This is technically correct but...what can happens to me if i start a song with exactly the same chord and frequencies ( the same synth)? Maybe nothing will happens to me (because i'm like a flea), but what if lady gaga, or U2, or other "big" musician do it? Well, also if a patent is different from copyright....surely in that case the Apple lawyers will start something! This is the money law!
That's not how trademark law works.
If anyone - big or small - produces a computer operating system with a startup sound sufficiently close the trademarked sound, it is the responsibility of Apple to enforce their trademark (first by requesting that the infringing sound is altered/removed and then through legal procedure to effect the same outcome).
If Lady Gaga produces a song composed entirely of the exact same chime, Apple can't and won't do anything about it - the general public isn't going to mistake a song on the radio for OSX. These are not even vaguely related things.
Copyright is a different story. If you own the copyright to a
progression of chords (a single chord chime is not enough to warrant protection AFAIK), then yes, you can
choose to enforce that copyright if another artist reuses your progression in their work (without permission).
This happens reasonably often too - Men at Work were successfully sued a few years ago by the owner of a folk song, because a progression from that folk song is played (in the background) throughout
Land Down Under.
Apple does not have copyright for their chime. They can't enforce the
trademark that they have except against those who would use it to identify a different business in the same industry (for eg. it prevents Microsoft from playing that chime on startup, and probably elsewhere, in their operating systems).
Just for the sake of clarity:
Copyright
The legal concept recognizing the creator as the owner of their work. You don't need to do anything to have copyright of your creation - it automatically applies (you don't even need to put the little (C) symbol and the date with your name, but it's not a bad idea to do so anyway).
You can choose to do what you like with your copyright - if people are infringing it, it's up to you whether or not you want to enforce it, and failing to do so does not alter your chances of successfully enforcing it in the future.
Copyright (traditionally) lasts a limited time. The US has been extending it an awful lot in the last 30 years or so.
OSX chime: Copyright does not apply in this case - a single chord chime does not qualify for copyright.
Patent
A patent is a protection for the creator of an invention. The patent gives the inventor sole rights to sell the invention for a limited time (usually ~20 years or fewer). The upshot is that if something is patented, its design/creation method becomes accessible to the public. After the exclusive period is over, competitors can begin making and selling their own copies.
OSX chime: A patent does not apply in this case - Apple hasn't invented anything new. Patent rules can be kind of esoteric, but it's fair to say that a chime is not an invention, and they aren't trying to sell the chime itself in any case.
Trademark
A trademark protects a particular sign or indication of a business, in order to prevent competitors from using those same marks to identify their own business. In short, if Dell began slapping an Apple logo on their pre-built machines, there'd probably be some confusion in the market and people would buy a Dell, thinking they were getting a Mac.
You can trademark stuff that simply could never be copyrighted - the word "Apple" for example is a registered trademark of Apple Inc.
Note that even though they've trademarked a single, extremely common word, that doesn't prevent grocers from selling apples.
What it does mean that Asus can't release the "Asus Apple Notebook" or something similar.
It's worth noting that if Apple
didn't enforce their trademark (in this hypothetical scenario, by having Asus change the name), then they might well stand to lose their trademark. This is distinct from copyright, where the owner can enforce it or not, as they like, at any time.
