The PSG chip family is composed of 3 variants: the AY-3-8910 with two 8-bit I/O ports, the AY-3-8912 with one 8-bit I/O port and the AY-3-8913 with no I/O port. In addition to the CPC, these chips were also used in the [[ZX Spectrum]], [[MSX]], [[Oric]], [[Vectrex]] and [[Intellivision]].
Yamaha produced a derivative SSG (Software-controlled Sound Generator) chip family(YM2149F, YM3439, YMZ294, YM284, YMZ285). This chip equips the [[Atari ST]]. The main difference is that the envelope counter on the PSG has 16 steps. On the SSG it has twice the steps, happening twice as fast.
The SSG has also been integrated as a component inside some of the arcade soundchips of the Yamaha OPN family. That's why you can find it in the [[Neo-Geo]] as a component inside the YM2610 soundchip.