Between work, home, and the family network, not everyone spends time on just one computer these days. So Apple lets you play your Music Store songs on up to five computers at once: Macs, PCs, or any combination. You just need to type in your Apple user name and password on each computer. Each must make an Internet connection to relay the information back to Music Store headquarters.
You authorized your first machine when you signed up for an Apple Account for the iTunes store.
To authorize a song to play on another computer, follow these steps:
Find the song you want to transfer.
This step, of course, involves finding the song on your hard drive.
Method 2: Just drag the song you want out of the iTunes window and onto your desktop.
Copy the song to the second computer.
Copy the song file onto a CD or USB flash drive; email it to yourself; transfer it across the network; or whatever method you prefer for schlepping files from machine to machine.
Deposit the songs in the Home → Music → iTunes → iTunes Music folder on the Computer #2.
Bring the copied song into iTunes on the second computer.
To do that, you can either choose File → Add to Library (and then select and open them), or just drag their icons right into the iTunes window.
In your iTunes list, select a transferred song and click the Play button.
iTunes asks for your Apple Account user name and password.
Type your Apple ID and password, and click OK.
This second computer is now authorized to play that song—and any other songs you bought using the same Apple Account.
Although you may feel like AAC stands for Always Authorizing Computers, remember that this whole authorizing business is necessary only to play songs you’ve bought. To play songs you’ve ripped into AAC format from CDs, for example, or to play everyday MP3 files, you don’t have to authorize anything.
You won’t be able to play the purchased music on a sixth computer if you try to authorize it. When you connect to the authorization system over the Internet, it will see five other computers already on its list, and deny your request.
That’s a drag, but copy protection is copy protection—and it’s much better than rival music services, which permit you to play downloaded music only on three machines (just like iTunes did before 2004).
In any case, you have to deauthorize one of the other computers if you want to play the music on Number 6. To deauthorize a computer, choose Advance → Deauthorize Computer, and then type in your Apple Account user name and password. The updated information zips back to Apple over the Internet.