The optical disks used in read-only compact disks (CD-ROM) or read-only
digital video disks (DVD-ROM) cannot be written, but are supplied with data
prerecorded. There are also “record-once” versions of compact disk (called
CD-R) and digital video disk (called DVD-R and DVD+R), which can be written
only once; such disks are also called write-once, read-many (WORM) disks.
There are also “multiple-write” versions of compact disk (called CD-RW) and
digital video disk (DVD-RW, DVD+RW, and DVD-RAM), which can be written
multiple times.
Optical disk jukebox systems contain a few drives and numerous disks
that can be loaded into one of the drives automatically (by a robot arm) on
demand.