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Happy 30th Birthday, Sinclair ZX Spectrum

The story of an historic micro

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Design cues

Dickinson's design for the computer itself originally called for a more angular, wedge-like look that took cues from the ZX81 - again reinforcing the notion that Sinclair viewed the Spectrum simply as an upgraded ZX81. The new machine's design began to be sketched out early in August 1981.

By the middle of the following month, Dickinson's sketches show something more like the final look: a flatter design with a raised rear section and rounded sides, though at this stage these were formed from angles rather than a smooth curve. The rear area also dipped from the sides to the centre.

Sinclair ZX81 Colour design sketch

Rick Dickinson's 11 August 1981 early ZX81 Colour design concept
Source: Rick Dickinson

The 'tweaked ZX81' concept would not survive, at least not from a marketing perspective. Sinclair would soon position the Spectrum - the new name undoubtedly part of the rebranding effort - as a more advanced machine than a mere upgrade.

After the Spectrum's launch, in an interview with Sinclair User magazine published in July 1982, Dickinson would say: "[The Spectrum] is a step upmarket, and I was really trying hard for a super-smart machine. It is not for quite the same amateur market [as the ZX81]."

Dickinson would leave Sinclair in 1985, after which he formed his own design agency and went on to devise the look of the Z88, the portable computer Clive Sinclair created in the late 1980s at his new firm, Cambridge Computers.

Sinclair ZX Spectrum sketch

The design begins to take shape in a sketch dated 15 September 1981
Source: Rick Dickinson

Back to Basic

But while Dickinson was working on the Spectrum during 1981, coder Steve Vickers was revising Sinclair Basic and the core OS at Nine Tiles Software. Nine Tiles had been hired to write Sinclair Basic for the ZX80 back in 1980 and was the natural choice to update the code for the ZX81. That was Vickers' task, then a fresh employee, and he penned the ZX81's manual too. During 1981, he added colour and sound commands to ZX81 Basic, as requested by Sinclair. The character set was extended with the addition of lower-case letters.

But Vickers also added multi-statement lines of code and other innovations in an attempt to make the Spectrum something more that a ZX81 with more memory, a better keyboard and colour bolted on. He significantly upped the data transfer rate to and from cassette tape, and in addition to programs, array variables - to enable primitive databases - and blocks of memory could be saved to tape.

Sinclair ZX82 final design

Early 1982 and the design is there... but not the name
Source: Rick Dickinson

Indeed, Vickers and his Nine Tiles colleagues had initially hoped to write the Spectrum's Basic interpreter from scratch in order to eliminate inefficiencies in the older code and make it run more smoothly. But Sinclair's tight schedule made this impossible. Vickers' views were ultimately justified: Basic programs ran slowly on the Spectrum.

"The Basic is slow," wrote Computing Today in August 1982. "Well, 'snail-like' would be a better description. The last test was done with a loop of 100 instead of 1000 as I thought that you might like to read the review before the Christmas holidays."

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