apple.jpgNEW YORK (AP) – Apple unveiled an Internet radio service called iTunes Radio on Monday and said the service will personalize listeners' music based on what they've listened to and what they've purchased on iTunes.

Apple said iTunes Radio will be available in the fall in the U.S. It will be free with advertisements included, although subscribers of Apple's iTunes Match music-storage service will get a commercial-free version of iTunes Radio. That service costs $25 a year.

In unveiling the long-expected service Monday at its Worldwide Developers Conference in San Francisco, Apple enters a crowded field of rivals. Google Inc. started an on-demand subscription music service called All Access last month. Other leading services include Spotify, Rhapsody and Pandora.

Apple was a pioneer of online music sales and is still a leader in that field, but streaming services such as Pandora and Spotify have emerged as popular alternatives to buying. Pandora relies on its users being connected to the Internet at all times and plays songs at random within certain genres for free.

As with Pandora, iTunes Radio will let people create stations based on specific songs, artists or genres. So users can put in a particular song, and the station will play songs like it. Apple did not provide details on how the other songs will be determined. Pandora uses a formula to analyze songs based on musical and other characteristics.

The service will also offer featured stations, which play songs that are the most-talked about on Twitter, for example.

The service integrates Apple's Siri virtual assistant so that users can get information by speaking questions such as "Who plays that song?'' Users can also tell Siri to skip songs, stop or pause playing. And they can ask to play more songs like the one currently playing.

Apple said iTunes Radio will be built into iOS 7, the new software for mobile devices coming this fall. It will also work with Apple's iTunes software on Mac and Windows computers.