Data on a Red Book audio compact disc is 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 on a disc. 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 previous sessions. The TOC written in the lead-in of the latest session is used to access the tracks.
Read more about this topic: Optical Disc Authoring