The number of sessions a compact disk has refers to the number of different continuously-written chunks of data that are placed on the disk. Some newer CD formats however use more than one session, and are called multi-session drives. Using multiple sessions means that information can be written to the first part of the disk, and then later more information can be appended to it in the unused space left after the first session. Multi-session capabilities are provided by many newer drives, and are required for some of the fancier CD formats.
Some formats have versions that use single sessions or multiple sessions.
For this reason, support for multi-session has not traditionally been considered an essential feature, and the vast majority of legacy drives will not support it. The reason that specific support is required for multi-session disks is that standard disks have only a single place for storing the table of contents of the disk. This makes sense, because traditionally disks always had their entire contents recorded at once. Drives that support multi-session disks are programmed to seek out these multiple tables of contents that can occur in various places on the disk. This page has been served 11935 times.