A standard set of 128 sounds for MIDI sound cards and devices (synthesizers, sound modules, etc.). By assigning instruments to specific MIDI patch locations, General MIDI provides a standard way ...

to conform to a particular MIDI sound card or module. The keyboard map is used to assign values to non-standard keyboard keys. The patch map assigns sounds to an instrument number (see MIDI patch).

Before the AdLib sound card, sound on PCs was in a terrible shape. Since the dawn of IBM, all PCs included a speaker, but this PC speaker was only capable of sounding one note at a time.