So you need to search by metadata–the extra information that defines the contents of a file. Specifically, you need a program that can matches songs with the same title and by the same artist (because Smash Mouth’s “I’m a Believer” is not a duplicate of the Monkees’ original.)

You’ll also have to remember that no list of duplicate songs generated by software will be perfect. A program may not realize that Beatles and The Beatles are the same group. Nor can it always differentiate between the original studio recording and the live concert version. (I’ve known Dead Heads with probably ten versions of “Brokedown Palace.”)

But the right program can give you reasonably accurate lists to work through. Here are three I can recommend:

iTunes: Well, no, I wouldn’t recommend you download and install iTunes just for this purpose, but if you’re already using it, you’ve got a pretty good search tool. Just select File • Show Duplicates. If you have the same song as an .mp3 and a .m4a, iTunes will list both, but it won’t find any .wma versions.

Lincoln Spector, PCWorld