[1] PSGs are controlled by writing data to dedicated registers on the chip via an external CPU; hence the name programmable sound generator.
One or more basic waveforms are generated (typically a square, triangle or saw-tooth wave) and often a noise signal.
PSGs were partly developed as a way of incorporating relatively complex sounds at a low cost.
In the same year Atari designed the POKEY chip for its home computers and game systems.
[4] The main chip in the Nintendo Entertainment System, the Ricoh 2A03, included a PSG.