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.
Yamaha produced a derivative SSG (Software-controlled Sound Generator) chip family. This chip equips the [[Atari ST]]. The main difference between the SSG and the PSG is that the internal volume control of the D/A converter has 32 levels instead of 16.
The SSG has also been integrated as a component inside every chip of the Yamaha OPN family.