ZX Spectrum

2007 Schools Wikipedia Selection. Related subjects: Computing hardware and infrastructure

The original 1982 ZX Spectrum.
ZX Spectrum
Type Home computer
Released April 1982
Discontinued December 1990
Processor Z80 @ 3.5 MHz and equivalent
Memory 16 kB / 48 kB / 128 kB
OS Sinclair BASIC

The ZX Spectrum is a home computer released in the United Kingdom in 1982 by Sinclair Research Ltd. Originally dubbed the ZX82, the machine was later renamed the ZX Spectrum by Sinclair to highlight the machine's colour display, compared to the black-and-white of its predecessor, the Sinclair ZX81.

The Spectrum was the first mainstream audience home computer in the UK, similar in significance to the Commodore 64 in the USA; the C64 was the main rival to the Spectrum in the UK market during the early 1980s.

In 1980–82 the UK Department of Education and Science had begun the Microelectronics Education Programme to introduce microprocessing concepts and educational materials. In 1982 through to 1986, the Department of Industry (DoI) allocated funding to assist UK local education authorities to supply their schools with a range of computers, with the ZX Spectrum proving useful for the control projects.


ZX Spectrum 48K motherboard (Issue 3B — 1983)
ZX Spectrum 48K motherboard (Issue 3B — 1983)

The Spectrum's hardware was designed by Richard Altwasser of Sinclair Research. Sinclair's industrial designer Rick Dickinson was responsible for the machine's outward appearance.

Based on a Zilog Z80A CPU running at 3.5  MHz, the original Spectrum came with either 16  kB or 48 kB of RAM. Both units had 16 kB of ROM.

The Spectrum's video output was through an RF modulator and was designed for use with contemporary portable television sets, for a simple colour graphic display. Text could be displayed using 32 columns × 24 rows of characters from the ZX Spectrum character set, with a choice of 8 colours in either normal or bright mode, which gave 15 shades (black was the same in both modes). The image resolution was 256×192 with the same colour limitations. The Spectrum had an interesting method of handling colour; the colour attributes were held in a 32×24 grid, separate from the text or graphical data, but was still limited to only two colours in any given character cell, both of which had to be either bright or non-bright. This led to what was called colour clash or attribute clash with some bizarre effects in arcade style games. This problem became a distinctive feature of the Spectrum and an in-joke among Spectrum users, as well as a point of derision by advocates of other systems. Other machines available around the same time, for example the Amstrad CPC, did not suffer from this problem. The Commodore 64 used colour attributes, but hardware sprites and scrolling were used to avoid attribute clash.

Sound output was through a beeper on the machine itself. This was capable of producing one channel with 10 octaves over ten semitones. The machine also included an expansion bus edge connector and audio in/out ports for the connection of a cassette recorder for loading and saving programs and data.

The machine's software was written by Steve Vickers on contract from Nine Tiles Ltd, the authors of Sinclair BASIC. The Spectrum's chiclet keyboard (on top of a membrane, similar to calculator keys) was marked with Sinclair BASIC keywords, so that, for example, pressing "G" when in programming mode would insert the BASIC command GO TO.


Sinclair Research models

The original ZX Spectrum is remembered for its rubber keyboard and diminutive size. It was originally released in 1982 with 16 kB of RAM for GB£125 or with 48 kB for £175; these prices were later reduced to £99 and £129 respectively. Owners of the 16 kB model could purchase an internal 32 kB RAM upgrade daughterboard, which consists of 8 dynamic RAM chips and a few TTL chips. Users could mail their 16K Spectrums to Sinclair to be upgraded to 48 kB versions. To reduce the price, the 32 kB extension actually comprised eight faulty 64  kilobit chips with only one half of their capacity working and/or available. External 32 kB RAMpacks that mounted in the rear expansion slot were also available from third parties. As with the ZX81, "RAMpack wobble" caused by poor connection with the expansion was a frequent problem for many users, causing instant crashes and sometimes ULA or CPU burnout. Both machines had 16kB of onboard ROM.

ZX Spectrum+
ZX Spectrum+

Planning of the ZX Spectrum+ started in June 1984, and was released in October the same year. This 48 kB Spectrum (development code-name TB) introduced a new QL-style enclosure with a much needed injection-moulded keyboard and a reset button, retailing for £179.95. A DIY conversion-kit for older machines was also available. Early on, the machine outsold the rubber-key model 2:1; however, some retailers reported very high failure rates.

ZX Spectrum 128
ZX Spectrum 128

Sinclair developed the ZX Spectrum 128 (code-named Derby) in conjunction with their Spanish distributor Investrónica. Investrónica had helped adapt the ZX Spectrum+ to the Spanish market after the Spanish government introduced a special tax on all computers with 64 kB RAM or less which did not support the Spanish alphabet (including ñ) and show messages in Spanish.

New features included 128 kB RAM, three-channel audio via the AY-3-8912 chip, MIDI compatibility, an RS-232 serial port, an RGB monitor port, 32 kB of ROM including an improved BASIC editor and an external keypad.

The machine was simultaneously presented for the first time and launched in September 1985 at the SIMO '85 trade show in Spain, with a price of 44.250 pesetas (266). Because of the large amount of unsold Spectrum+ models, Sinclair decided not to start selling in the UK until January 1986 at a price of £179.95. No external keypad was available for the UK release, although the ROM routines to utilise it and the port itself, which was hastily renamed "AUX", remained.

The Z80 processor used in the Spectrum has a 16-bit address bus, which means only 64 kB of memory can be addressed. To facilitate the extra 80 kB of RAM the designers utilised a bank switching technique so that the new memory would be available as six pages of 16 kB at the top of the address space. The same technique was also used to page 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 out abilities were exposed to the BASIC programming language with the command PLAY and a new command SPECTRUM was added to switch the machine into 48K mode. To enable BASIC programmers to access the additional memory, a RAM disk was created where files could be stored in the additional 80 kB of RAM. The new commands took the place of two existing user-defined-character spaces causing compatibility issues with some BASIC programs.

The Spanish version had the "128K" logo (right, bottom of the computer) in white colour while the English one had the same logo in red colour.

Amstrad models

ZX Spectrum +2
ZX Spectrum +2

The ZX Spectrum +2 was Amstrad's first Spectrum, coming shortly after their purchase of the Spectrum range and "Sinclair" brand in 1986. The machine featured an all-new grey enclosure featuring a spring-loaded keyboard, dual joystick ports, and a built-in cassette recorder dubbed the "Datacorder" (like the Amstrad CPC 464), but was (in all user-visible respects) otherwise identical to the ZX Spectrum 128. Production costs had been reduced and the retail price dropped to £139–£149.

The new keyboard did not include the BASIC keyword markings that were found on earlier Spectrums, except for the keywords LOAD, CODE and RUN which were useful for loading software. However, the layout remained identical to that of the 128.

ZX Spectrum +3
ZX Spectrum +3

The ZX Spectrum +3 looked similar to the +2 but featured a built-in 3-inch floppy disk drive (like the Amstrad CPC 6128) instead of the tape drive. It was launched in 1987, initially retailed for £249 and then later £199 and was the only Spectrum capable of running the CP/M operating system without additional hardware.

The +3 saw the addition of two more 16 kB ROMs, now physically implemented as two 32 kB chips. One was home to the second part of the reorganised 128 ROM and the other hosted the +3's disk operating system. This was a modified version of Amstrad's AMSDOS, called +3DOS. To facilitate the new ROMs and CP/M, the bank-switching was further improved, allowing the ROM to be paged out for another 16 kB of RAM.

Such core changes brought incompatibilities:

  • Removal of several lines on the expansion bus edge connector (video, power, ROMCS and IORQGE); caused many external devices problems; some such as the VTX5000 modem could be used via the "FixIt" device
  • Reading a non-existent I/O port no longer returned the last attribute; caused some games such as Arkanoid to be unplayable
  • Memory timing changes; some of the RAM banks were now contended causing high-speed colour-changing effects to fail
  • The keypad scanning routines from the ROM were removed

Some older 48K, and a few older 128K, games were incompatible with the machine.

The +3 was the final official model of the Spectrum to be manufactured, remaining in production until December 1990. Although still accounting for one third of all home computer sales at the time, production of the model was ceased by Amstrad in an attempt to transfer customers to their CPC range.

ZX Spectrum +2A.
ZX Spectrum +2A.

The ZX Spectrum +2A was produced to homogenise Amstrad's range in 1987. Although the case reads "ZX Spectrum +2", the +2A/B is easily distinguishable from the original +2 as the case was restored to the standard Spectrum black.

The +2A was derived from Amstrad's +3 4.1 ROM model, using a new motherboard which vastly reduced the chip count, integrating many of them into a new ASIC. The +2A replaced the +3's disk drive and associated hardware with a tape drive, as in the original +2. Originally, Amstrad planned to introduce an additional disk interface, but this never appeared. If an external disk drive was added, the "+2A" on the system OS menu would change to a +3. As with the ZX Spectrum +3, some older 48K, and a few older 128K, games were incompatible with the machine.

The ZX Spectrum +2B signified a manufacturing move from Hong Kong to Taiwan later in 1987.


Sinclair licensed the Spectrum design to Timex Corporation in the United States. An enhanced version of the Spectrum with better sound, graphics and other modifications was marketed in the USA by Timex as the Timex Sinclair 2068. Timex's derivatives were largely incompatible with Sinclair systems. However, some of the Timex innovations were later adopted by Sinclair Research. A case in point was the abortive Pandora portable Spectrum, whose ULA had the high resolution video mode pioneered in the TS2068. Pandora had a flat-screen monitor and Microdrives and was intended to be Sinclair's business portable until Alan Sugar bought the computer side of Sinclair, when he took one look at it and ditched it (a conversation with UK computer journalist Guy Kewney went thus: AS: "Have you seen it?" GK: "Yes" AS: "Well then.").

In the UK, Spectrum peripheral vendor Miles Gordon Technology (MGT) released the SAM Coupé as a potential successor with some Spectrum compatibility. However, by this point, the Commodore Amiga and Atari ST had taken hold of the market, leaving MGT in eventual receivership.

Many unofficial Spectrum clones were produced, especially in Eastern Bloc nations and South America (e.g. Microdigital TK 90X). In Russia for example, ZX Spectrum clones were assembled by thousands of small start-ups and distributed though poster ads and street stalls. Over 50 such clone models existed. Some of them are still being produced, such as the Sprinter and ATM Turbo.


Several peripherals for the Spectrum were marketed by Sinclair: the ZX Printer was already on the market, as the ZX Spectrum expansion bus was backwards-compatible with that of the ZX81.

The ZX Interface 1 add-on module included 8 kB of ROM, an RS-232 serial port, a proprietary LAN interface (called ZX Net), and an interface for the connection of up to eight ZX Microdrives — somewhat unreliable but speedy tape-loop cartridge storage devices released in July 1983. These were later used in a revised version on the Sinclair QL, whose storage format was electrically compatible but logically incompatible with the Spectrum's. Sinclair also released the ZX Interface 2 which added two joystick ports and a ROM cartridge port.

Kempston joystick interface.
Kempston joystick interface.

There were also a plethora of third-party hardware addons. The better known of these included the Kempston joystick interface, the Morex Peripherals Centronics/RS-232 interface, the Currah Microspeech unit (speech synthesis), Videoface Digitiser, RAM pack, and Cheetah Marketing SpecDrum (Drum machine), and the Multiface (snapshot and disassembly tool), from Romantic Robot.

There were numerous disk drive interfaces, including the Abbeydale Designers/ Watford Electronics SPDOS, Abbeydale Designers/ Kempston KDOS and Opus Discovery. The SPDOS and KDOS interfaces were the first to come bundled with Office productivity software ( Tasword Word Processor, Masterfile database and OmniCalc spreadsheet). This bundle, together with OCP's Stock Control, Finance and Payroll systems, introduced many small businesses to a streamlined, computerised operation. The most popular floppy disk systems (except in East Europe) were the DISCiPLE and +D systems released by Miles Gordon Technology in 1987 and 1988 respectively. Both systems had the ability to store memory images onto disk snapshots could later be used to restore the Spectrum to its exact previous state. They were also both compatible with the Microdrive command syntax, which made porting existing software much simpler.

During the mid- 1980s, the company Micronet800 launched a service allowing users to connect their ZX Spectrums to a network known as Micronet hosted by Prestel. This service had some similarities to the Internet, but was proprietary and fee-based.


The Spectrum enjoys a vibrant, dedicated fan-base. Since it was cheap and simple to learn to use and program, the Spectrum was the starting point for many programmers and technophiles who remember it with nostalgia. The hardware limitations of the Spectrum imposed a special level of creativity on game designers, and for this reason, many Spectrum games are very creative and playable even by today's standards.

The Spectrum family enjoyed a very large software library of at least 13,000 titles. Though Spectrum hardware was limited by modern standards, its software library was very diverse, including programming language implementations, databases (eg: VU-File), word processors (eg: Tasword II), spreadsheets (eg: VU-Calc), drawing and painting tools (eg: James Hutchby's OCP Art Studio, Artist, Paintbox, Melbourne Draw), even 3D modelling. A huge quantity of games were released for the system.


Most Spectrum software was originally distributed on audio cassette tapes. The Spectrum was intended to work with almost any cassette tape player, and despite differences in audio reproduction fidelity, the software loading process was quite reliable.

While the ZX Microdrive quickly became quite popular with the Spectrum user base due to the low cost of the drives, the actual media was very expensive for software publishers to use for mass market releases (by a factor of 10× compared to tape duplication). Furthermore, the cartridges themselves acquired a reputation for unreliability, and publishers were reluctant to QA each and every item shipped. Hence the main use became to complement tape releases, usually utilities and niche products like the Tasword word processing software and the aforementioned Trans Express. No games are known to be exclusively released on Microdrive.

Despite the popularity of the DISCiPLE and +D systems, most software released for them took the form of utility software. The ZX Spectrum +3 enjoyed much more success when it came to commercial software releases on floppy disk. More than 700 titles were released on 3-inch disk from 1987 to 1997.

Software was also distributed through print media, fan magazines and books. The prevalent language for distribution was the Spectrum's BASIC dialect Sinclair BASIC. The reader would type the software into the computer by hand, run it, and save it to tape for later use. The software distributed in this way was in general simpler and slower than its assembly language counterparts, and lacked graphics. But soon, magazines were printing long lists of checksummed hexadecimal digits with machine code games or tools. There was a vibrant scientific community built around such software, ranging from satellite dish alignment programs to school classroom scheduling programs.

Another, unusual, software distribution method was to broadcast the audio stream from the cassette on another medium and have users record it onto an audio cassette themselves. In radio or television shows in e.g. Belgrade ( Ventilator 202), Poland, Czechoslovakia, Romania or Brazil, the host would describe a program, instruct the audience to connect a cassette tape recorder to the radio or TV and then broadcast the program over the airwaves in audio format. Some magazines distributed 7" 33⅓ rpm "flexidisc" records, a variant of regular vinyl records, which could be played on a standard record player. These disks were known as " floppy ROMs".

Copying and backup software

Most copier software available for the Spectrum was designed for copyright infringement of software through tape duplication. Copiers were developed to copy programs from audio tape to microdrive tapes, and later on diskettes. Complex loaders with unusual speeds or encoding were the basis of the Spectrum's copy prevention schemes, although other methods were used including asking for a particular word from the documentation included with the game — often a novella — or another physical device distributed in the software box. As protection became more complex it was almost impossible to use copiers to copy tapes, and the loaders had to be cracked by hand, to produce unprotected versions. Special hardware such as Romantic Robot's Multiface was able to dump a copy of the ZX Spectrum RAM to disk/tape at the press of a button, entirely circumventing the copy protection systems.

Most Spectrum software has been digitized in recent years and is available for download in digital form. One popular program for digitizing Spectrum software is Taper: it allows connecting a cassette tape player to the line in port of a sound card or, through a simple home-built device, to the parallel port of a PC. Once in digital form, the software can be executed on one of many existing emulators, on virtually any platform available today. Today, the largest on-line archive of ZX Spectrum software is World of Spectrum, with more than 12,000 titles. The legality of this practice is still in question. However, it seems unlikely that any action will ever be taken over such so-called abandonware.

Famous Spectrum developers

A number of current leading games developers and development companies began their careers on the ZX Spectrum, including Peter Molyneux (ex- Bullfrog Games), David Perry of Shiny Entertainment, and Ultimate Play The Game (now known as Rare, maker of many famous titles for Nintendo game consoles). Other prominent games developers include Matthew Smith ( Manic Miner, Jet Set Willy), and Jon Ritman ( Match Day, Head Over Heels) and Sid Meier ( Silent Service)


Retrieved from " http://en.wikipedia.org/wiki/ZX_Spectrum"