ZX Spectrum

ZX Spectrum
ZXSpectrum48k.jpg
An issue 2 1982 ZX Spectrum
Developer Sinclair Research Ltd
Manufacturer Timex Corporation
Type Home computer
Generation 8-bit
Release date United Kingdom: 23 April 1982; 34 years ago (1982-04-23)
Retail availability 1982–1992
Discontinued 1992 [1]
Units sold 5 million (not including clones)
Media Cassette tape, 3-inch floppy disk on Spectrum +3
Operating system Sinclair BASIC
CPU Z80 @ 3.5 MHz and equivalent
Memory 16  KB / 48 KB / 128 KB
Predecessor ZX81
Successor QL

The ZX Spectrum ( UK /zɛd ɛks ˈspɛktrəm/) is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research Ltd. It was manufactured in Dundee, Scotland, in the now closed Timex factory. [2]

Referred to during development as the ZX81 Colour and ZX82, [3] [4] it was launched as the ZX Spectrum by Sinclair to highlight the machine's colour display, compared with the black and white of its predecessor, the ZX81. [5] The Spectrum was released as eight different models, ranging from the entry level with 16  KB RAM released in 1982 to the ZX Spectrum +3 with 128 KB RAM and built in floppy disk drive in 1987; together they sold in excess of 5 million units worldwide (not counting clones). [6]

The Spectrum was among the first mainstream-audience home computers in the UK, similar in significance to the Commodore 64 in the USA. The introduction of the ZX Spectrum led to a boom in companies producing software and hardware for the machine, [7] the effects of which are still seen; [1] some credit it as the machine which launched the UK IT industry. [8] Licensing deals and clones followed, and earned Clive Sinclair a knighthood for "services to British industry". [9]

The Commodore 64, Dragon 32, Oric-1 and Atmos, BBC Microcomputer and later the Amstrad CPC range were rivals to the Spectrum in the UK market during the early 1980s. Over 24,000 software titles have been released since the Spectrum's launch and new titles continue to be released—over 100 in 2012. [10] In 2014, a Bluetooth keyboard modelled on the Spectrum was announced. [11]

Hardware

ZX Spectrum 48K motherboard (Issue 3B — 1983, heat sink removed)

The Spectrum is based on a Zilog Z80 A CPU running at 3.5  MHz (or NEC D780C-1 clone). The original model has 16 KB (16×1024 bytes) of ROM and either 16 KB or 48 KB of RAM. Hardware design was by Richard Altwasser of Sinclair Research, and the outward appearance was designed by Sinclair's industrial designer Rick Dickinson. [7]

Video output is through an RF modulator and was designed for use with contemporary portable television sets, for a simple colour graphic display. Text can be displayed using 32 columns × 24 rows of characters from the ZX Spectrum character set or from a set provided within an application, from a palette of 15 shades: seven colours at two levels of brightness each, plus black. [12] The image resolution is 256×192 with the same colour limitations. [13] To conserve memory, colour is stored separate from the pixel bitmap in a low resolution, 32×24 grid overlay, corresponding to the character cells. In practice, this means that all pixels of an 8x8 character block share one foreground colour and one background colour. Altwasser received a patent for this design. [14]

An "attribute" consists of a foreground and a background colour, a brightness level (normal or bright) and a flashing "flag" which, when set, causes the two colours to swap at regular intervals. [13] This scheme leads to what was dubbed colour clash or attribute clash, where a desired colour of a specific pixel could not necessarily be selected. This became a distinctive feature of the Spectrum, meaning programs, particularly games, had to be designed around this limitation. Other machines available around the same time, for example the Amstrad CPC or the Commodore 64, did not suffer from this limitation. The Commodore 64 used colour attributes in a similar way, but a special multicolour mode, hardware sprites and hardware scrolling were used to avoid attribute clash. [15]

Sound output is through a beeper on the machine itself, capable of producing one channel with 10 octaves. Software was later available that could play two channel sound. The machine includes an expansion bus edge connector and 3.5 mm audio in/out ports for the connection of a cassette recorder for loading and saving programs and data. The "ear" port can drive headphones and the "mic" port provides line level [16] audio out which could be amplified.