Auxiliary Data Storage

Most digital computers store data not only in their RAM memory but also on auxiliary storage units. Here data and programs can be stored much like a file cabinet, not only for easy retrieval, but also to store data and programs that are too large to fit into the random-access memory at one time. These storage devices also offer a more permanent and secure method for storing programs and data compared to RAM memory, but much like RAM, offer a direct access to the data.

Floppy disks, hard disks, magnetic tape, and optical disks are examples of auxiliary storage devices. Floppy-disk drives (removable magnetic disks) can store a few million bytes of data on one disk and are used primarily in laptops and PCs. Hard disk drives are nonremovable magnetic media and are used with all types of computers. Compared to floppy disks, they access the data very quickly and can store significantly more information: from millions (megabytes) to billions (gigabytes) of bytes of data.

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. Most common are the read-only CD-ROM (or compact disk, read-only memory) disks on which manufacturers have pre-recorded the information onto a CD-ROM. Recordable CD-ROM disks, called WORM (write-once/read-many) are becoming an affordable alternative to tapes and hard disk, primarily for archival storage purposes. A single, small CD-ROM disk can hold more information than 1,000 floppy disks.

Contents

Prev. Page