591409. Nine Tiles quickly fixed the bug, but Sinclair was somewhat tardy in making this version available to people who had already bought the machine.

The Sinclair ZX81 replaced the ZX80 in February 1981. This new machine now provided SLOW and FAST mode, which meant the ZX81 was capable of executing a program and writing to the screen at the same time (SLOW mode). The ZX80 only had FAST mode which could not do this. The 4K ROM included 30 new functions plus some new instructions to control a printer.

Because of better componentisation, the ZX81 was able to be sold for £30 less than the outgoing ZX80.

The ZX81 was well received and became a massive success, spawning a series of clones, both illegal and licensed by Timex, which was manufacturing the UK models for Sinclair at its Dundee plant. Inspired by the public reaction to the ZX81, and annoyed at not winning the contract to design a computer for the British Broadcasting Corporation, Sinclair decided the market needed a budget colour computer.

The ZX80 and ZX81 hardware had been the primarily the work of one man; Jim Westwood, but he had been moved to the flat-screen television department, so the hardware design job on the machine which became the ZX Spectrum, was given to Richard Altwasser, while at Nine Tiles, Vickers was again asked to provide the BASIC for the Spectrum.

The US version of the ZX81 was marketed by Timex-Sinclair, called the TS1000. This varied only slightly, with 2K RAM instead of 1K, a shielded case, TV output on channels 3 or 4, and the screen was black on light blue background, instead of a white background.

ZX81 News

06 March 201810 PRINT "ZX81 at 37" 20 GOTO 10

Over 40? You've used one of these. Of course you have

The ZX81 was launched 37 years ago this week as a £49.95 kit (£69.95 assembled) and introduced an entire generation to the joys of computing, fights over the family television and prodigious use of sticky tape.

Click here to read the full article

15 May 2016New 1K Hi-Res ZX81 games

Johan "Dr Beep" Koelman's been in touch, informing us of a bunch of new 1K Hi-resolution ZX81 games he's been working on.

After Q-bert (2013), four new games have been coded in 1K hires in 2015 and 2016, with one still a work in progress:
The Edge - The Edge is a 1 player cardgame where chance will finish you the game or not. 52 hires cards, board and gameplay in 1K.
Marble Racer - Marble Racer is a racing game with drifting through corners. Race 5 rounds a.s.a.p.
Roadracer - a simplified version of Grandpr1x for the ZX Spectrum. In 1K a 3D view on a racetrack and goal to drive 2 rounds as quickly as you can. Hitting the side of the track will stop the car.
2D Monster Maze - a spin-off of 3D Monster Maze. After a day at the fair with no visitors Rex must be fed manually. Find the food before becoming the food. If the suspense won't kill you, Rex will.

In progress: Asteroidbelt - A classic starship travel through space avoiding asteroids.

All of the above are available free for download from Sinclair ZX World.
Thanks Johan!

01 April 2016Hopper - ZX81 Retro Review by Steve Trower

In the early 80s, when video games were just starting their migration from the arcades to the living room, it was common for games programmers to take their inspiration from the more popular arcade games, and so we ended up with a million and one variations on Pac-Man, Space Invaders, and Frogger - and landing fairly obviously in Frogger's pond is Hopper, released for the 16K ZX81 by Personal Software Services (PSS) in 1982.

Click here to read the full article

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This page was last updated on 22nd April 2014.