A CD has an "index" area which contains track details; this is what is
read when you first stick an audio CD into a player. Photo-CDs have a
separate index area each time they are written (because it is impossible
to "update" the index area). A multisession drive is one that knows to
look for multiple index areas. The full details are contained in the
Philips/Sony/Kodak "Orange Book" standard for writable CDs.
