Sinclair ZX Spectrum

The ZX Spectrum was a home computer released in the United Kingdom in 1982 by Cambridge-based Sinclair Research Ltd. Although it was originally called the ZX82, it was later renamed the ZX Spectrum to highlight the machine's colour display, in comparison to the monochrome displays of its predecessors, the ZX80 and ZX81. The ZX Spectrum remained in production until December 1990; although still accounting for one third of all home computer sales at the time, production of the model was stopped by Amstrad (who had by then bought the rights to Sinclair products) in an attempt to transfer customers to their CPC range.

Models

There were a number of ZX Spectrum models developed from its original release in 1982 to the time it was discontinued at the end of 1990.

ZX Spectrum (1982)

Based on a Zilog Z80A CPU running at 3.5 MHz, the original Spectrum came with either 16 kB or 48 kB of RAM. Owners of the cheaper 16 kB model could purchase an internal 32 kB RAM upgrade daughterboard, or post their machines to Sinclair to be upgraded to a 48 kB version. External 32 kB RAM packs that mounted in the rear expansion slot were also available from third parties. Both machines had 16 kB of onboard ROM.

Video output was designed for use with contemporary portable television sets through an RF modulator, and gave a simple colour graphic display. Text could be displayed using 32 columns x 24 rows of characters with a choice of eight colours at two levels of brightness.

Sound output was through a beeper on the unit itself, which was capable of producing one channel with 10 octaves over ten semitones. There was also a rubber keyboard marked with Sinclair BASIC keywords, so that, for example, pressing "G" when in programming mode would insert the BASIC command GO TO. The machine also included audio in/out ports and an expansion bus edge connector for the connection of a cassette recorder for loading and saving programs and data.

ZX Spectrum+ (1984)

Released in October 1984, the 48 kB Spectrum+ included an injection-moulded keyboard and a reset button, and a conversion-kit for older machines was also available. Although the new machine outsold the rubber-key model 2:1, some retailers reported high failure rates.

ZX Spectrum 128 (1985)

The ZX Spectrum 128 was developed in conjunction with the unit's Spanish distributor Investrenica, and featured 128 kB RAM, 32 kB of ROM including an improved BASIC editor, three-channel audio via the AY-3-8912 chip, an external keypad (not in the UK), MIDI compatibility, an RS-232 serial port and an RGB monitor port.

As the Z80 processor had a 16-bit address bus, only 64 kB of memory could be addressed. In order to facilitate the extra 80 kB of RAM the designers used 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. 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 problems with some BASIC programs.

Due to the high number of unsold Spectrum+ models, Sinclair decided not to sell the machine in the UK until January 1986.

ZX Spectrum +2 (1986)

In April 1986, Amstrad bought the rights to the Sinclair brand and Spectrum range, and soon released the ZX Spectrum +2, which was identical to the ZX Spectrum 128 apart from cosmetic changes and the addition of peripherals. These changes included a new grey enclosure featuring a spring-loaded keyboard, a built-in cassette recorder and dual joystick ports. The new keyboard did not include the BASIC keyword markings that were found on earlier models, except for the keywords RUN, LOAD and CODE, which were useful for loading software.

ZX Spectrum +3 (1987)

Although the ZX Spectrum +3 looked similar to the +2, it also featured a built-in 3-inch floppy disk drive instead of the tape drive. It was the only Spectrum capable of running the CP/M operating system without additional hardware.

The +3 also saw the addition of two more 16 kB ROMs, which were physically implemented with the existing 16 kB 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. 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.

However, such core changes brought incompatibilities and some older 48K games and a few older 128K games were incompatible with the machine.

Games

ZX Spectrum software library was extremely wide and diverse, comprising of over 13,000 titles. Most Spectrum software was originally distributed on audio cassette tapes, which could be played with almost any cassette tape player. The software was encoded on tape as a sequence of pulses that sounded similar to a modern day modem, and one way of distributing cassette programs was by broadcasting the audio stream, with the audience connecting a tape recorder to the radio or TV and taping the signal.

The ZX Microdrive was a tape-loop data storage system launched in July 1983, which used tiny (44 x 34 x 8 mm including protective cover) cartridges containing a 5 metre loop of video tape. However, although the Microdrive became popular with users due to the low price of the drives, the cartridges themselves cost 10 times more to produce, and acquired a reputation for unreliability. No games were ever released exclusively on Microdrive.

The ZX Spectrum +3 also featured a built-in 3-inch disk drive, which enjoyed great success with over 700 software titles released for it from 1987 to 1997.

As the ZX Spectrum was cheap and simple to learn to use and program, many people enjoyed programming their own games by typing in Spectrum's BASIC dialect and saving it to tape for later use.

Some of the most popular titles released for the ZX Spectrum included: