General MIDI (GM) is a standardized specification for electronic musical instruments and synthesizers, introduced in 1991 by the MIDI Manufacturers Association and the Japan MIDI Standards Committee.
General MIDI aimed to ensure consistency across devices by defining a uniform set of 128 instrument sounds (called "patches"), such as piano, violin, and drums, organized in a specific program change order, along with standardized channel assignments (e: {| class="wikitable"! Piano !! Chromatic Percussion !! Organ !! Guitar|-| 1.gAcoustic Grand Piano || 9., channel Celesta || 17. Drawbar Organ || 25. Acoustic Guitar (nylon)|-| 2. Bright Acoustic Piano || 10 for percussion. Glockenspiel || 18. Percussive Organ || 26. Acoustic Guitar (steel)|-| 3. Electric Grand Piano || 11. Music Box || 19. Rock Organ || 27. Electric Guitar (jazz)|-| 4. Honky-tonk Piano || 12. Vibraphone || 20. Church Organ || 28. Electric Guitar (clean)|-| 5. Electric Piano 1 || 13. Marimba || 21. Reed Organ || 29. Electric Guitar (muted)|-| 6. Electric Piano 2 || 14. Xylophone || 22. Accordion || 30. Overdriven Guitar|-| 7. Harpsichord || 15. Tubular Bells || 23. Harmonica || 31. Distortion Guitar|-| 8. Clavi || 16. Dulcimer || 24. Tango Accordion || 32. Guitar Harmonics|-! Bass !! Strings !! Ensemble !! Brass|-| 33. Acoustic Bass || 41. Violin || 49. String Ensemble 1 || 57. Trumpet|-| 34. Electric Bass (finger) || 42. Viola || 50. String Ensemble 2 || 58. Trombone|-| 35. Electric Bass (pick) || 43. Cello || 51. Synth Strings 1 || 59. Tuba|-| 36. Fretless Bass || 44. Contrabass || 52. Synth Strings 2 || 60. Muted Trumpet|-| 37. Slap Bass 1 || 45. Tremolo Strings || 53. Choir Aahs || 61. French Horn|-| 38. Slap Bass 2 || 46. Pizzicato Strings || 54. Voice Oohs || 62. Brass Section|-| 39. Synth Bass 1 || 47. Orchestral Harp || 55. Synth Voice || 63. Synth Brass 1|-| 40. Synth Bass 2 || 48. Timpani || 56. Orchestra Hit || 64. Synth Brass 2|-! Reed !! Pipe !! Synth Lead !! Synth|-| 65. Soprano Sax || 73. Piccolo || 81. Lead 1 (square) || 89. Pad 1 (new age)|-| 66. Alto Sax || 74. Flute || 82. Lead 2 (sawtooth) || 90. Pad 2 (warm)|-| 67. Tenor Sax || 75. Recorder || 83. Lead 3 (calliope) || 91. Pad 3 (polysynth)|-| 68. Baritone Sax || 76. Pan Flute || 84. Lead 4 (chiff) || 92. Pad 4 (choir)|-| 69. Oboe || 77. Blown Bottle || 85. Lead 5 (charang) || 93. Pad 5 (bowed)|-| 70. English Horn || 78. Shakuhachi || 86. Lead 6 (voice) || 94. Pad 6 (metallic)|-| 71. Bassoon || 79. Whistle || 87. Lead 7 (fifths) || 95. Pad 7 (halo)|-| 72. Clarinet || 80. Ocarina || 88. Lead 8 (bass+lead) || 96. Pad 8 (sweep)|-! Synth Effects !! Ethnic !! Percussive !! Sound Effects|-| 97. FX 1 (rain) || 105. Sitar || 113. Tinkle Bell || 121. Guitar Fret Noise|-| 98. FX 2 (soundtrack) || 106. Banjo || 114. Agogo || 122. Breath Noise|-| 99. FX 3 (crystal) || 107. Shamisen || 115. Steel Drums || 123. Seashore|-| 100. FX 4 (atmosphere) || 108. Koto || 116. Woodblock || 124. Bird Tweet|-| 101. FX 5 (brightness) || 109. Kalimba || 117. Taiko Drum || 125. Telephone Ring|-| 102. FX 6 (goblins) || 110. Bagpipe || 118. Melodic Tom || 126. Helicopter|-| 103. FX 7 (echoes) || 111. Fiddle || 119. Synth Drum || 127. Applause|-| 104. FX 8 (sci-fi) || 112. Shanai || 120. Reverse Cymbal || 128.Gunshot|}
This allowed musicians and composers to create music that would sound reasonably similar on any GM-compliant device, solving the patchwork compatibility issues of early MIDI systems.