Interesting history of the Mac startup chime on Quora:
The Apple II made short beep in its boot sequence [1], a courtesy signal that sound was working. (Funny that similar “triple beep” sequences mark issues on boot [2].) Charlie Kellner wrote an algorithm to average adjacent 8-bit square waves for the tone used on the (original) Mac 128K [3].
The sound grew punchier, and by the Mac Classic/Mac II era, it was similar to a “tritone” sound (a music theory no-no). This annoyed Jim Reekes, who took over Sound Manager in 1990 [4]. He sought to use the improved sound cards for a cheerful “palate cleanser” sound, as the tritone wasn’t music to one’s ears during post-crash reboots. He snuck a “fat” C major chord backed with sonic textures into the ROM. The textural properties included stereo reverb, phaser, some sharp transients, and strings [5]. This chime was used through the mid-90s; starting in the Quadras, through the Performas.
The Power Macintosh 6100 (first PowerPC, 1994) used 12-string acoustic guitar harmonics designed by jazz guitarist Stanley Jordan [6]. It was short-lived, because the Power Macintosh 9500 (1995) returned to Reekes’s chime. (He has speculated that perhaps this was due to Jobs’s return, but that was late 1996.) It stayed more or less the same until the iMac G3 (1998), save for the Twentieth Anniversary Mac. It hasn’t changed since.
I liked the earlier chimes more than the recent ones.