ZX81 - Vintage Sinclair

The ZX81 was launched in March 1981 as the successor to the ZX80. It was manufactured in Scotland by the Timex Corporation and was priced at £69.95 or £49.95 in kit form.

Technically, it had very similar capabilities to the ZX80 - a touch sensitive keyboard, monochrome display and 1K of memory as standard. Sinclair's design goal was to be simple and cheap to make, which it was, being 30% cheaper than the ZX80.

To achieve this, the silicon chip count was reduced to only 4 by cleverly combining 18 of the ZX80's chips into a single ULA chip (Uncommitted Logic Arrray). The downside to this is that it got extremely hot due to the electronics being packed so densely. The memory for the Basic language was double that of the ZX80 at 8K. One of the main improvements was the maths package which now could handle floating point numbers and trig functions.

Commercially the ZX81 was a great success and by 1982, 40000 a month were being produced and still could not keep up with demand. A big boost to sales was that they could be bought in the high street through W H Smith stores.
They were also exported to the States in large numbers which boosted the fortunes of Sinclair Research and Clive Sinclair himself who became one of the UK's highest profile bui
businessmen and a millionaire in 1981-82. He was Knighted in 1983.

The ZX81 kick-started a huge interest in programming and computers, and many other computer manufacturers, such as Tangerine, Dragon and Acorn, sprang up to try and capitalise, with varying degrees of success.

Technical details:
Video : Built in RF modulator, monochrome output to a household TV
Display : 24 X 32
Data storage : Cassette recorder
Memory : 1K expandable to 16K
Processor : Z80, 3.25MHz
Operating system : Sinclair Basic
Weight : 12oz

40-key keyboard

Side view showing connections for TV, cassette recorder for data storage and mains adapter.
Note: there was no on/off switch to keep costs down!

A third-party keyboard fitted

Note: PSU on the right side is nearly as big as zx81!