In digital computers , a physical device used to store such information as data or programs on a temporary or permanent basis.
Most digital computer systems have two types of memory, the main memory and one or more auxiliary storage units. In most cases, the main memory is a high-speed RAM . Auxiliary storage units include hard disks , floppy disks , and magnetic tape drives. Besides main and auxiliary memories, other forms of memory include ROM and optical storage media such as videodiscs and compact discs (see CD-ROM ).