Data on a compact disc or a DVD 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 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.