Year Released: 1981 (UK)

Original Price: £69.95 ready built (£49.95 in kit form)

Buy it now for: £10

Associated Magazines: Your Computer, MicroScope, Sinclair Programs

Why the ZX81 was great… It was cheap as chips; a physical checklist of fixed problems and subtle tweaks to the ZX80, with 30 quid shaved off the price. “Why not buy a ZX81?” was the motto of bedroom programmers everywhere. recommended gaming on the move.

It was only on the shelves for two years, but the ZX81 made a significant (if dichotomous) impact between 1981 and 1983, inaugurating a huge number of curious technophiles into the previously prohibitive world of home computing. Without this ostensibly minor upgrade to the ZX80, the extraordinarily prolific 8-bit revolution that quickly followed might well have known a significantly smaller congregation.

When discussing historical relevance it feels somehow trite to reduce matters to monetary concerns, but in the case of the ZX range of computers, the price tag genuinely was a momentous achievement for Sinclair Research. Home computing in the late-Seventies and early-Eighties presented a monumental financial investment that was entirely supported by a niche customer base. Computers weren’t the necessary, easily justifiable home appliance they are today, so anyone wanting to dabble in the new world of amateur code had to dig deep into threadbare pockets to satisfy their curiosity.

While other manufacturers vindicated their product’s astronomical costs with impressive, bullet-pointed lists of powerful processing capabilities, Uncle Clive aimed to astonish with a simple, lightweight price tag, and it was this distinctly British philosophy that put the ZX80 (the first machine to crack the £100 price barrier) into so many homes only a year before the ZX81.

All the astute pioneers in the computing and videogaming world during this embryonic phase knew the importance of affordability. Silicon was electronic gold, and if computer designers wanted to reduce costs they had to lighten the loads on their PCBs. At precisely the same time as Sinclair Research was pouring its talents into ridding excessive hardware, across the Atlantic Nolan Bushnell was offering huge incentives to Atari’s designers to reduce chip count in new games. It was exactly this line of minimalist thought that had prompted Steve Wozniak to reinvent Breakout and to create the Apple computer. It was no coincidence that those early campaigners made such a massive impact on the future of domestic computing and gaming: they all paid careful consideration to our wallets.

Steve Vickers, designer of the improved ZX81’s 8K ROM, vividly remembers just how important this business model was at Sinclair Research, and told us what it was like during those early days around Clive Sinclair’s offices.

“It was interesting to see the commercial pressures that drove the products. Launch dates were very important,” he begins. “The dates were those of particular exhibitions, and this meant that the deadlines were fixed externally. Hardware design was largely governed by using every possible, and often ingenious, means to reduce chip counts and production costs. Clive himself was exquisitely alert to these issues, and in a sense the nature of the actual product was secondary to him.”

This was the real, hidden strength of the ZX81 over its chip-heavy predecessor, and the reason it was an admittedly underpowered, yet highly accessible computing warhorse. While the ZX80 housed over 20 different ICs under its thin plastic skin, the ZX81’s brainpan was emptied of all but four vital chips; one of which was a custom IC compiling the majority of the ancillary functions into one slab of silicon. Of those four digital workhorses, the ROM was perhaps the only one which remained almost completely unaltered, though its development continued with a doubling of capacity up to a whopping 8K. As the man behind the re-engineering of the ZX81’s nervous system, Steve explains not only the advancements of the ROM, but its intricate similarities to its parent’s.

“John Grant’s 4K BASIC for the ZX80 was a miracle of compaction,” he says. “As far as possible I left its design and code intact and added the new ZX81 features to it in a modular way. I started by learning the Z80 assembler, which I’d never used before. The first task was adding a floating point maths package, which was big but fairly self-contained. I had to do some research into the Chebyshev polynomials I used for calculating functions, and devised a stack-based internal language to describe the algorithms. This was both compact and easy to program compared with raw assembler code. That was when I had to begin to understand the old system better in order to see how it needed modifying to integrate it with the old ZX80 system.”

While Steve might speak a language better understood by an EPROM burner, it’s easy to decipher that Sinclair Research had found precisely the right man to increase the capabilities of this new system. Indeed, Steve rather astutely approached the augmentation of the ZX franchise precisely as Clive intended to sell it – by way of upgrade and home industry.

3 GREAT ZX81 GAMES

3D Monster Maze



Pimania

Psion Flight Simulation



Read the full feature in Retro Gamer issue 45, on sale digitally from GreatDigitalMags.com

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