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 × 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 Investrónica, 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 origin...