ZX Spectrum

Ah, the ZX Spectrum. A relic from an era when computers were less about sleek aesthetics and more about raw, unadulterated potential, crammed into unassuming boxes. You want to know about it? Fine. Just don't expect me to wax poetic.

ZX Spectrum

The ZX Spectrum, a name that still echoes with a peculiar nostalgia, is an 8-bit home computer that emerged from the fertile, albeit slightly eccentric, mind of Sinclair Research. It wasn't just a machine; it was a catalyst, a pivotal player in the burgeoning history of personal computing and, more importantly, in the grand theatre of video games. Especially in the United Kingdom, where it became more than just a piece of technology – it was a cultural phenomenon. With over five million units sold, it etched its name into the annals of British computing history. Its UK debut was on 23 April 1982, with the United States catching up in November 1983 and Europe following suit in 1984.

The brainchild of the rather singular English entrepreneur and inventor Sir Clive Sinclair, and meticulously crafted by his small, dedicated team in Cambridge, the Spectrum was manufactured in Dundee, Scotland, by the venerable Timex Corporation. The design philosophy was brutally simple: small, uncomplicated, and, above all, affordable. Fewer components meant lower costs, a shrewd move in a market still finding its feet. The "Spectrum" moniker wasn't arbitrary; it was a deliberate nod to its colour display, a stark contrast to the monochromatic austerity of its predecessor, the ZX81. Rick Dickinson, a designer with a knack for the iconic, sculpted its distinctive case, complete with that now-legendary rainbow motif and that rather unique rubber keyboard. Forget dedicated monitors; the Spectrum piped its output directly to your television via an RF modulator. And how did you load your digital treasures? Onto compact audio cassettes, of course.

Initially, the Spectrum was available through mail order, a system that quickly buckled under its own success, leading to considerable backlogs. Eventually, it found its way onto the shelves of High Street chains across the UK. Across the pond, it was rebranded as the Timex Sinclair 2068 in 1983, with a European iteration known as the Timex Computer 2048. There were, in total, seven distinct models, from the humble 16 KB RAM starter to the more ambitious ZX Spectrum +3, boasting 128 KB RAM and a built-in floppy disk drive by 1987. Its primary rivals in the fierce home computer arena were the Commodore 64, the BBC Micro, the Dragon 32, and the diverse Amstrad CPC range. The sheer volume of software produced for the Spectrum is staggering – over 24,000 distinct titles.

The arrival of the Spectrum didn't just sell computers; it ignited an explosion of software and hardware development, the ripples of which are still felt today. It was one of the first home computers to truly target the mainstream UK audience, and many credit it with single-handedly igniting the British information technology industry. For a considerable period, it reigned supreme as Britain's top-selling computer, a title it held until the Amstrad PCW eventually nudged it aside in the 1990s. Its production run finally ceased in 1992, marking the end of an era.

History

Sir Clive Sinclair, a figure whose name became synonymous with innovation and, at times, a certain audacious optimism, was the driving force behind Sinclair Research. His journey into the world of electronics began long before the Spectrum. In 1961, fresh out of A-levels, he founded Sinclair Radionics, a venture dedicated to bringing his inventive ideas to life. By 1972, Sinclair was already making waves, locking horns with Texas Instruments in the race to produce the world's first pocket calculator, the Sinclair Executive. The mid-1970s saw Sinclair Radionics churning out a diverse range of products, from handheld calculators to miniature televisions, and the notoriously ill-fated Black Watch wristwatch. Financial woes, however, forced Sinclair to seek investment from the National Enterprise Board (NEB), who acquired a significant stake and streamlined the company's focus. The relationship with the NEB proved strained, and by 1979, they opted to dissolve Sinclair Radionics, selling off its television division to Binatone and its calculator operations to ESL Bristol.

The fallout from this restructuring left Sinclair with a substantial investment loss but also a considerable severance package. He then enlisted the help of a former associate, Christopher Curry, to establish a new venture, Science of Cambridge Ltd., in July 1977, so named for its proximity to the esteemed University of Cambridge. The advent of affordable microprocessors at this time sparked Sinclair's interest in computer kits, leading to the production of the MK14, a computer teaching kit that proved to be a modest success due to its low price point. Buoyed by this, Sinclair rebranded his company to Sinclair Research and set his sights on the personal computer market. The mantra of affordability remained paramount, a critical lesson learned from previous ventures where products were outpriced by their American and Japanese counterparts.

On 29 January 1980, the ZX80 home computer was unveiled, achieving immediate popularity. It was a groundbreaking machine, notable for being one of the first computers available in the United Kingdom for under £100. In a testament to Sinclair's unconventional approach, no market research was conducted prior to the ZX80's launch; Sinclair famously claimed he "simply had a hunch" about public interest and proceeded to order a massive 100,000 sets of parts to facilitate high-volume production.

The ZX81, launched on 5 March 1981, propelled the company to even greater heights, selling over 1.5 million units globally, with a significant 60% of those sales occurring outside Britain. As Ben Rosen observed, the ZX81's incredibly low price point had effectively "opened up a completely new market among people who had never previously considered owning a computer." Computing in Britain, once the domain of professionals and dedicated hobbyists, was suddenly accessible to the general public. The ZX81's commercial triumph cemented Sinclair Research's position as a leading British computer manufacturer, with Sinclair himself reportedly finding the machine's reception both "amusing and gratifying."

Development

The genesis of the ZX Spectrum project dates back to September 1981, a mere few months after the ZX81's triumphant release. Sir Clive, ever the pragmatist, aimed to render his own products obsolete before competitors could. To expedite development and control costs, elements of the ZX80 and ZX81 designs were repurposed. The development team, a compact group of around 20 engineers, was housed in a modest office at 6 King's Parade in Cambridge. During its nascent stages, the machine was internally referred to as the ZX81 Colour or ZX82, a clear indication of its primary advancement: colour graphics, a significant departure from its monochrome predecessors. The "Spectrum" designation arrived later, specifically chosen to underscore its expanded 15-colour palette. Beyond the addition of a new crystal oscillator and extra chips to augment its memory capacity by several kilobytes, the ZX Spectrum was, in essence, envisioned as a "ZX81 with colour," as articulated by Sinclair's marketing manager. Furthermore, the team sought to consolidate the ZX81's separate audio and video memory sections into a unified bank.

The intricate hardware design of the ZX Spectrum was the responsibility of chief engineer Richard Altwasser. His most significant contribution was the development of the semi-custom uncommitted logic array (ULA) integrated circuit, a single chip that ingeniously integrated the core hardware functionalities. Altwasser devised a graphics mode that demanded minimal memory, less than 7 kilobytes, and implemented it within the ULA. The bulk of the ROM code was penned by Steve Vickers. Extensive deliberations between Altwasser and the Sinclair engineering team culminated in a consensus that the ZX Spectrum required high-resolution graphics, a minimum of 16 kilobytes of memory, an enhanced cassette interface, and an impressive colour palette. Achieving these ambitious goals necessitated a critical architectural decision: decoupling the central processing unit (CPU) from the display generation process to maximize its operational efficiency, a departure from the ZX81's integrated approach.

The introduction of colour proved to be a substantial hurdle for the engineers. A Teletext-like system, where colour-change codes were embedded within text lines, was briefly considered but ultimately deemed unsuitable for the demands of high-resolution graphics and complex diagrams requiring frequent colour transitions. Altwasser's ingenious solution was to assign a colour attribute to each character position on the screen. This strategy consumed eight bits of memory per character cell: three bits for the foreground colour, three for the background colour, one for brightness enhancement, and one for the flashing effect. This comprehensive scheme occupied just under 7 kilobytes of memory, leaving a substantial 9 kilobytes available for program development, a figure that met with considerable satisfaction from the team.

A significant portion of the firmware was developed by computer scientist Steve Vickers of Nine Tiles. He was instrumental in compiling the control routines, ultimately producing the Sinclair BASIC interpreter, a bespoke version of the widely used BASIC programming language. The creation of a custom interpreter was crucial for fitting its extensive functionality within the severely limited space of the read-only memory (ROM). The development process was not without its friction; disagreements arose between Nine Tiles and Sinclair Research. Sinclair Research prioritized an expedited product launch, largely by minimizing changes to the software inherited from the ZX81, which itself was an evolution of the ZX80's software. However, the ZX80's software architecture was fundamentally designed for a highly constrained memory environment and, in the opinion of Nine Tiles, was ill-suited for the increased processing demands of the ZX Spectrum. Sinclair favoured augmenting the existing framework with expansion modules, a strategy that Nine Tiles opposed. Ultimately, both design paths were pursued, but Vickers and Nine Tiles were unable to finalize their version before the Spectrum's release, and it was not implemented.

The distinctive case and vibrant design of the ZX Spectrum were the work of Rick Dickinson, a young British industrial designer previously tasked with the ZX81's design. Dickinson was challenged to create a more streamlined and "marketable" aesthetic for the new machine, while simultaneously ensuring that all 192 BASIC functions could be accommodated on the 40 physical keys. Early design sketches from August 1981 depicted a more angular, wedge-shaped case, reminiscent of an updated ZX81. Dickinson eventually settled on a flatter design, featuring a raised rear section and rounded sides, intended to convey a sense of advanced technology rather than a mere incremental upgrade. In his pursuit of appropriate branding, Dickinson proposed several logo designs, all incorporating the now-iconic rainbow stripes across the keyboard.

The design of the Spectrum's rubber keyboard represented a significant simplification, reducing hundreds of components to a mere "four to five" moving parts through the application of novel technology. The keyboard design was still in flux as late as February 1982; some sketches reveal a roundel-on-square key arrangement that would later appear on the Spectrum+ model. Dickinson, reflecting in 2007, emphasized that "everything was cost driven," and that the Spectrum's minimalist, Bauhaus-inspired approach resulted in an elegant, if not entirely revolutionary, form. The very drawing board Dickinson used for the ZX Spectrum's design is now a treasured exhibit at the Science Museum in London.

The necessity for an improved cassette interface was acutely felt by ZX81 users who frequently encountered difficulties saving and loading programs. To achieve higher data transfer speeds, the team reduced the duration of the tones used to represent binary data. While the initial target was 1000 baud, they successfully surpassed this, reaching a considerably faster 1500 baud. To enhance reliability, a leading period of constant tone was incorporated, allowing the cassette recorder's automatic gain control to stabilize, thereby minimizing tape hiss. A Schmitt trigger was integrated into the ULA to filter out noise from the received signal. A key advantage over the ZX81 was the Spectrum's ability to maintain its display during data transfer, enabling programs to present a splash screen while loading.

As with the ZX81, the ZX Spectrum was manufactured in Dundee, Scotland, by Timex Corporation at their Dryburgh factory. Prior to their involvement with Sinclair, Timex was primarily known for mechanical watch production and had limited experience in electronics assembly. Fred Olsen, a director at Timex, recognized the potential for diversification and secured a contract with Sinclair.

Launch

The ZX Spectrum was officially unveiled to the press by Sir Clive Sinclair at the Churchill Hotel in Marylebone, London, on 23 April 1982. Later that same week, the machine was the subject of considerable fanfare at the Earl's Court Computer Show in London and the ZX Microfair in Manchester. The launch comprised two models: a 16KB 'basic' version and a more capable 48KB variant. The 16KB model was priced competitively at £125, significantly undercutting its main rival, the BBC Micro. The 48KB version, at £175, was roughly a third of the cost of an Apple II computer. Upon release, the keyboard's rubber keys, described as having the feel of "dead flesh," surprised many users. Sir Clive himself acknowledged the keyboard's "unusual" nature, but this did little to deter consumer enthusiasm.

Ninety-year-old Harold Macmillan utilizing a ZX Spectrum, with Sir Clive Sinclair observing (1984).

Despite overwhelming demand, Sinclair Research was notoriously slow in delivering the ZX Spectrum. Their strategy of accepting mail-order sales before units were readily available ensured a steady cash flow but resulted in a severely limited distribution. Nigel Searle, the recently appointed head of Sinclair's computer division, stated in June 1982 that there were no immediate plans to stock the machine in WHSmith, Sinclair's primary high-street retailer at the time. Searle reasoned that the mail-order system was in place due to a lack of "obvious" retail outlets in the UK capable of selling personal computers, and that continuing with mail-order was more financially sound. This cautious distribution approach drew criticism, leading to a deluge of letters and calls from frustrated customers. Demand far outstripped Sinclair's projected production capacity of 20,000 units per month, resulting in a backlog of 30,000 orders by July 1982. This backlog swelled to 40,000 units due to a scheduled holiday shutdown at the Timex factory that summer. Sinclair issued a public apology in September of that year, promising to clear the backlog by the month's end. Supply only began to normalize around the 1982 Christmas season.

Production was significantly boosted by the introduction of the less expensive Issue 2 motherboard, a revised main circuit board that addressed manufacturing defects that had plagued the initial model. Sales of the ZX Spectrum reached an impressive 200,000 units within its first nine months and climbed to 300,000 for the entire first year. By August 1983, total sales across Britain and Europe had surpassed 500,000 units, with the millionth Spectrum rolling off the production line on 9 December 1983. By this stage, an average of 50,000 units were being sold each month.

In July 1983, an enhanced version of the ZX Spectrum was launched in the United States under the name Timex Sinclair 2068. Advertisements boasted of its 72 kilobytes of memory and full colour and sound capabilities for under $200. Despite these advancements over its British counterpart, sales were disappointing, and Timex Sinclair declared bankruptcy the following year.

Success and Market Domination

A cornerstone of Sinclair Research's marketing strategy involved consistent price reductions at opportune moments to maintain its dominant market share. Ian Adamson and Richard Kennedy noted that Sinclair's approach was designed to "panic" the competition and secure their leading position. While most companies typically lowered prices when sales began to falter, Sinclair Research discounted their products shortly after sales peaks, throwing competitors into "utter disarray." Sinclair Research reported a profit of £14 million in 1983, a substantial increase from £8.5 million the previous year. Turnover more than doubled, from £27.2 million to £54.5 million, equating to roughly £1 million for every employee directly employed by the company.

Sir Clive Sinclair himself became the public face of the ZX Spectrum's marketing campaign, imbuing the business with a personal touch. Sinclair Research was consistently portrayed in the media as a plucky British underdog challenging the technological and marketing might of massive American and Japanese corporations. As David O'Reilly observed in 1986, Sinclair had leveraged astute public relations, particularly by cultivating his image as a Briton taking on the world, to become "the best-known name in micros." The press embraced Sinclair's persona, with The Sun even hailing him as "the most prodigious inventor since Leonardo da Vinci." Adamson and Kennedy further elaborated that Sinclair transcended the role of a mere microcomputer manufacturer, "accepted the mantle of pioneering boffin leading Britain into a technological utopia." His significant contributions to the technology sector were recognized when he was knighted in the Queen's 1983 Birthday Honours List, a recommendation made by Margaret Thatcher.

The United Kingdom remained remarkably insulated from the effects of the devastating video game crash of 1983, largely due to the widespread adoption of home computers like the ZX Spectrum. The microcomputer market continued its expansion, and game development thrived, unhindered by the turbulence affecting American markets. Computer games maintained their dominance in the British home video game market until they were eventually surpassed by consoles from Sega and Nintendo in 1991. By the close of 1983, over 450 companies in Britain were engaged in selling video games on cassette, a significant increase from just 95 the year prior. An estimated 10,000 to 50,000 individuals, predominantly young men, were developing games from their homes, often driven by advertisements in popular magazines. This period of rapid growth in video games has been likened to the punk subculture, characterized by young people monetizing their creative endeavors.

By the mid-1980s, Sinclair Research commanded an impressive 40 percent share of the British home computer market. Sales during the 1984 Christmas season were described as "extremely good." In early 1985, the British press began to report that the home computer boom was over, prompting many companies to slash hardware prices in anticipation of declining sales. Despite this market shift, Sinclair's success was still being celebrated; at the Which Computer? show in Birmingham, the five-millionth Sinclair machine, a gold-finished QL, was awarded as a prize.

Later Years and Company Decline

The ZX Spectrum's successor, the Sinclair QL, was officially announced on 12 January 1984, shortly before the Macintosh 128K entered the market. In contrast to its predecessors, the QL was targeted towards more discerning, professional home users. However, fully functional QLs did not become available until late summer, and Sinclair faced upheld complaints from the Advertising Standards Authority (ASA) in May of that year regarding delays, particularly allegations of cashing cheques months before machines were shipped. By the autumn of 1984, Sinclair was still publicly predicting that the QL would be a "million seller," with 250,000 units expected to be sold by the year's end. QL production was halted in February 1985, and its price was halved by the end of the year. It ultimately proved to be a commercial disappointment, with only 139,454 units manufactured.

The ZX Spectrum+, a rebranded ZX Spectrum with identical technical specifications but a QL-inspired keyboard, was introduced in October 1984 and became available in WHSmith's stores the following day. Retailers stocked the device in large quantities, anticipating strong Christmas sales. However, its performance fell short of projections, leading to a significant decline in Sinclair's order revenue in January as retailers were left with substantial unsold inventory. An upgraded model, the ZX Spectrum 128, was released in Spain in September 1985, financed by the Spanish distributor Investrónica. The UK launch was delayed until January 1986 to clear the considerable backlog of the previous model.

While the Sinclair QL was in development, Sinclair also harbored ambitions of replicating his Spectrum success in the nascent electric vehicle market, which he believed was ripe for innovation. On 10 January 1985, Sinclair unveiled the Sinclair C5, a single-person battery electric recumbent tricycle. This marked the culmination of Sir Clive's long-standing fascination with electric vehicles. The C5 proved to be a significant commercial failure, selling only 17,000 units and resulting in a £7 million loss for Sinclair. It has since been widely regarded as "one of the great marketing bombs of postwar British industry." The ASA mandated that Sinclair withdraw advertisements for the C5 after determining that the company's claims regarding its safety were unsubstantiated.

The combined failures of the C5 and the QL eroded investor confidence in Sinclair's judgment. In May 1985, Sinclair Research announced plans to raise an additional £10 to £15 million for organizational restructuring, but securing these funds proved challenging. In June 1985, business magnate Robert Maxwell revealed a takeover bid for Sinclair Research through Hollis Brothers, a subsidiary of his Pergamon Press. However, this deal was terminated in August 1985. On 7 April 1986, the company sold its entire computer product line, along with the "Sinclair" brand name, to Alan Sugar's Amstrad for £5 million. This acquisition sent ripples through the London Stock Exchange, though Amstrad's shares soon stabilized, with one broker commenting that "the City appears to have taken the news in its stride." Amstrad's takeover led to the release of three improved ZX Spectrum models throughout the late 1980s.

By 1990, Sinclair Research had dwindled to just Sinclair and two other employees, a stark contrast to its peak of 130 employees in 1985. The ZX Spectrum was officially discontinued in 1992, after a decade on the market.

Hardware

The ZX Spectrum's colour palette was one of its defining features.

At its heart was a Zilog Z80 microprocessor, an 8-bit powerhouse operating at a clock speed of 3.5 MHz. The original ZX Spectrum models came equipped with 16 KB of ROM and either 16 KB or 48 KB of RAM.

Graphics

The video output utilized an RF modulator, designed to connect to standard television sets of the era. Text was displayed in a grid of 32 columns by 24 rows, using characters from the ZX Spectrum character set or custom alternatives. The machine offered a palette of 15 distinct colours: seven saturated colours, each available in two brightness levels, plus black. The image resolution was 256 × 192 pixels, though subject to the same colour limitations. Colour information was stored separately from the pixel bitmap in a 32 × 24 grid, corresponding to the character cells. This architecture meant that all pixels within an 8 × 8 character block shared a single foreground and background colour. This ingenious design was patented by Altwasser.

An "attribute" comprised a foreground and background colour, a brightness setting (normal or bright), and a flashing flag that caused the two colours to alternate. This system resulted in what became known as attribute clash, where the desired colour for a specific pixel could not always be selected, being constrained by the colour attributes of the entire 8 × 8 block. This limitation became a defining characteristic of the Spectrum, compelling game developers to devise creative workarounds. Competitors like the Amstrad CPC and Commodore 64 did not suffer from this issue. While the C64 also used colour attributes, it offered a special multicolour mode and hardware sprites that bypassed attribute clash.

The effect of attribute clash on an MSX computer, illustrating a similar graphical challenge.

Sound

Sound reproduction was handled by a single-channel beeper, capable of generating ten octaves. Sound was produced by rapidly toggling a single bit on and off. From within BASIC, the BEEP command allowed for the playback of sounds with specified pitch and duration. Crucially, the processor was fully occupied with the BEEP command until the sound concluded, limiting concurrent operations. Despite these constraints, it represented a significant improvement over the complete silence of the ZX81. Programmers ingeniously devised workarounds, exploring unconventional methods such as programming the beeper to emit multiple pitches simultaneously.

Later software introduced support for two-channel sound playback. The machine featured an expansion bus edge connector and 3.5 mm audio in/out ports for connecting a cassette recorder to load and save programs and data. The • EAR port offered a higher output than the • MIC port and was recommended for headphones, while the • MIC port was intended for connection to external audio devices as a line-level input source.

Firmware

The machine's Sinclair BASIC interpreter resided within a 16 KiB ROM, alongside essential system routines. The ROM code, responsible for tasks such as floating point calculations and expression parsing, bore striking resemblances to that of the ZX81, although some outdated routines persisted in the Spectrum ROM. The Spectrum's keyboard was uniquely imprinted with BASIC keywords. Many keywords could be entered with a single keystroke, while others required mode changes via a few keystrokes.

The BASIC interpreter was derived from the one used on the ZX81. BASIC programs written for the ZX81 could be transferred to the ZX Spectrum with minimal modification. However, Spectrum BASIC introduced numerous enhancements, significantly improving its usability. The ZX Spectrum character set was expanded compared to the ZX81, which notably lacked lowercase letters. Spectrum BASIC incorporated additional keywords to facilitate better graphics and sound capabilities, and support for multi-statement lines was introduced. The built-in ROM tape modulation routines for cassette data storage enabled data transfers at an average speed of 171 bytes per second, with a theoretical peak speed of 256 bytes/s. This tape modulation was considerably more advanced than the ZX81's, achieving approximately four times the average speed.

Sinclair Research Models

ZX Spectrum

The original ZX Spectrum is fondly remembered for its distinctive rubber chiclet keyboard, its compact size, and the iconic rainbow motif. It was first released on 23 April 1982, with a 16 KB RAM version priced at £125 (equivalent to £557 in 2023) and a 48 KB version at £175 (equivalent to £780 in 2023). These prices were subsequently reduced in 1983 to £99 (equivalent to £422 in 2023) and £129 (equivalent to £550 in 2023) respectively. Owners of the 16 KB model could opt for an internal 32 KB RAM upgrade. For early "Issue 1" machines, this involved a daughterboard. Later revisions required the installation of eight dynamic RAM chips and a few TTL chips. Users could also send their 16K Spectrums to Sinclair for professional upgrading to 48 KB versions. Later revisions contained 64 KB of memory, though only 48 KB was directly accessible. External 32 KB RAM packs that slotted into the rear expansion port were also available from third-party manufacturers. Both original machines featured 16 KB of onboard ROM.

Distinguishing between "Issue 1" ZX Spectrums and later Issue 2 or 3 models is possible by observing the keycap colour: light grey for Issue 1, and a blue-grey for subsequent machines. Although the official service manual indicated the manufacture of approximately 26,000 original boards, subsequent serial number analysis suggests that only 16,000 were produced, with most falling within the serial number range of 001-000001 to 001-016000. An online tool now exists to help users determine the likely issue number of their ZX Spectrum by inputting its serial number.

These models underwent numerous motherboard design revisions throughout their production life, primarily to enhance manufacturing efficiency but also to rectify bugs found in earlier boards. Another notable issue concerned the Spectrum's power supply. In March 1983, Sinclair issued an urgent recall notice for all models purchased after 1 January 1983. Plugs with a non-textured surface posed a shock hazard and owners were instructed to return them to a warehouse in Cambridgeshire for a replacement within 48 hours.

ZX Spectrum+

The ZX Spectrum+, released on 15 October 1984, was priced at £179. It was assembled by AB Electronics in South Wales and by Samsung in South Korea. This 48 KB Spectrum introduced a new QL-style case featuring an injection-moulded keyboard and a reset button. Electronically, it was identical to the preceding 48 KB model. The Spectrum+ outsold its rubber-key predecessor by a two-to-one margin. However, some retailers reported a failure rate of up to 30%, a notable increase compared to the older model's typical 5–6%. In early 1985, the original Spectrum was officially discontinued, and the ZX Spectrum+ saw its price reduced to £129.

ZX Spectrum 128

In 1985, Sinclair collaborated with their Spanish distributor, Investrónica (a subsidiary of the El Corte Inglés department store group), to develop the ZX Spectrum 128, codenamed "Derby." Investrónica had previously assisted in adapting the ZX Spectrum+ for the Spanish market following the introduction of a special tax on computers with 64 KB RAM or less, and a law requiring all computers sold in Spain to support the Spanish alphabet and display messages in Spanish.

The ZX Spectrum 128 shared a similar appearance with the ZX Spectrum+, with the notable addition of a large external heatsink for the internal 7805 voltage regulator on the right side of the case, replacing the internal heatsink of earlier versions. This prominent external heatsink earned the system the nickname "The Toast Rack". New features included 128 KB RAM with RAM disc commands, three-channel audio via the AY-3-8912 chip, MIDI compatibility, an RS-232 serial port, an RGB monitor port, 32 KB of ROM featuring an improved BASIC editor, and an external keypad.

The machine was unveiled and launched simultaneously in September 1985 at the SIMO '85 trade show in Spain, priced at 44,250 pesetas. Sir Clive later presented the ZX Spectrum 128 at London's The May Fair Hotel, acknowledging that entertainment was the primary use of home computers. Due to the substantial inventory of unsold Spectrum+ models, Sinclair opted not to launch the 128 in the United Kingdom until January 1986, at a price of £179.

The Zilog Z80 processor used in the Spectrum possesses a 16-bit address bus, limiting direct memory addressing to 64 KB. To accommodate the additional 80 KB of RAM, designers employed bank switching to make the new memory accessible in eight 16 KB pages at the top of the address space. The same technique was used to switch between the new 16 KB editor ROM and the original 16 KB BASIC ROM at the bottom of the address space.

The new sound chip and MIDI output capabilities were exposed to the BASIC programming language through the PLAY command. A new command, SPECTRUM, was introduced to switch the machine into 48K mode while preserving the current BASIC program. However, there was no command to revert to 128K mode. To allow BASIC programmers to access the extra memory, a RAM disk was implemented, enabling file storage within the additional 80 KB of RAM. The new commands replaced two existing user-defined character slots, leading to compatibility issues with certain BASIC programs. Unlike its predecessors, the ZX Spectrum 128 lacked an internal speaker, relying solely on the television's speaker for sound output.

Amstrad Models

ZX Spectrum +2

The ZX Spectrum +2 marked Amstrad's entry into the Spectrum market following their acquisition of the Spectrum range and the "Sinclair" brand in 1986. It featured a grey case, a spring-loaded keyboard, dual joystick ports, and an integrated cassette recorder dubbed the "Datacorder" (similar to the Amstrad CPC 464). The boot-up message proudly declared "© 1986 Amstrad." Technically, it was largely identical to the ZX Spectrum 128 and retailed for £149.

The new keyboard lacked the BASIC keyword markings found on earlier Spectrums, with the exception of LOAD, CODE, and RUN. Instead, the +2 offered a menu system, closely resembling that of the ZX Spectrum 128, allowing users to switch between 48K BASIC programming (with keywords) and 128K BASIC programming, where all words, both keywords and standard commands, had to be typed out in full. Despite these changes, the keyboard layout remained the same as the 128.

ZX Spectrum +3

Launched in 1987, the ZX Spectrum +3 replaced the cassette drive with a built-in 3-inch floppy disk drive. Initially priced at £249, it was later retailed for £199. It was the only Spectrum model capable of running the CP/M operating system without requiring additional hardware. Unlike its predecessors, the ZX Spectrum +3 utilized a DIN connector for its power supply.

Significant hardware alterations resulted in a series of incompatibilities. The removal of several lines on the expansion bus edge connector caused issues with some peripherals. Furthermore, changes in memory timing led to certain RAM banks becoming contended, impacting high-speed colour-changing effects. The keypad scanning routines from the ROM were also omitted, rendering some older 48K and 128K games inoperable. The ZX Interface 1 also proved incompatible due to discrepancies in ROM and expansion connectors, preventing the use of Microdrive units.

Production of the +3 ceased in December 1990, reportedly in response to Amstrad's relaunch of their CPC range. At the time of discontinuation, approximately 15% of all ZX Spectrums sold were +3 models. The +2B model, the only other model still in production, continued to be manufactured, as it was not considered to be in direct competition with other Amstrad computer offerings.

ZX Spectrum +2A, +2B and +3B

The ZX Spectrum +2A was a revised version of the Spectrum +2, utilizing the same circuit board as the Spectrum +3. It was released in late 1988 and, unlike the original grey +2, featured a black casing. The Spectrum +2A/+3 motherboard (AMSTRAD part number Z70830) was designed to accommodate either a +2-style "datacorder" or a floppy disk controller. The power supply for the ZX Spectrum +2A shared the same pinout as the +3.

The ZX Spectrum +2B and ZX Spectrum +3B were released in 1989. They were functionally similar to the Spectrum +2A and +3, respectively, though modifications were made to the audio output signal generation to address clipping issues. The +2B board lacked provisions for floppy disk controller circuitry, while the +3B motherboard did not include connections for an internal tape drive. Production of all Amstrad Spectrum models concluded in 1992.

Licences and Clones

Official Licences

The Timex Sinclair 2068, released in 1983 for the American market.

Sinclair Research granted a licence for the ZX Spectrum design to the Timex Corporation in the United States. Timex marketed several computer models under the Timex Sinclair brand, including an enhanced variant of the original Spectrum known as the Timex Sinclair 2068. This upgraded model offered improvements in sound, graphics, and other areas, though Timex's versions were generally not compatible with Sinclair systems.

The Timex Computer 2048, highly compatible with the ZX Spectrum 48K, achieved considerable success in both Portugal and Poland.

Timex of Portugal developed and produced several branded computers, including a PAL region-compatible version of the Timex Sinclair 2068, known as the Timex Computer 2048. This variant featured distinct buffers for both the ULA and the CPU, significantly enhancing compatibility with ZX Spectrum software compared to its American counterpart. Software developed for the Portuguese-made 2048 remained fully compatible with its American sibling, as the ROMs were identical. Timex of Portugal also created a ZX Spectrum "emulator" in cartridge form. Further enhancements were introduced, including a BASIC64 cartridge that enabled the use of high-resolution (512x192) modes. This model enjoyed substantial success in both Portugal and Poland.

The SAM Coupé, despite its commercial limitations, is widely regarded as a credible successor to the ZX Spectrum.

In India, Deci Bells Electronics Limited, based in Pune, introduced a licensed version of the Spectrum+ in 1988. Dubbed the "dB Spectrum+", it performed exceptionally well in the Indian market, selling over 50,000 units and capturing an 80% market share.

Unofficial Clones

Numerous unofficial Spectrum clones were manufactured, particularly in Eastern Europe. Many small companies in the Soviet Union assembled various clones, which were often distributed through poster advertisements and street stalls. In total, over 50 such clone models existed. In Czechoslovakia, the first production ZX Spectrum clone was the Didaktik Gama, featuring two switched 32 KB memory banks and 16 KB of slower RAM for graphical data output. This was followed by the Didaktik M, which later offered 5.25"/3.5" floppy disk drives, and the Didaktik Kompakt clone with an integrated floppy drive. Clones were also produced in South America, such as the Brazilian-made TK90X and TK95, as well as the Argentine Czerweny CZ models.

In the United Kingdom, ZX Spectrum peripheral vendor Miles Gordon Technology (MGT) launched the SAM Coupé 8-bit home computer in December 1989. It was designed for full compatibility with the ZX Spectrum 48K, featuring a Zilog Z80B processor clocked at 6 MHz and 256KB of RAM. By this time, the Amiga and Atari ST had firmly established their dominance in the market, leading to MGT's eventual receivership in June 1990. In his book Retro Tech, Peter Leigh considers the Sam Coupé to be the "true" successor of the ZX Spectrum.

Peripherals

Official peripherals included the ZX Printer, a compact spark printer that was available at the ZX Spectrum's launch. Its computer bus was partially backward-compatible with that of its predecessor, the ZX81. The printer utilized two electrically charged styli to burn away the surface of aluminium-coated paper, revealing the black underlay.

The ZX Interface 1, released in 1983, was an add-on module containing 8 KB of ROM, an RS-232 serial port, a proprietary local area network (LAN) interface known as ZX Net, and a port for connecting up to eight ZX Microdrives. These tape-loop cartridge storage devices, launched in July 1983, were noted for their speed, although they were not without reliability concerns. Sinclair Research also introduced the ZX Interface 2, which provided two joystick ports and a ROM cartridge port. While the ZX Microdrives initially received positive reviews, they never gained widespread popularity due to concerns about cartridge quality and potential piracy.

The Kempston interface, a third-party add-on for joysticks.

A wide array of third-party hardware add-ons became available throughout the machine's lifespan. These included the Kempston joystick interface, the Morex Peripherals Centronics/RS-232 interface, the Currah Microspeech unit for speech synthesis, the Videoface Digitiser, the SpecDrum drum machine, and the Multiface, a snapshot and disassembly tool from Romantic Robot. Following criticism of the original ZX Spectrum's rubber keyboard, external keyboards also gained popularity. In 1983, DK'Tronics launched a Light Pen compatible with certain drawing software.

The SPDOS and KDOS disk drive interfaces, developed by Abbeydale Designers/Watford Electronics, were bundled with office productivity software such as the Tasword word processor, Masterfile database, and Omnicalc spreadsheet. This software suite, along with OCP's Stock Control, Finance, and Payroll systems, introduced small businesses to streamlined computerized operations. In 1987 and 1988, Miles Gordon Technology released the DISCiPLE and +D systems, which offered the ability to store memory images as disk snapshots, allowing users to restore the Spectrum to its exact previous state. Both systems were compatible with Microdrive command syntax, simplifying the porting of existing software.

In the mid-1980s, Telemap Group introduced a fee-based service enabling ZX Spectrum users to connect their machines to the Micronet 800 information provider via a Prism Micro Products VTX5000 modem. Micronet 800, hosted by Prestel, offered news and information related to microcomputers, along with features for instant messaging and online shopping.

Software

Most Spectrum software was originally distributed on audio cassette tapes, designed for use with standard consumer cassette recorders. Software was also disseminated through type-in program listings published in magazines and books. Readers would manually enter a program and save it to cassette for later use. Some magazines even distributed 7" 331⁄3 rpm flexi discs, or "Floppy ROMs", a variant of regular vinyl records playable on a standard record player. Certain radio stations broadcast audio stream data via frequency modulation or medium wave, allowing listeners to record it directly onto audio cassettes. Specialized ZX Spectrum radio programs were broadcast in the United Kingdom, receivable over long distances on domestic radio receivers.

The software library for the machine was extensive, encompassing programming languages, databases, word processors (with Tasword being particularly prominent), spreadsheets, drawing and painting tools (such as OCP Art Studio), 3D modelling software (e.g., VU-3D), and even archaeology software. Over 24,000 unique software titles were released for the ZX Spectrum during its operational lifespan. Beginning in August 1982, the ZX Spectrum was bundled with Horizons: Software Starter Pack, a compilation featuring ten demonstration programs.

The ZX Spectrum boasts an extensive library of video games, solidifying its status as a prominent gaming platform throughout the 1980s. Notable titles include Manic Miner, Jet Set Willy, Chuckie Egg, Elite, Sabre Wulf, Knight Lore, and The Hobbit. Ant Attack is recognized as the first video game to feature isometric graphics. Turbo Esprit is credited as the first open world driving game, and Redhawk introduced the first superhero created specifically for a video game. Many ZX81 games were redeveloped for the Spectrum to leverage its enhanced colour and sound capabilities, such as Psion's Flight Simulation. The hardware limitations of the machine necessitated a high degree of creativity from video game designers.

Spectrum software was predominantly distributed on audio cassettes.

Reception

Initial reactions to the ZX Spectrum were largely favourable. Critics in Britain hailed the new machine as a worthy successor to the ZX81. Robin Bradbeer of Sinclair User praised the Spectrum's enhanced keyboard functions and lauded its "strong" ergonomic and presentable design. Tim Hartnell of Your Computer noted that Sinclair had addressed the shortcomings of the ZX80 and ZX81 by revamping the Spectrum's load and save functions, remarking that it made working with the machine "a pleasure." Hartnell concluded that, despite minor flaws, the machine was "way ahead" of its competitors and its specifications surpassed those of the BBC Micro Model A.

Terry Pratt of Computer and Video Games unfavourably compared the Spectrum's keyboard to the typewriter-style keys found on the BBC Micro, deeming it an improvement over the ZX81 but unsuitable for "typists." Similarly, David Tebbutt from Personal Computer World felt the Spectrum's keyboard felt more akin to a calculator than a typewriter, though he commended its functional versatility. Gregg Williams of BYTE also criticized the keyboard, stating that despite the machine's attractive price, the layout was "impossible to justify" and "poorly designed" in several aspects. Williams expressed skepticism regarding the computer's appeal to American consumers if priced at US $220, considering it "hardly competitive with comparable low-cost American units" and anticipating Timex would sell it for$ 125–150. A more critical review came from Jim Lennox of Technology Week, who wrote that "after using it [...] I find Sinclair's claim that it is the most powerful computer under £500 unsustainable. Compared to more powerful machines, it is slow, its colour graphics are disappointing, its BASIC limited and its keyboard confusing."

Legacy

"You cannot exaggerate Sir Clive Sinclair’s influence on the world [...] All your UK video game companies today were built on the shoulders of giants who made games for the ZX Spectrum." — Television presenter Dominik Diamond on Sinclair's death in 2021.

The ZX Spectrum's significant role in the history of personal computers and video games cemented its status as one of the most important and influential computers of the 1980s. Some observers credit it with initiating the British information technology industry during a period of economic recession, while simultaneously introducing home computing to the masses. As of 2024, it remains one of the best-selling British computers of all time, with over five million units sold by the time of its discontinuation in 1992. It held the title of Britain's top-selling computer until the Amstrad PCW surpassed it in the 1990s, having sold eight million units by the PCW's end-of-life in 1998. The ZX Spectrum is affectionately known as the "Speccy" by its devoted fanbase.

The ZX Spectrum found particular popularity in communist Czechoslovakia, with an estimated 100,000 units in the country by 1988, making it the most prevalent home computer at the time. This popularity was achieved despite its limited official distribution and lack of advertising. Its compact size facilitated easier smuggling into the country to circumvent high customs duties.

A number of notable game developers began their careers on the ZX Spectrum. Tim and Chris Stamper founded Ultimate Play the Game in 1982, achieving success with titles like Jetpac (1983), Atic Atac (1983), Sabre Wulf (1984), and Knight Lore (1984). The Stamper brothers later established Rare, which went on to become Nintendo's first Western third-party developer. David Perry, the founder of Shiny Entertainment, relocated from Northern Ireland to England specifically to focus on developing games for the ZX Spectrum.

Other developers renowned for their ZX Spectrum games include (in alphabetical order): Pete Cooke (Tau Ceti), Julian Gollop (Chaos, Rebelstar and the X-COM series), Jon Ritman (Match Day , Head Over Heels (game)), Mike Singleton (The Lords of Midnight, Doomdark's Revenge, War in Middle Earth), Jonathan "Joffa" Smith (Batman: The Caped Crusader, Mikie, Hyper Sports), Matthew Smith (Manic Miner, Jet Set Willy), Clive Townsend (Saboteur), The Oliver Twins (the Dizzy series), and Sandy White (Ant Attack, one of the earliest isometric games; I, of the Mask). Despite the system's limited audio capabilities (a single beeper), musicians such as David Whittaker, Tim Follin, and others managed to create impressive multichannel music for games.

Even today, hobbyists continue to develop software for the Spectrum using emulators. Several new games have been commercially released by modern software houses like Cronosoft. In 2020, a museum dedicated to Sinclair computers opened in Cantanhede, Portugal.

Recreations

In 2013, an FPGA-based clone known as the ZX Uno was announced. Its hardware, firmware, and software are all open source, released under a Creative Commons licence Share-alike. The use of a Spartan FPGA allows the system to emulate not only the ZX Spectrum but also numerous other 8-bit computers and game consoles. The Uno was successfully crowdfunded in 2016, with the first boards becoming available for purchase that same year.

In January 2014, Elite Systems, a company that produced a successful range of software for the original ZX Spectrum in the 1980s, announced plans for a Spectrum-themed Bluetooth keyboard designed to attach to mobile devices. The company utilized a crowdfunding campaign to fund the Recreated ZX Spectrum, which was intended to be compatible with games already released by Elite Systems on iTunes and Google Play. Elite Systems subsequently removed its Spectrum Collection application the following month due to complaints from authors of the original software regarding unpaid royalties. Wired UK described the finished product, styled as an original Spectrum 48k keyboard, as "absolutely gorgeous" but ultimately considered it more of an expensive novelty than a functional Spectrum. In July 2019, Eurogamer reported that many orders had yet to be fulfilled due to a dispute between Elite Systems and their manufacturer, Eurotech.

The ZX Spectrum Vega TV Game Console, manufactured by Retro Computers.

Later in 2014, the ZX Spectrum Vega retro video game console was announced by Retro Computers and crowdfunded on Indiegogo with the endorsement of Clive Sinclair. The Vega, released in 2015, took the form of a handheld TV game, but its lack of a full keyboard led to criticism from reviewers, particularly given the large number of text adventures included with the device. Most reviewers deemed the device cheaply made and uncomfortable to use. The follow-up, the ZX Spectrum Vega+, was designed as a handheld game console. Despite reaching its crowdfunding target in March 2016, the company failed to fulfill the majority of orders. Reviewing the Vega+, The Register criticized numerous aspects and features of the machine, including its design and build quality, concluding that the "entire feel is plasticky and inconsequential." Retro Computers Ltd was placed into liquidation in 2019.

The ZX Spectrum Next is an enhanced and updated version of the ZX Spectrum computer, implemented using FPGA technology. Funded via a Kickstarter campaign in April 2017, the board-only computer was delivered to backers later that year. The completed machine, including a case designed by Rick Dickinson (who passed away during the project's development), was released to backers in February 2020. MagPi described it as "a lovely piece of kit," noting its "well-designed and well-built: authentic to the original, and with technology that nods to the past while remaining functional and relevant in the modern age." PC Pro magazine called the Next "undeniably impressive" while acknowledging that some features were "not quite ready." A further Kickstarter campaign for an improved revision of the hardware was successfully funded in August 2020.

The ZX Touch is a handheld gaming console released by Elmar Electronic in November 2023, utilizing bare-metal emulation for playing ZX Spectrum games. It features a 7-inch touchscreen, built-in games, and microSD support for loading additional titles.

In August 2024, Retro Games announced the upcoming release of a ZX Spectrum recreation titled "The Spectrum," which will include 48 built-in games, a save game option, rewind functionality, and the ability to load pre-owned titles. It is scheduled for release on 22 November 2024.

In Popular Culture

A recurring gag in the film Scott Pilgrim vs. the World features character Julie Powers being censored with ZX Spectrum sound effects. Director Edgar Wright stated that he used to wait for Spectrum games to load during his teenage years.

On 23 April 2012, a Google doodle commemorated the 30th anniversary of the Spectrum. Coinciding with St George's Day, the Google logo depicted St George fighting a dragon in the style of a Spectrum loading screen.

One of the alternate endings in the interactive film Black Mirror: Bandersnatch (2018) includes the main character playing data tape audio that, when loaded into a ZX Spectrum emulator, generates a QR code leading to a website featuring a playable version of the "Nohzdyve" game from the film.