SN76489

This programmable sound generator (PSG) arrived from Texas Instruments around 1980: three square-wave channels plus one noise channel, driven by a handful of registers. Its simplicity made it cheap and ubiquitous — the TI-99/4A, ColecoVision, SG-1000, Sega Master System and Game Gear, the IBM PCjr and Tandy 1000, and the BBC Micro.

The sound is unmistakable: hard, unfiltered square waves, a world away from the SID's synthesis. In the Sega Mega Drive it lived on beside the YM2612 FM chip, and its register writes are still captured in the VGM format. Compare the AY-3-8910, a contemporary rival of near-identical design.