Magnetic-tape storage devices are much like audiocassette tapes. These devices are usually used on main-frame computer systems to handle high volumes of data. Compared to disks, tape drives access data very slowly and only sequentially. Nowadays, the role of the tape drive is limited to backing up or duplicating the data in the hard disk drive to protect the system against loss of data during power failures or computer malfunctions. The capacity of these devices ranges from few megabytes to gigabytes.
Optical disks are non-magnetic auxiliary storage devices that resemble audio compact disks.
Unlike magnetic media, the data are encoded on a disk as a series of pits and lands that can be read by a laser. Current technology allows about 600 megabytes of information to be stored, including reference text, computer programs, pictures, sound, and simple motion pictures or animation. A single, small CD-ROM disk can hold more information than 1,000 floppy disks.