The ZX Spectrum: Birthday memories

The ZX Spectrum: Birthday memories

Summary: It may have been startlingly modern once, but at 30, the Sinclair Spectrum is as close in time to the world's first commercial computers of the 50s as it is to the latest iPad.It's doing rather better than LEO, though; last year, around a hundred new programs were written for the Spectrum, there are double that number of emulators, and thousands of fans still chatter away online.

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TOPICS: Emerging Tech
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It may have been startlingly modern once, but at 30, the Sinclair Spectrum is as close in time to the world's first commercial computers of the 50s as it is to the latest iPad.

It's doing rather better than LEO, though; last year, around a hundred new programs were written for the Spectrum, there are double that number of emulators, and thousands of fans still chatter away online.

ZX Spectrum

The ZX Spectrum is 30 years old. It was nearly called 'the Rainbow'. Image credit: Gamespot

I was there. Not for the Spectrum itself (I was 16 when it was launched and should have been concentrating on my A-levels) but three years later, when I'd made my way to Sinclair Research to work on the Spectrum 128 ROMs — a job I kept after Sinclair went bust and I and the Speccy were purchased by Alan Sugar. That's another story: for now, to mark the original birth of the computer that most categorically changed my life (and my exam grades, ahem) here are five things I learned while working on the Spectrum that deserve a bit of an airing.

1. It nearly got called the Rainbow

Although there were various codenames for the ZX Spectrum and related projects such as ZX81 Colour, LC3 (Low Cost Colour Computer), ZX82 and so on, the move was towards something snappier and less technical.

Rainbow was high on the list (to the discomfort of those who could only think of Zippy and Bungle), but rather fortuitously DEC decided to call its (failed) PC line the DEC Rainbow and Spectrum was chosen instead. Given the connections between Sinclair and Cambridge, where Isaac Newton first explored the visible light spectrum, it seemed apposite. Better than Bungle, anyhow.

2. It never made any money for Sinclair

Although Sinclair's previous companies had made money — most notably with pocket calculators — Sinclair Research itself only had one real cash cow, the ZX81. It sold in the millions and made a very respectable profit.

The Spectrum, although a very strong seller, had a fatal flaw — it was desperately unreliable.

The Spectrum, although also a very strong seller and the linchpin of a much bigger programming and cultural scene than the ZX81 generated, had a fatal flaw — it was desperately unreliable.

The scuttlebut among the software developers in Sinclair was that up to 25 percent of them came out of the factory broken. Some of that was due to the manufacturer, Timex in Dundee (a city where so many ZX Spectrums were liberated from the factory in the early 80s they became a second currency), but most was due to over-ambitious expectations about how well cheap components would perform.

3. The source code was a mess

This I know, because my first job at Sinclair was to take the Spectrum ROM source code and make it work. Written by outside consultants and never subsequently touched in the years before the Spectrum 128 project was started, it lived in a small number of largely undocumented Z80 assembler files that were incompatible with Sinclair's development system. Even making it assemble and link to produce a bit-identical 16K ROM image to the one in the Spectrum itself was a challenge.

Fortunately, someone had done most of the work. Drs Ian Logan and Frank O'Hara had previously analysed the code and documented it in The Complete Spectrum ROM Disassembly, which was a far better reference for what was going on inside the Spectrum than anything Sinclair had.

Making the original stuff work, and adding enough documentation to it to make future developments easier, relied enormously on that book. I would say that the eight quid Sinclair spent on that book was the best investment the company ever made, were it not for the fact I'd paid for my own copy previously.

The original Spectrum source code was delivered to Amstrad — on 8-inch floppies, to make it more exciting for them — but there the trail runs cold. Enquiries with the company have failed to uncover the files. As of 2012, the Logan book is the only reference extant.

4. Sinclair didn't like the Spectrum

There are many reasons why Sinclair Research went to the wall, but one factor was that the company as a whole and Clive Sinclair in particular did not much like the Spectrum, even though attempts to move in a different direction through the QL business computer failed.

Sinclair Research, in Clive Sinclair's eyes, was a cutting-edge technology company doing serious, world-changing work. He even started a blue-sky division, the Metalab, to commercialise artificial intelligence, wafer-scale integration, advanced displays and so on.

The Spectrum, which was sold as a mainstream computer for education and home use, rapidly became a gaming platform. Sinclair did not want to be seen as a maker of gaming platforms, and so there was a lot less focus on developing that side of the company than trying to find ways to compete with IBM.

5. The Spectrum could bring a £60,000 computer to its knees

At Sinclair, a £60,000-plus DEC VAX 11/780 was used for software development, email and other shared activities — hardware design was done mostly on Valid workstations (one of which was broken so often it acquired an 'In' before its badge).

Pretty much standard corporate computing for the time, the '780 was a powerful beast capable of supporting forty-odd terminals over miles of serial cables. As the Sinclair lab was on top of the only hill for miles, lightning strikes on a radio mast nearby were common had a habit of frying all the line driver cards in the computer. Amazingly, this was never given as an excuse for delivery delays.

All the Spectrum software development tools ran under CP/M, the standard micro-computer operating system before MS-DOS took over. CP/M was designed to run on the 8080 and Z80 microprocessors, and a card with two Z80s lived in the VAX to run the operating system and interface it to the users. If two people were using the card then you could opt to run a Z80 emulator on the VAX proper — which absolutely soaked up all the processing power it had, slowing things down to an unusable crawl for everyone else.

The result was that if you had to re-assemble and link the Spectrum source code under those conditions, the lack of a £6 Z80 processor knocked out a £60,000 VAX — and made a chap vastly unpopular with his co-workers. Though not as unpopular as remapping their VT-220 terminal keyboards to Danish.

Topic: Emerging Tech

Rupert Goodwins

About Rupert Goodwins

Rupert started off as a nerdy lad expecting to be an electronics engineer, but having tried it for a while discovered that journalism was more fun. He ended up on PC Magazine in the early '90s, before that evolved into ZDNet UK - and Rupert evolved with them into an online journalist.

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6 comments
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  • The Spectrum certainly had a reputation for unreliability, but I think some of that was down to poor version control: Sinclair sneakily made some tweaks to the ROM (I think - but where else?) that made later Spectrums incompatible with earlier models. I certainly remember that my "Atic Atac" game would make my Spectrum reboot almost immediately. Mind you, once the Spectrum had gained a bad reputation then shops would simply replace them without question - which can't have helped Sinclair's profitability.
    Zogg
  • Thank you for a great article. The best I've read today in fact.

    Would love to read your experiences of the Amstrad take-over sometime. I've read some interesting things about when they first saw the Speccy circuit diagrams at Amstrad and wondered how it could possibly function, but it would be great to hear more! It's not a terribly well documented part of our computing history.
    anonymous
  • I bought one of those ZX Spectrum years ago, it was my 1st computer, not that you could do a lot with it, but I still have it along with a plug in memory
    anonymous
  • There were never any changes to the ROM, too many had been shipped to make it worthwhile calling them back in and replacing them. The incompatibilites you experienced were due to the keyboard scanning hardware in the ULA being tightened up to more closely match the specification, and lazy programmers who didn't mask out the data that wasn't connected to anything and so could legitimately be any random value.
    There were slight changes to the 48K ROM when it was used in the Spectrum 128, as detailed by Rupert above, but that was the Spectrum 128, not the Spectrum.
    anonymous
  • > There were never any changes to the ROM, too many had been shipped to
    > make it worthwhile calling them back in and replacing them.

    Sorry, I'm not convinced: my recollection is that Sinclair silently tweaked later Spectrums and never had any intention of recalling earlier models for replacement.
    Zogg
  • Good work Rupert! It took me ages to realise the Z80 had an [undocumented] 50Hz keyboard scan interrupt, which interfered with a digital sound sampler I designed at the time for Datel Electronics. A DI fixed it. I have great fun with the Spectrum designing a hardware interface for the bus.
    anonymous