Uses of storage devices
CD-ROM / DVD-ROM
These tend to be used to install software or store multimedia . They tend not to be used for backup as once they have been written they can not be changed.
Memory sticks / portable hard drives
These are used to back up data and transport files from one place to another. Hard drives found inside a PC is known as primary storage while portable hard drives are known as secondary storage.
Magnetic tape
These are commonly used to backup and archive large amounts of data. It is very common for magnetic tape to be used in companies.