Happy 30th Birthday, Sinclair ZX Spectrum
The story of an historic micro
The Sinclair ZX Spectrum was launched 30 years ago today. At the Churchill Hotel, Clive - now Sir Clive - Sinclair stood before reporters and a barrage of camera flashbulbs to unveil the machine, the successor to the popular ZX81, on 23 April 1982.
Comparing the new machine to the BBC Micro Model A  - released the previous December - Sinclair said: "It's obvious at a glance that the design of the Spectrum is more elegant. What may not be so obvious is that it also provides more power."
Better looking than a BBC Micro? Sinclair's ZX Spectrum
Sinclair's previous microcomputer, the ZX81 , had been launched just over a year before, on 5 March 1981, and had proved a huge success. By December of that year, Sinclair Research had shifted a quarter of a million of the monochrome micros. But Commodore's Vic-20, which shipped in May 1981 after a late 1980 launch, had already heralded colour computing and it was clear to the Sinclair team that their next machine must be colour capable.
Trading colour for a low price was acceptable in 1981. It would not be so in 1982. Likewise, the new machine would need a proper, moving keyboard like those offered by almost all of its rivals, not another low-cost membrane keyboard like those of the ZX80 and ZX81.
But what to call this new, colour computer? During its development, the Spectrum was, for a time, called the ZX82, the logical successor to ZX80 and ZX81. But the stellar success of the ZX81 prompted Sinclair to consider alternatives.
The name that might have been: ZX81 Colour sample logotypes from 29 September 1981
Source: Rick Dickinson 
For a time, the new machine was the ZX81 Colour - aka the ZX81 C - and during September 1981, Sinclair's industrial designer, Rick Dickinson - flattering described by Sinclair User magazine at the time as a "blond, 26-year-old prodigy" - queued up a series of possible logotypes for a computer of that name. 'ZX81 Colour' also appeared on casing design sketches made by Dickinson during October 1981.
It's certainly the case that Clive Sinclair wanted to get the ZX81's follow-on out of the door very quickly, and to that end he wanted the new machine to involve as few internal changes as possible. That concept of the Spectrum as a 'ZX81-plus' may also have informed the early choice of name.
The 'Spectrum' moniker seems to have been a relatively late notion. The handle under which the new computer would be released was in play by February 1982 - it had been the ZX82 up until then - when Dickinson proposed a series of different logotypes and a variety of different approaches to the iconic colour slash across the keyboard.
Designer Rick Dickinson at Sinclair
The keyboard itself was still being revised through February 1982. Interestingly, some of Dickinson's sketches from the time show a roundel-on-square key design that, though absent from the first Spectrum, would appear on the Spectrum+ in October 1984.
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.
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.
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.
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."
The Spectrum's hardware engineer was Richard Altwasser. A Sinclair Research employee, he joined the company in September 1980. He devised the Spectrum's logic board, nominally working under the oversight of Sinclair's Chief Engineer, Jim Westwood . But with Westwood's attention centred on rescuing Sinclair's troubled flat-screen TV project, Altwasser appears to have had a surprisingly free hand - within the cost and schedule constraints imposed by the company.
"We had plenty of freedom working at Sinclair but at the end of the day the company was run by one man and if a decision needed to be made, there was one man [Clive Sinclair] who took that decision," Altwasser would say later in 1982.
Steve Vickers (top left) and Richard Altwasser (top right) in the 1980s. Steve Vickers (bottom left) now
Fortunately, Altwasser had a very good working relationship with Vickers which enabled the two to work closely, a fact that undoubtedly ensured Sinclair was able to release the Spectrum to all intents and purposes on schedule.
The two engineers' close partnership also led, in May 1982, to the pair leaving their respective employers to form a new home computer company, Rainbow Computing. Rainbow would soon be renamed Jupiter Cantab and go on to release the Jupiter Ace micro, a curious machine that looks like a cross between the ZX81 and the Spectrum and is most notable for eschewing the then de facto standard Basic programming language in favour of the lesser known Forth.
The Ace was a failure. Vickers subsequently became an academic, taking posts at Imperial College, London; the Open University; and, his current role, Senior Lecturer at the University of Birmingham .
Jupiter Cantab promotes the Jupiter Ace. But punters proved resistant to its charms
Source: Retrogeek 
Altwasser would return to Sinclair, surviving the company's acquisition by Amstrad in 1986 to become Amstrad's Engineering Director. He left in 1992. Since then he has held senior technical roles at a variety of companies, including RM, and is now "Head of Inspire" at interactive learning firm Promethean.
At the heart of Altwasser's Spectrum design was a Zilog Z80A processor clocked to 3.5MHz. Vickers' Basic would be burned into 16KB of Rom. Not that the full amount was required. At launch, 1.3KB was empty, originally earmarked for code that would support Sinclair's planned peripherals, most notably the Microdrive, which proved unavailable for testing during the firmware's development.
Inside the Spectrum, from the ZX Spectrum Introduction manual by Steve Vickers and Robin Bradbeer, bundled with the computer
Nor was it ready by April, but nothing could hold the launch back. So the Rom shipped incomplete. It was initially thought that early adopters would be offered a free Rom updates when the code was complete and new chips could be blown, but by June Sinclair had shipped so many first-generation machines - 75,000 in all, somewhat justifying Clive Sinclair's drive for a at-all-costs launch - that that plan was no longer financially viable.
Instead, the complete firmware would ship on the peripherals' adaptor units, taking over from the Rom chip in the Spectrum when necessary.
Making a clear leap forward from the ZX81's 1KB of memory, the Spectrum was offered with a choice of 16KB or 48KB Ram. The former, intended as the budget choice, was priced at £125; the 48KB Spectrum was £175. That was expensive in comparison with the sub-£100 ZX81, but impressively cheap when set alongside the £399 32KB BBC Micro Model B, launched the previous December.
Like the ZX81 before it and many other UK home computers, the Spectrum fed its video output through a radio frequency modulator to the aerial socket of and colour or monochrome TV. The computer's ten-octave, single-voice sound was pumped through an on-board speaker, quickly leading to a booming market in warranty voiding plug-in sound chips that relayed the audio out to the TV through the modulator signal.
The ZX Spectrum's colour choices
The Spectrum was initially capable of presenting a 32 x 24 grid of alphanumerical and block-graphic characters or a 256 × 192 pixel screen for graphics. Dots and characters could be black or any of seven colours - blue, red, purple, green, cyan, yellow and white - each set to one of two possible brightness values - giving 15 hues in all.
Altwasser's key achievement, for which he subsequently received a patent, was to store pixel colour information in a separate 32 x 24 array, leaving the 256 x 192 graphics store as a single bit per pixel array. The result was a highly compact graphics buffer, with the lot held in just 7KB of memory. The downside was that each 8 x 8 pixel block, which mapped onto an entry in the colour array - also known as the attribute array - could only contain two colours: one in the first four bits of the 8-bit byte, the other in the second four bits.
Let's play Hangman: a Sinclair Basic listing
The result: if a block contains a background image in, say, red and green, and, as a result of a yellow sprite graphic moving into that area, all the green pixels in the background suddenly turn yellow, a visual glitch called "attribute clash".
However, The Spectrum's keyboard was its arguably most divisive component, engendering either love or hate in potential buyers. Clive Sinclair had promised a fully moving keyboard, leading many observers and punters to hope for a typewriter-style keyboard. But that would have made the Spectrum much larger than it was, and that was not the Sinclair way.
Rick Dickinson's early sketches show that a more basic keyboard was always part of the plan. Curiously, an early, pre-release brochure I saw at the time has pale grey keys with a slightly glossy sheen - they looked like hard plastic keys of the kind found on calculators.
From smooth, shiny plastic to dead flesh? The Spectrum keyboard in Sinclair's pre-release brochure (top) and on shipping product (bottom)
When Spectrums began to land in users' hands, they keyboard would surprise many of them with its use of rubber keys uncharitably described at the time as offering the fell of "dead flesh". The hard plastic keys were merely part of a mock-up produced for designer Rick Dickson and used for promo work.
The Spectrum would finally gain a hard-key keyboard in 1984 with the release of the Spectrum+, a bid to win customers in a market already beginning to slow.
Before the arrival of the Plus and, a year later, the Spectrum 128, Altwasser's successors would go on to revamp his motherboard several times. Toward the end of 1982, Sinclair began shipping Spectrums with a second-gen logic board. The original board had 16KB of Ram soldered on - the 48KB machine's extra memory was mounted on a daughter card. The 'Issue 2' board had the extra 32KB soldered on too, reducing the cost.
Revamping the board
A glitch in some Issue 1 ULA (Uncommitted Logic Array) chips - basically a mass of logic gates to be used or ignored as the chip customers required - required the addition of a secondary integrated circuit to adjust the ULA's timing signal. That problem was repaired with the release of the Issue 2 motherboard.
Late in 1983, Sinclair introduced the Issue 3 motherboard, once more adjusting the chip layout, this time to reduce the machine's power consumption and eliminate the overheating problems that hit many Issue 1 and 2 Spectrums.
But these glitches failed to dent the Spectrum's popularity. Demand surged beyond Sinclair's planned 20,000-units-a-month output, leading to a backlog of 30,000 orders by July 1982, a month after the Spectrum began to ship, itself a month and a half after the machine's launch.
That month, the UK government included the 48KB Spectrum on a list of computers approved for secondary school use - the others were the BBC Model B and the Research Machines BBC-esque 480Z - with grants to enable them to buy the machines.
Through the Summer of 1982, thanks to a holiday at contract manufacturer Timex's Dundee plant, where the Spectrum was being assembled, the backlog grew to 40,000 units.
The Sinclair Microdrive and catridge: arrived too late - and didn't work so well when it did
Maybe education viewed the Spectrum as too entertainment-oriented, or perhaps the order backlog simply prevented schools getting hold of all the machines they would like. Either way, Sinclair never made much of a dent on the education market, eventually drumming up a tiny, two per cent share.
To calm ordinary punters' fevered brows, Clive Sinclair issued a public apology in September 1982 and gave waiting buyers the opportunity to get their money back. Those who took him up on the offer may well have gone for a ZX81, now selling for just under £50, as a stopgap.
By the time Sinclair had upped production, probably with the arrival of the less costly Issue 2 motherboard, some 60,000 Spectrums had shipped. A further 500,000 Issue 2 machines would ship through the remainder of 1982 and well into 1983, the vast majority of them sold direct by Sinclair itself, some 200,000 by the end of March 1983. Issue 3 added a further three million units to the overall total, though by now High Street shops like WH Smith, Boots, Currys and John Menzies were selling the Spectrum too.
QL-style Speccy: the Spectrum+
For the year to 31 March 1983, Sinclair announced sales totalling £54.53m, earning it £13.8m in profit.
In May 1983, Sinclair cut the price of the 16KB Spectrum to £99.95 and the 48KB model to £129.95. In July, Timex began selling an own-brand version of the Spectrum in the US, the TS-1500, licensed from Sinclair. In November, it released the Timex TS-2068, with a completely new case design. But sales proved poor and the company collapsed in 1984.
By mid-1984 the once seemingly unstoppable Spectrum was starting to run out of steam over here too. Sinclair had tried and spectacularly failed to enter the business computing market with the Motorola 68000-based QL, had commanded all of Sinclair's product development resources, leaving no room for work on a true Spectrum successor for the home market. So the Spectrum was tweaked again: a new, more rectangular, QL-style casing with hard plastic keys, creating the Spectrum+.
But with no other changes to the core Spectrum specification and a higher price - £179.95 - punters were not overwhelmed by the new Spectrum+ when it went on sale in October 1984. To make matters worse, Sinclair's quality control slipped (again) leading to high failure rates. If the Spectrum+ you bought worked, there was still a good chance one of more of the keys would come loose and fall off.
Hot sink ahoy! Sinclair's ZX Spectrum+ 128
Still, the Spectrum+ kept the brand alive through to February 1986 and the arrival of the Spectrum+ 128, which was, again, a regular Spectrum in a new case but this time with 128KB of Ram; MIDI output and three-channel sound courtesy of a new audio chip; an RS-232 port; and the ability to output to a monitor. And a big, very hot heat sink bolted onto the side.
Memory switching hardware ensured the Z80A CPU could flip between the two banks of 64KB making up the 128's memory map. It also had to handle switching between two 16KB banks of Rom, one for the original Spectrum Rom, the other for a new 128 Basic interpreter.
Sugar is the boss
By now, however, Sinclair was in trouble. A sudden, unexpected collapse in the home computer market in the run-up to Christmas 1984 hit the company hard, though its focus on low-cost machines ensured it didn't take the punishment meted out to many of its rivals, Acorn in particular. But the plunge ensured 1985 was a lean year, and Sinclair entered 1986 uncomfortably.
And was soon acquired by Amstrad, Alan Sugar's company, once known for its cheap but poor hi-fi and, at this point, for the well-received Amstrad CPC 64 home computer, which had gone on sale in June 1984, just as Sinclair was struggling to persuade buyers to upgrade to the QL.
Amstrad killed off the Spectrum 128 but maintained the Plus, understanding the benefit of a low-cost machine with a huge catalogue of games software behind it. Early in 1987, Amstrad released the Spectrum +2, a 128 with a new design featuring, as per the CPC series, a built-in cassette deck. It also removed the single-key Basic instruction entry system, a Sinclair trademark going back to the ZX80. Like the Plus, the Plus 2 was sold as a games machine - joysticks and a stack of games were bundled with the computer - pure and simple.
Having opted for a 3in, 350KB diskette system for its PCW-8256 word processor, launched in September 1985, and acquired a job lot of the non-standard storage media, Amstrad put a 3in diskette drive into a tweaked Spectrum +2 and released in it 1987 as the Spectrum +3. Like the PCW series, it could run the CP/M operating system out of the box, thanks to internal tweaks but the Plus 3 was again sold solely as a games machine.
Amstrad finally ended Spectrum production in 1990, though some sites put the date at 1988. Either way, the Plus 3 was the last home computer to carry the name. ®
The author would like to thank all those fellow enthusiasts for scanning and uploading so many adverts and manuals from the 1980s, without which this article would have been much less detailed.
Very special thanks also go to Rick Dickinson for his permission to use his sketches and design drawings.