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Tracing the History of the Computer - Sinclair ZX Spectrum


Sinclair ZX Spectrum

Sinclair ZX Spectrum 48k

The Sinclair ZX Spectrum was a home computer released in the United Kingdom in 1982 by Sinclair Research. Based on a Zilog Z80 CPU running at 3.50 MHz, the Spectrum came with either 16 KB or 48 KB of RAM.

The hardware designer was Richard Altwasser of Sinclair Research and the software was written by Steve Vickers on contract from Nine Tiles Ltd, the authors of Sinclair BASIC. Sinclair's industrial designer Rick Dickinson was responsible for the machine's outward appearance. Originally dubbed the ZX82, the machine was later renamed the "Spectrum" by Sinclair to highlight the machine's colour display, compared to the black-and-white of its predecessors, the ZX80 and ZX81.


Video output was to a TV, for a simple colour graphic display. The rubber 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. Experienced programmers were thus able to create BASIC programs much faster than on other computers at the time. Programs and data were stored using a normal cassette recorder.

The Spectrum's video display, although rudimentary by today's standards, was perfect at the time for display on portable TV sets, and did not present much of a barrier to game development. Text could be displayed using 32 columns x 24 rows of characters from the 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 256x192 with the same colour limitations. The Spectrum had an interesting method of handling colour; the colour attributes were held in a 32x24 grid, separate from the text or graphical data, but was still limited to only two colours in any given character cell. 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.

The Spectrum was the first mainstream audience home computer in the UK, similar in significance to the Commodore 64 in the USA. The Commodore 64, often abbreviated to C64, was also the main rival to the Spectrum in the UK market. An enhanced version of the Spectrum with better sound, graphics and other modifications was marketed in the USA by the Timex Corporation as the TS2068.


Educational application

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; the ZX Spectrum was very useful for the control projects.


ZX Spectrum 16K/48K (1982)

Released by Sinclair in 1982 and available with either 16 kB (£125, later £99) or 48 kB (£175, later £129) of RAM and 16 kB ROM, the original ZX Spectrum is remembered for its rubber keyboard and diminutive size. Owners of the 16 kB model could purchase an internal 32 kB RAM upgrade daughterboard, which consists of 8 dynamic RAMs and few TTL chips. Users could mail their 16K Spectrums to Sinclair to be upgraded to 48K versions. To reduce the price, 32 kB extension was actually comprised of 8 faulty 64 kilobit chips with only one half of their capacity working and/or available.

Also available were third-party external 32 kB RAMpacks that mounted in the rear expansion slot. As with the ZX81, "RAMpack wobble" caused by poor connection with the expansion was the bane of many users, causing instant crashes and sometimes ULA or CPU burnout.

ZX Spectrum+ (1984)

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 £180. An upgrade package for older machines was also available. Most hard core users (programmers and gamers) disliked the new keyboard.

ZX Spectrum 128 (1986)

Sinclair developed the 128 (code-named Derby) in conjunction with their Spanish distributor Investrónica. Investrónica had helped adapt the ZX Spectrum+ to the Spanish market after Spanish courts decreed all computers with 64 kB RAM or less must 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.

ZX Spectrum +2 (1986)

The +2 was Amstrad's first Spectrum, coming shortly after their purchase of the Spectrum range and "Sinclair" brand. 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 (1987)

The 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 initially retailed for £249 and then later £199 and was the only Spectrum capable of running CP/M without additional hardware.

The +3 saw the addition of two more 16K ROMs, now physically implemented as two 32K chips. One was home to the second part of the reorganised 128K ROM and the other hosted the +3's disk operating system. 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 as well as offering three 16 KB pages for the display RAM.

The ZX Spectrum +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 /+2B (1987)

The +2A was produced to homogenise Amstrad's range. 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, hosting 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 +2B signified a manufacturing move from Hong Kong to Taiwan.


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