Storage devices by Sai Akshitha

Secondary Storage devices Storage devices are used to store data

and instructions permanently. Secondary Storage devices are also called backing storage devices / external storage devices or auxiliary storage devices. Examples of storage devices include Hard Disk, CD and DVD etc.

Why are Secondary Storage Devices Used?

Primary memory (RAM) is volatile and temporary. When computer is switched off, all data in ram is erased.

Storage devices can store large amounts of data and instructions permanently whereas Primary memory has less capacity of storing data.

Hard Disk It consists of one or more metal plates. The plates

are fixed in the drive. Metal plates are coated with magnetic material to store data. A motor rotates disks. There is also an access arm and read / write heads to read and write data on disks. - The storage capacity of hard disk is much greater than floppy disk. - Now a days hard disks of size 40 GB, 80 GB or more are available. - Hard disk is covered in a hard jacket and there are less chances of disk damage due to dust and mishandling.- Now days Operating system and application programs are installed on hard disk.- Before using a magnetic disk we use operating system to format the disk. Operating system divides the disk into circles called tracks. Each track is divided into pie-shaped areas called sectors. Data is stored in sectors. Each sector can store 512 bytes.

CD-ROM CD-ROM stands for Compact

Disk-Read Only Memory. The data stored on Cd-Rom can only be read. It cannot be deleted or changed. It is a portable storage device. Data can be easily transferred by CD Rom from one computer to another. Commonly it can store 650 MB / 700 MB/ 750 MB data. It is used to store large amounts of data like Software or audio/video data.

DVD-RW DVD-RW

stands for Digital Video Disk Rewritable. User can write data on disk many times by erasing the old data.