Sinclair ZX81 Kit

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The ZX81 was launched on 5th March 1981 by Clive Sinclair as the successor to the ZX80, with a larger memory and improved mathematical functions. It was available ready-built (£69.95) or in kit form (£49.95). It was extremely popular due to its low cost and relative power, and hence well supported with software and peripherals by both Sinclair and other companies. The ZX81 was also extensively used in schools and colleges for educational purposes, many people working in the computer industry today had their first computer experiences with the ZX81. It was also the first mass-market home computer that was available to buy in high street shops like W.H. Smiths.

The kit contained all the necessary parts, including keyboard, case, printed circuit board, resistors, capacitors, connectors, integrated circuits, power supply, cables etc. When completed the computer can be used on UHF Channel 33 of any Black & White, or Colour TV. It is possible to use the computer on UK (50 hertz) and US (60 hertz) televisions by setting a ‘jumper’ on the circuit board. 

In the advertising of the ZX81, Sinclair boasted that the higher specification and lower price were a result of design. The ZX80 had reduced the chips in a working computer from around 40, to 21. The ZX81 then reduced that number to 4. The ZX81 was based around the Z-80A CPU which ran at 3.5MHz. It came with 1K of RAM, and 8K of ROM providing a simple BASIC interpreter. The other chip was an uncommitted logic array (ULA) chip from Ferranti which Sinclair advertised as their unique, custom-built, "master chip" which replaced 18 ZX80 chips. 

The RAM could be expanded externally to 16K with the 16K-byte RAM pack. The memory can be expanded externally to a maximum 64K, although this replaces rather than supplements the on-board memory. With only 1K of RAM and 8K of ROM, the ZX81 was not capable of colour graphics. However, it did not stop the sales of this machine, which sold over 1.5 million units.

The case was designed by Rick Dickinson, the in-house industrial designer at Sinclair Research Ltd. In 1981 the ZX81 won a British Design award. The computer was physically quite small measuring 167mm deep by 40mm high. The slim plastic case included a membrane keyboard and a single circuit board. The entire machine weighs just 350 grams.

The ZX81's successor, the ZX Spectrum, was released in April 1982. The ZX81 was discontinued in 1984.

Our kit is unmade and comes with the original polystyrene box.

Manufacturer: Sinclair
Date: 1981

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This exhibit has a reference ID of CH21611. Please quote this reference ID in any communication with the Centre for Computing History.


Sinclair ZX81 Kit

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