Session (CD)
Data on a compact disc
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...

 or a DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

 are laid out in sessions. Each session consists of a lead-in, containing the session's table of contents, the program area in which the individual tracks
Track (CD)
On an optical disc, a track or title is a subdivision of its content. Specifically, it is a consecutive set of sectors on the disc containing a block of data. One session may contain one or more tracks of the same or different types...

 are located, and the lead-out.

The number of tracks is limited to 99 in a session. The specifications require at least one track in each session. The tracks are located in the program area of the session.

In multisession discs, the lead-in areas contain addresses of the subsequent sessions. The TOC written in the lead-in of the latest session is used to access the tracks.
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