Sinclair ZX Spectrum

The ZX Spectrum is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research Ltd. The machine was named Spectrum by Sinclair to highlight the machine’s color display, compared with the black-and-white of its predecessor, the ZX81. The Spectrum was ultimately released as eight different models, ranging from the entry level model 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 numerous clones). 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, the effects of which are still seen; some credit it as the machine which launched the UK IT industry. Licensing deals and clones followed, and earned Clive Sinclair a knighthood for “services to British industry”.

The Spectrum is based on a Zilog Z80A CPU running at 3.5 MHz (or NEC D780C-1 clone). The original model Spectrum 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 machine’s outward appearance was designed by Sinclair’s industrial designer Rick Dickinson. Video output is through an RF modulator and was designed for use with contemporary portable television sets, for a simple color 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 colors at two levels of brightness each, plus black. The image resolution is 256×192 with the same colour limitations. To conserve memory, color 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 8×8 character block share one foreground color and one backgroundcolor. Altwasser received a patent for this design.

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