Secondary storage devices

storage devices

1. Secondary Storage Devices

2. CONTENTS Storage Devices Secondary Storage Devices Classification of Secondary Storage Devices Sequential Access Devices : Magnetic Tape Direct Access Devices : Magnetic Disks Optical Disks

3. Storage Device A storage device is a hardware device designed to store information. Available in different form factors depending on the type of underlying device. There are two different types of storage devices: Primary and Secondary.

4. Secondary Storage Devices These usually have large storage capacity , and they store data permanently . They can be both internal and external to the computer, and they include the hard disk, compact disk drive and USB storage device .

5. Classification of commonly used secondary storage devices

6. Sequential Access Devices A storage technology that is read and written in a serial (one after the other) fashion. Magnetic tape is the common sequential access storage device. Magnetic Tape is an example. 1 2 3 4 5 6

7. Magnetic Tape It is a ¼ inch or ½ inch ribbon of plastic on which data is recorded. It reads ,writes and erases data on tapes. They are erasable , reusable and durable and made to store large quantities of data.

8. No direct access, but very fast sequential access. Resistant to different environmental conditions. Easy to transport , store ,cheaper than disk. Before it was widely used to store application data; nowadays it’s mostly used for backups or archives(tertiary storage). Characteristics

9. ADVANTAGES AND DISADVANTAGES Probably the cheapest form of storage per megabyte of storage. Can store large amount of data – up to 1 terabyte per tape cartridge. Can be set up to do the back up overnight or over the weekend. Serial access so can be quite slow to access data. Need a special piece of equipment to record and read the data on the tape. The data may be corrupted if the tape is placed near a strong magnetic field e.g. a large speaker or magnet.

10. USES Today, tape based systems are usually used for backup purpose only. Provides the most cost effective method of storing larger amounts of backup information. Reliable as long as the temperature is kept low and humidity conditions are kept right. Tapes are portable. Backups can be taken off-site for greater risk prevention.

11. Direct Access Devices A direct-access storage device store data in discrete locations with a unique address, such as hard disk drives, optical drives and most magnetic storage devices.  1 2 3 4 5 6

12. MAGNETIC DISK A magnetic disk is a storage device that uses magnetization process to write, rewrite and access data. Example of magnetic disks are zip disk, floppy disk and hard disk.

13. ADVANTAGEs Suitable for both on-line and off-line storage of data. More suitable than magnetic tapes for wider range of applications because they support the direct access of data. Direct access property enables them to be used simultaneously by multiple users as a shared device. Very large amount of data can be stored in a small storage space.

14. Due to their low cost and high data recording densities, the cost per bit of storage is low for magnetic disks. They are easy to handle and store, can be erased and reused many times. Compact in size and light in weight due to this they are easily portable from one place to another. Any information can be accessed in a few milliseconds because it is a direct access storage device.

15. Must be stored in dust free environment. Such as disk packs and Winchester disks are not easily portable like magnetic tapes. The cost of magnetic tapes are cheaper than magnetic disk. It is less efficient than magnetic tapes. More difficult to maintain the security of information stored on shared on-line secondary storage devices, as compared magnetic tapes or other types of magnetic disks. limitations

16. types FLOPPY DISK : Also known as floppies or diskettes. Two types : 5¼ inch and 3½ inch. Most popular and inexpensive. Vinyl jacket cover that gives handling protection. Flat piece of flexible plastic coated with magnetic oxide.

17. HARD DISK: Primary on-line secondary storage device for most computer systems today. Size varies from 1 to 14 inch in diameters. Depending on how they are packaged, they are of 3 types: Disk pack, Winchester disks and Zip disks.

18. Zip disk. Disk Pack. Winchester Disk.

19. USES As a backup device for off line storage of data. As a shared on-line secondary storage device. For applications that are based on some random data processing. Transferring of data from one computer to another which are not connected to each other.

20. optical DISK An optical disc is an electronic data storage medium that can be written to and read using a low-powered laser beam. Example of CD-ROM, WORM(CD-R), CD-RW, DVD.

21. Mass storage capacity (on the order of gigabytes) Mountable/ unmountable storage units. Low cost per bit of storage. Long media life. High data stability. ADVANTAGEs

22. limitations It is a read-only(permanent) storage medium. Data   once recorded, cannot be erased, and hence, the optical disks cannot be reused. The data access speed for optical disks is slower than magnetic disks. Optical disks require a more complicated drive mechanism than magnetic disks.

23. types CD-RW: Can be written to repeatedly, by deleting or overwriting old data to make room for new data up to 1,000 times. Now much less widely available than CD-R discs, which remain commonplace.

24. DVD: DVDs offer higher storage capacity than CD’s while having the same dimensions. Designed primarily to store and distribute movies.

25. CD-R CD-ROM

26. USES For distribution of electronic version of conference proceedings, journals, magazines, books, product and catalogs, etc. For distribution of new or upgraded versions of software products by software vendors. For storage and distribution of a wide variety of multimedia applications, such as video games. For archiving of data, which are not used frequently, but which may be used once in a while. WORM disks are often used by end-user companies to make permanent storage of their own proprietary information

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