He was convinced his ZX Spectrum would outperform rivals, such as the BBC Micro and Commodore 64, in the nascent market for computer hobbyists. "We believe the BBC makes the best TV programmes and that Sinclair makes the best computers," he declared.
But even Sinclair can have had no idea he was about to set in train an explosion in computing that would pave the way for games consoles, such as Nintendo's Game Boy and Sony's PlayStation.
The Spectrum came with 16k of computer memory (upgradeable to 48k) - an amount that now seems risibly small - and a basic price of 125. Computer hobbyists immediately realised that they could use its computer language, BASIC, to write games that took full advantage of the machine's full-colour, high-resolution graphics and soundcard. The name - Spectrum - reflected the new eight-colour capability missing on the earlier ZX80 and ZD81 models.
The technology sounds primitive considering the average PC now has more computing power than it took to fly the Apollo missions to the Moon.
The Spectrum was born into a computing world where users - who really needed to be enthusiasts - typed command-line entries in green letters on a black screen in order to get their computer to run basic operations. Microsoft Windows did not exist and there were no desktop icons to click.
Fans of Sinclair used the machine to write pioneering games with moving colours and "whizzy" sound. To play them, ZX owners needed a cassette player, since games were on tape. A plug-in joystick navigated spacecraft, cars and characters through computerised obstacles. The chip inside, the Z80, was the same as the one that powered Pac-Man machines in amusement arcades. Experts agree that bringing the world of the arcade into the home was the Spectrum's single biggest achievement.
Quentin Cutts, a senior lecturer in computer science at Glasgow University, said: "The Spectrum
came out in the era of a real change from hobbyist computer-builders to games-machine users. We moved from an era where users could build their own games to an era where it became a consumer product."
Millions of units were sold worldwide and the Sinclair Spectrum went through several upgrades. But the seeds of its demise were already being sown in the mid-1980s as the computer revolution gathered pace. In California, Apple was working on a colour display screen featuring objects the user simply clicked on - a graphical user interface - that would truly turn the home computer into a mass-market product due to its sheer simplicity. Microsoft was also hard at work on its own operating system, Windows, that would eventually run 90 per cent of the world's PCs and mimic the graphical point-and-click system popularised by Apple.
Sir Alan Sugar's Amstrad sought to take market share from both Commodore and Sinclair by launching its first mass-market PC in 1984. In 1986, it bought Sinclair's company, which had attempted, unsuccessfully, to win over the business market with a new version of the Spectrum.
Nintendo's Game Boy - launched in 1989, and the first pioneering version of the PlayStation in 1991 - proved the final nail in the Spectrum's coffin.
SINCLAIR VERSUS MODERN-DAY MACHINE
Processor: Z80A 3.5MHz.
Memory: 16kb upgradeable to 48k.
Weight (computer only): 19oz.
Graphics: 256x192 resolution, capable of producing eight colours at two brightness settings, creating 15 shades. Text displayed in 32 columns in 24 rows of characters.
Sound: produced by a one channel beeper on the machine.
Software: packages available on audio cassette.
Hardware: raised rubber keyboard and portable TV monitor.
Ease of use: Users required to know BASIC, a computer programming language.
Dell Home Essentials Dimension E521 (typical mid-range desktop PC)
Processor: AMD Athlon 64 1,000 MHz.
Weight (including speakers, monitor and software): 40lb.
Price: from 319.
Graphics: integrated graphics system with 3-D image video card.
Sound: options include high-quality stereo speakers for listening to music, DVDs, etc.
Software: a huge range of software available for download. Plays and burns CDs and DVDs.
Hardware: optional wide- or flat-screen monitor and standard keyboard.
Ease of use: comes with Windows Vista, latest version of Microsoft's operating system.