Will iTunes copy twice if song is in multiple playlists?

"I believe that the playlist is just basically a list of songs and not the songs themselves so for example, a playlist will just contain a number/ID of what song to play and not the song itself.

You should be able to have many playlists with overlapping songs and only copy the music once."

"NOTE: This answer doesn't directly refer to iPods, but to mp3 players in general

On other mp3 players the playlist is held in a file with the m3u extension which looks like this:

#EXTM3U
#EXTINF:244, Eurythmics - English Summer
e:\chris\music\Eurythmics\In The Garden\01-English Summer.mp3
#EXTINF:239, Eurythmics - Belinda
e:\chris\music\Eurythmics\In The Garden\02-Belinda.mp3
...

The first line tells the system what sort of file it is.

Each track in the playlist is represented by a pair of lines. The first gives the length in seconds, the artist and the name of the track, the second gives the location of the file. So you can see that the file can be in multiple playlists without being copied to multiple locations.

I would expect the iPod playlist file to be organised on very similar lines."