At Brian Eno’s Wikipedia page:
The Microsoft Sound
In 1994, Microsoft corporation designers Mark Malamud and Erik Gavriluk approached Brian Eno to compose music for the Windows 95 project. The result was the six-second start-up music-sound of the Windows 95 operating system, The Microsoft Sound. In an interview with Joel Selvin in the San Francisco Chronicle he said:
The idea came up at the time when I was completely bereft of ideas. I’d been working on my own music for a while and was quite lost, actually. And I really appreciated someone coming along and saying, “Here’s a specific problem — solve it.”The thing from the agency said, “We want a piece of music that is inspiring, universal, blah-blah, da-da-da, optimistic, futuristic, sentimental, emotional,” this whole list of adjectives, and then at the bottom it said “and it must be 31/4 seconds long.”[† 1]I thought this was so funny and an amazing thought to actually try to make a little piece of music. It’s like making a tiny little jewel.In fact, I made 84 pieces. I got completely into this world of tiny, tiny little pieces of music. I was so sensitive to microseconds at the end of this that it really broke a logjam in my own work. Then when I’d finished that and I went back to working with pieces that were like three minutes long, it seemed like oceans of time.[27]
Eno shed further light on the composition of the sound on the BBC Radio 4 show The Museum of Curiosity, explaining that he created it using an Apple Mac computer, and stating “I wrote it on a Mac. I’ve never used a PC in my life; I don’t like them”.[28]