Write about secondary storage devices of computers ?

In order to store all information permanently, the computer Secondary Memory devices are used. These secondary storage devices are used to store large files and data and then can be reloaded into the main memory, for processing. Once the files are saved into the computer, You can retrieve it, as and when required by the user. The Secondary storage devices has a large storage capacity and is cheaper than Primary storage. The Magnetic memories are used for secondary storage and thus, they are semi-conductor devices.

The Magnetic memories are divided into two categories. 

i) Carriable memories

Examples: Floppy disk, Compact disk, Magnetic disk

ii) Non–carriable memories .

Example: Hard disk 

The popular secondary storage devices are magnetic disk, magnetic tape and CD ROM.

MAGNETIC DISK: 

The Magnetic disks are made up of synthetic plastic material. The disk plotter is coated on both sides with magnetic material and both the surfaces can be used for storage. 

The magnetic disk provides direct access of data. 

The magnetic disks are divided into two types. 

i) Floppy disk

ii) Hard disk

1. FLOPPY DISK: - 

1. The floppy disk is flexible, low cost storage device. It is a circular thin plastic disk coated with magnetic material on the both sides. 

2. It is divided into tracks and sectors magnetically. When reading and writing is performed, the spindle holds the disk and rotates very fast. 

3. It is used to record and take the information from one computer to any other computer easily. 

4. It we don’t need the information stored in a floppy, we can delete the unwanted information and store some other information in its place. The limitation of floppy is that we can store only limited amount at data depending on the size of the Floppy. The floppy disks are available in two sizes. 

i) 51/4 inches (1.2 MB)

ii) 31/2 inches (1.44 MB)

2. HARD DISK:-

1. The hard disk contains a group of thin magnetic plates coated on both sides with magnetic material.

2. These disks are fixed to a spindle one below other 

3. The spindle is fixed to a metal to rotates the disk very fast (60 rotations per second)

4. It has a group of magnetic heads mounted on an arm. The main arm can move the head radically over the disk.

5. Each magnetic plate is logically divided into tracks. The track is a circular path to the disk. The set of concentrate tracks on all surfaces of the disks is called a cylinder. 

6. The track is further divided into sectors. The data is stored sector to sector. 

7. To axis the data from the disk, the specified cylinder number, surface numbers and sector number is read.

8. After giving the command to access the specified data, the time for the disk to access is called access time. 

9. Access time is the sum of seek time and latency time. The seek time is the time taken for the head to reach the specific cylinder. The latency time is the taken to reach the specific sector on the cylinder.

10. The storage capacity of Hard disk is 80GB to 500 G.B and even more.

3. MAGNETIC TAPES: -

1. Magnetic tape is a storage device. It used as back up storage. 

2. The advantage of magnetic tape is its low cost and large storage capacity. 

3. Its main disadvantage is that, it can store and execute the information sequentially. So the access time is very high.

4. The magnetic tape is made up of magnetic material. The standard type is ½ inch wide and has 9 tracks. It is created with iron oxide and has 9 tracks. It is created with iron oxide magnetic material. 

5. The newer ½ inch wide type contains 19 tracks and coated with chromium dioxide. 

6. The data is stored as records and group of records are called as a block. While storing, a gap is left between the blocks. It is called inter-record gap block. 

7. A set of blocks form a file. The tape contains file identification marks to recognize the beginning and ending of file.

4. COMPACT DISK( CD): -

1. Compact disk is the most existing development that has taken place in secondary storage in recent years. 

2. It is the latest technology with high capacity storage disk that work with laser.

3. It is the optical fibre disk having shine metal coating with 5¼ inches diameter.

4. The information is stored by creating pits on the surface of the disk with the laser beam while reading a disk, the head send pits and converts them into digital data.

5. If there is a pit it is one otherwise zero.

6. We can store different types of data such as audio, video, text files, animation, pictures and graphics on the disk.