FamousMac Startup ChordApple Macintosh startup chime (1998 to 2016, back in 2020 a semitone lower), 1998 · Jim Reekes (sound designer, Apple); the 1998 version is his 1993 Quadra 840AV 'bong' pitch-shifted
The sound every Mac made when it was switched on
The warm 'bong' you heard every time a Mac was switched on from 1998 to 2016 is one big F sharp major chord. Jim Reekes stacked the notes like the natural overtones of a string: the root, the fifth, the root again and the major third on top. Apple even trademarked it, describing it as an F sharp major chord about a third of a semitone flat. Since macOS Big Sur in 2020 it plays a semitone lower, as F major.
Also called Mac startup chime, Mac bong, Apple startup chord
Sources: Macintosh startup (Wikipedia) · USPTO registration 4257783 (serial 85663397) via Justia · Apple's Mac startup chime now a registered trademark (Engadget, 2012) · The real reason that familiar Apple Mac chime is off key (Popular Science)