Yamaha OPL2/OPL3 FM synthesis channels (varies by card)
Sound Blaster 8/16-bit PCM playback channel
General MIDI or MT-32 output (external)
DOS game audio varied wildly depending on the sound card. Common configurations include the Yamaha OPL2/OPL3 FM synth (AdLib / Sound Blaster), Sound Blaster PCM for digitized audio, and Roland MT-32 / General MIDI for higher-end MIDI playback.