Discuss about Various Secondary Storages Devices.

Semester:-1

Unit:-4

Discuss about Various Secondary Storages Devices ?

Ans:-
          When the computer is switched off, anything stored in the RAM is lost. To avoid this situation, magnetic disks are used to store data permanently. The data , on these disks, won't be affected when we turn off our computer.
a) Floppy Disk : 
                            A Floppy Disk is a reusable data storage device that is composed of a disk of thin, flexible ("Floppy" ) magnetic storage medium encased in a square or rectangular plastic shell. Also called a " diskette", the Floppy is a flexible circle of magnetic material similar to magnetic tape , except that both sides are used. The read/write head contact the surface through an opening in the plastic shell or envelope. Floppies rotate at 300 RPM, which is from 10 to 30 times slower than a hard disk. Floppy disks basically come in three sizes, they are 8 inches, 5 1/4 inch , and 3 1/2 inch .

b) Hard Disk :
                        A hard disk, is also a permanent storage , where we can store lot of information. Capacity of a hard disk is measured in megabytes ( MB), Gigabytes (GB) or Terabytes (TB) and they come in various different sizes. Usually every computer now a day comes with hard disk.

The information in hard disk is stored in circular magnetic disks called plates , in the form of program files and data files.
c) CD-ROM ( Compact disk-Read only memory) :
                  CD-ROM is also one of the commonly used secondary storage device. The main advantage of CD-ROM is, they can store large volumes of data I.e., 700 MB to 1.4 GB and also they are cheaper and easy to handle. It is made up small plastic disk, coated with aluminum or silver for magnetization. A layer or transparent plastic is further deposited on the disk . The data is recorded in spiral tracks and the data once recorded cannot be deleted or rewritten , but can be read any number of times .
               In this technology, a high power laser beam is used to record data by burning tiny pits in the surface of the hard plastic disk . To read the data, a low power laser beam is used to scan the disk surface. The data are stored in binary digits . When the laser beam reflect from the smooth surface of the disk it is interpreted as a 1 bit and when the beam enters the tiny pits it is interpreted as a 0 bit .
Advantages : 

• High Storage Capacity
• Easy to use in multimedia applications.
• Handled easily
• Can read / Rewrite using CD-RW's

Disadvantage: 

• CD Writing can be done carefully
• Should be kept free from dust and heat.

d) Magnetic Tape :
                                 Magnetic Tape is the oldest form of secondary storage device. It is one of the popular storage medium for storing large amount of sequential data . It is also used as a backup storage for data stored on on-line storage devices.
The magnetic tape medium is a plastic ribbon usually 1/2 inch or 1/4 inch wide and 50 to 2400 feet long. It is coated with a magnetizable recording material such as iron-oxide or chromium dioxide . Data are recorded on the tape in the form of tiny invisible magnetized and non-magnetize spots on the coated surface of the tape.
Advantages :

• Non-volatile Memory
• Voluminous data can be stored.

Disadvantages :

• Only sequential data processing
• Complex mechanism required.
• After few days the data can be mounted to tape , we need to recall the data to store it into hard disk as and when required .

Fig: Magnetic Tape