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 as a result was 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.
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.
In an Electronics Times article from 18 February 1982 it writes "The ZX81 is selling at the rate of 60,000 a month, two thirds for export, and Timex is producing one every 10 seconds at its Dundee plant. Sinclair said he had sold more than 300,000 units, making it the biggest selling personal computer.'
The ZX81's successor, the ZX Spectrum, was released in April 1982. The ZX81 was discontinued in 1984.
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