Secondary storage organisation

Secondary storage is also known as secondary memory or auxiliary storage.

Secondary storage device are also useful in transferring data or program from one computer to another. They are also used as backup devices. The most common type of secondary storage devices are magnetic tapes, magnetic disk, floppy disk, hard disk, etc.

Classification of secondary storage device

     a.     SEQUENTIAL ACCESS:-         Sequential access is also called as serial access. Magnetic tape is common sequential access storage device.

     b.    RANDOM ACCESS: -    Random access is called as direct access. The example of random access media is hard disk, optical disk, zip disk, etc.

Types of secondary storage device:-

    1.   MAGNETIC TAPE: -

1.a. Half-inch magnetic tapes: - Its memory capacity is 60 MB to 400 MB.

1.b. Quarter-inch cartridge tape: - Its storage capacity is 40 MB to 5 GB. 

1.c. 8mm helical scan: - Its storage capacity is 2.5 MB to 15 GB. 

1.d. 4mm DAT(Digital Audio Tape): - Its storage capacity is 2 GB to 24 GB.

     2.   MAGNETIC DISK: -       Magnetic disks are the most popular direct access secondary storage device. Magnetic disks offer several advantages over magnetic tapes. Individual record can be accessed much faster.

2.1.         HARD DISK

2.1.a. Removable pack disk system: -     They are typically found in mainframe and minicomputer system. Removable pack disk system consists of hard disk placed into a pack unit that can be mounted or removed as a unit. A typically disk pack has 11 disk.

2.1.b. Winchester disk system: -     Winchester disk is also known as fixed hard disk system. They are typically used in microcomputer. Winchester disks are sealed units that cannot be removed from the disk drive.

2.2.         FLEXIBLE DISKS

2.2.a. Floppy disk: -     A floppy disk is a flat, circular piece of flexible plastic, coated with magnetic oxide and encased in a square plate. Floppy disks are portable. Floppy disks are slower to access and have less storage capacity.

     3.   OPTICAL DISK

a.      CD-ROM: -        Compact Disk Read only memory. CD-ROM is a type of optical disk capable of storing of large amount of data up to 1GB. The most common size is 630MB to 700MB. It is a read only storage medium. These CD-ROM are once recorded only and they cannot be erased and filled with new data.

b.     WROM Disk/CD-R Disk: -        WROM stands for write once read many. WROM disk look like standard CD-ROM disk but they are blank and encoded/write later by using CD-R drive. Like CD-ROM disk, once data has been written on the surface of a WROM disk it become permanent and can be read but never changed.

c.      Erasable/CD-RW Disk: -        CD-ROM enables to erase the previous content and write on it multiple times. Such disk uses metallic alloy layer. These disks just behave like floppy disk or hard disk.

d.     DVD: -       DVD stands for Digital versatile disk or Digital video disk. It is just similar to CD-ROM but its minimum storage capacity is 4.7GB and maximum up to 17GB. Its data transfer rate is from 600 KBPS to 1.3 MBPS.

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