Secondary Storage

Secondary Memory:

Secondary Memory is computer storage area that is not accessed directly by the User. Auxiliary memory, also known as auxiliary storage, secondary storage secondary memory or external memory, is used to store a large amount of data at lesser cost. As soon as a computer starts, copy of all system software, including the operating system (OS) that is saved on Secondary storage is transferred to primary memory.  The amount of Secondary memory on a computer is tells you the amount of data you can store for later use.

·       The Secondary memory is the non-volatile memory. The non-volatile memory is the kind of the memory that retains data if there is no continue supply of electricity.

·       The secondary memory store data permanently.

·       The secondary memory has large capacity to store data (4GB to 500GB).

·       The secondary memory is a slow speed memory.

Types of Secondary Memory:

There are three types of Primary memory:

·        Optical disc: Its a storage medium from which data is read and to which it is written by lasers. Optical disks can store much more data—up to 6 gigabytes (6 billion bytes)—than most portable magnetic media, such as floppies. There are three basic types of optical disks: CD-ROM ( Read only ), WORM ( Write-Once Read-Many ) & EO (Erasable Optical disks).

·        Magnetic Disk: A magnetic disk is a circular plate constructed of metal or plastic coated with magnetized material. Both sides of the disk are used and several disks may be stacked on one spindle with read/write heads available on each surface. Bits are stored in magnetised surface in spots along concentric circles called tracks. Tracks are commonly divided into sections called sectors. Disk that are permanently attached and cannot removed by occasional user are called Hard disk. A disk drive with removable disks are called a floppy disks.

·        Magnetic tapes: A magnetic tape transport consists of electric, mechanical and electronic components to provide the parts and control mechanism for a magnetic tape unit. The tape itself is a strip of plastic coated with a magnetic recording medium. Bits are recorded as magnetic spots on tape along several tracks. Seven or Nine bits are recorded to form a character together with a parity bit R/W heads are mounted in each track so that data can be recorded and read as a sequence of characters.