Various secondary storage devices are classified into two categories
1. Detachable storage devices
2. Fixed storage devices
Detachable storage devices can be easily removed and can be inserted latter when needed. Some examples of detachable storage devices are Floppy disk, CD, DVD etc. Floppy disk is magnetic storage device where data is stored in concentric tracks of magnetic material in a plastic disk. They are used to store small amount of data (upto 1.44 MB). They can be easily inserted and can be easily removed.
Another storage device in CD (Compact Disk) and DVD (Digital Video Disk). They can be used to store large volume of data. A typical CD can store 700 Megabyte data and a DVD can store 8 Giga bytes to 16 Giga Byte data. They are used to store audio and video data as well as general data. Tapes are also detachable storage devices. They are basically sequential storage devices. They can be used for storing backup data and for on-line recording of transactions for future reference or for transaction processing system. They have magnetic based read/write mechanism.
One of the most popular secondary storage device is hard disk. Hard disk contains a stack of platters in which data is stored in concentric circular tracks. They are used in almost every computer. They are used to store the operating systems and files that are frequently used. Hard disks are not generally removed from computer. Currently small hard disks of 160 Giga bytes that can be externally connected through USB ports are available.
Another secondary memory device that is gaining popularity is pen drives. They are basically EPROM (Erasable and Programmable Read Only Memory) based memory. They are also called flash memory. They can be connected through the USB port of computer and can store upto 8 GB of data. They can be easily detached and carried in pocket. They can be used to store any type of data.
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