cd-rom disks can hold quite large amounts of data.
they are usually read-only
you cannot change the information on them.
Magnetooptical disks are like CD-ROMs
you can write data on to them
They are removable and have large capacities
they are expensive and do not conform to a standard
they are not very common. Magnetic tape is cheap and has a large capacity.
it does not allow random access and drives are slow
it is only suitable for backups.