STORAGE DEVICE OR SECONDARY MEMORY

Secondary Memory is the external memory of a computer. Secondary Memory is also called Auxiliary memory or device. Since the RAM is not permanent, a computer system requires secondary memory to hold data and programs permanently. The CPU can not directly access data and programs of secondary memory. They first need to transfer into RAM before being used. Most widely used secondary storage devices are magnetic tapes, magnetic disk (Hard disk, floppy disk), optical disk (CD, DVD) and flash drive. These devices store data, information and programs permanently in the form of binary digits till we don’t erase them.

a) Hard Disk
Hard Disk is present inside the system unit. Hard disk is the main secondary storage device that stores large amount of data permanently. Hard disk is also called fixed disk. Hard disk stores operating system software of a computer, data and other applications software. Hard disk consists of many metal disks or platters coated with magnetic material that store data in tracks, which is further divided into sectors. The various capacities of Hard disks are available in the market. Nowadays hard disk of 1TB (Tera Byte) is available in the market.

b) Floppy Disk
A floppy disk is a portable storage device that stores data permanently. The floppy disk drive is used to read and write data on a floppy disk. Floppy disk may be mini floppy disk or micro floppy disk. The storage capacity of a Micro Floppy disk is 1.44 MB (Mega Byte) and of a Mini floppy disk is 1.2 MB. Floppy disk gets damaged easily. So, nowadays it is not used. Floppy disk is a thin plastic disk coated with magnetic material for storage of data or information. Floppy disk has a hard outer covering. Floppy disk is inserted into the disk drive while saving information into it or copying files into it. Thus, the file can be transferred into other computer.

c) Compact Disk/DVD
Compact Disk/Digital Video Disk stores huge amount of data permanently. The Compact Disk Drive (CD-ROM) is required to read data from a compact disk. A CD-RW drive is used to write data on blank CDs and delete, modify or add data on an already written CD-RW (CD-Rewritable). DVD Drive (DVD-ROM) is required to read the data from DVD (Digital Versatile Disk). DVD Writer allows you to read as well as write data on DVDs. The capacity of a compact disk is 700MB and DVD is 7 GB. CD/DVD is portable disk that can be used for transferring data and programs from one computer to another computer. Since CDs and DVDs are reliable storage devices they are also used for keeping backup copy of data and programs.

d) Pen Drive
Pen drive is also called Flash Drive. Pen drive is a portable device used for transferring data and programs from a computer to another computer. You can use a pen drive to copy data, songs, games and programs from one computer to another computer. Different storage capacities of pen drives (256 MB to 16 GB) are available in the market.