The Sinclair ZX Spectrum is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research Ltd. Referred to during development as the ZX81 Colour and ZX82,the machine 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 Sinclair ZX81.
The Spectrum was among the first mainstream audience home computers in the UK, similar in significance to the Commodore 64 in the USA; the C64 was a major rival to the Spectrum in the UK market during the early 1980s (The BBC Microcomputer was another major competitor). The introduction of the ZX Spectrum led to a boom of companies producing software and hardware for it. The effects of this are still seen.
Disregarding the Covox, Soundrive and Digital Sound addons for the new ZX Spectrum clones (the last one of which can play four-channel Amiga .mods), there are just two ways to let Spectrum produce sound, depending on it's model.
ZX Spectrum 16K and 48K all featured a one-bit speaker. Many beeper music engines has been created since, to make richer music that still fits under the machine's limitations but consumes a lot of CPU - see zxbeep (format)
for the complete list.
ZX Spectrum 128K and more advanced models from here on featured the three-channel AY-3-8910 chip, although it can also be used on 48K with the help of Fuller Joystick or custom added AY. Some Spectrum clones use its' analog, YM2149F, instead. Those two music chips were already used on so many home computers they've became one format of their own - see aym (format)