iTunes is a digital media player application, introduced by Apple on January 10, 2001 at the Macworld Expo in San Francisco,[2] for playing and organizing digital music and video files. The program is also an interface to manage the contents on Apple's popular iPod digital media players as well as the recently introduced iPhone. Additionally, iTunes can connect to the iTunes Store (provided an internet connection is present) in order to purchase and download digital music, music videos, television shows, iPod games, audio books, various podcasts, feature length films, and ringtones.

iTunes is available as a free download for Mac OS X, Windows Vista, and Windows XP from Apple's website. It is also bundled with all Macs, and some HP and Dell computers. Older versions are available for Mac OS 9, OS X 10.0-10.2, and Windows 2000.

[edit] Features
Users are able to organize their music into playlists within one or more libraries, edit file information, record compact discs, copy files to a digital audio player, purchase music and videos through its built-in music store, download podcasts, back up songs onto a CD or DVD, run a visualize to display graphical effects in time to the music, and encode music into a number of different audio formats. There is also a large selection of internet radio stations from which to choose.

Playlists
In addition to static playlist support, iTunes supports 'Smart playlists'. Smart playlists are playlists that can be set to automatically update (live updating, like a database query) based on a customized list of selection criteria. Different criteria can be entered to control many aspects of the playlist.[3]

Playlists can also be published by a user of iTunes with his or her own preferences.

Playlists can be played randomly or sequentially. The "randomness" of the shuffle algorithm can be biased for or against playing multiple tracks from the same album or artists in sequence (a feature introduced in iTunes 5.0). Party Shuffle can also be biased towards selecting tracks with a higher star rating. With this bias enabled, each star rating increases the preference for that particular song about 4% over that of a one-star-less rated song. Unrated songs are the least likely to be played. Inter-star ratings are stored by iTunes, but only affect this feature in the range of zero to one star.

The Party Shuffle playlist is intended as a simple Ding aid.[4] By default, it selects tracks randomly from other playlists or the library; users can override the automatic selections by deleting tracks (iTunes will choose new ones to replace them) or by adding their own via drag-and-drop or contextual menu. This allows a mixture of both preselected and random tracks in the same meta-playlist. The playlist from which Party Shuffle draws can be changed on the fly; this will cause all randomly chosen tracks to disappear and be replaced.