Manufacturer

Sinclair Research Ltd (UK)

Model

ZX81
(Launched in 1981 and a successor to the ZX80.)

Date Launched

March 1981

Price

£50 as kit without power supply.
£70 complete ready-built.
In February 1984 the kit was selling for a mere £25.

Microprocessor type

Zilog Z80A (or clone) @ 3.25 MHz

ROM size

8 kilobytes

Standard RAM

1 kilobyte

Maximum RAM

16 kilobytes with official expansion pack (as pictured above).
Up to 56K with third-party hardware.

Keyboard type

Flat touch-sensitive membrane

Supplied language

Sinclair BASIC

Text resolution

32 X 24 characters

Graphics resolution

64 x 44 pixels block graphics.
(Made clever use of the character set to achieve this.)

The UK company Quicksilva (started by Nick Lambert in 1980) briefly sold a high resolution graphics board for the ZX81. This gave 256x192 pixels in black and white (see right), contained its own 6KB of RAM, and had commands for plotting points, drawing lines and boxes and scrolling the display. It cost £85, but once the ZX Spectrum came out, with the same resolution plus colour, there was no real reason to expand the ZX81 to hi-res.

Colours available

Monochrome (black on light blue with a colour television)

Example Screenshot

Simple graphics could be produced on the ZX81 by imaginative use of its character set.

Sound

None

Cassette load speed

250 baud

Dimensions (mm)
Weight (grams)

175 x 168 x 40
350

Special features

Single key entry of BASIC commands.
Syntax checking of lines as soon as they were entered.

Good points

The cheapest fully-functional computer available.
Excellent manual supplied.
Adequate version of BASIC which could cope with full floating point arithmetic.

Bad points

Keyboard was very difficult to type on.
No built-in connection for a standard printer.
BASIC was very slow if continuous screen display used.

How successful?

Very popular, around 300,000 were sold in the UK and about 600,000 of the almost identical Timex Sinclair 1000 were sold in the US.

Comments

Very compact and robust design. The printed circuit board only contained 4 integrated circuits:


The Sinclair thermal printer was available for £50.
The ZX81 could do most things that much more expensive models could, albeit not quite so easily.
Autoram Computers in Saudi Arabia even produced a version of the ZX81 which could be programmed in Arabic, including right-to-left text.

A photograph of a ZX81 displaying Arabic text. Image from Sinclair User, February 1984.