BOSTON -- Apple is introducing a new iTunes feature that gives customers credit toward purchases of full albums from which they have bought individual tracks.

The feature, called Complete My Album, will let customers who have already bought individual tracks for 99 cents per song have the total price paid for those tracks deducted if they buy the full album.

Typically, it costs less to buy a whole album on iTunes than it would to purchase each individual track on an album.

Whenever someone buys a song, the full album will appear on a personalized page for the new service.

The offer is good for the 180 days after the individual tracks are first purchased.

Apple says that iTunes has the world's largest music catalog, with more than 4 million songs, 350 television shows and 400 movies. It says it has sold more than 2 billion songs.

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