An optical disc is typically made in one session. The data on a single-session disc cannot be changed, and data can not be added to the disc. However, the Orange Book specifies a special format for recordable CDs: multi-session discs. This format allows you to use one disc for one or more additional recording sessions. After the initial data is burned into the disc, it is possible to add data during future sessions until the disc is full. Since you cannot change information on a recordable disc, a new session should contain a table of contents comprised of the old and the new information on the disc. The system that reads a multi-session disc needs to take this into account. It should not look for just any table of contents or directory of a CD-ROM disc; it should look for the last table of contents or directory. Because of this issue, many older CD-ROM drives cannot read multi-session discs.