The document discusses different types of secondary storage devices. It describes sequential access devices like magnetic tapes that read and write data sequentially. It also describes direct access devices like hard disks that allow random access to stored data. Hard disks, floppy disks, disk packs, and zip disks are examples of magnetic disks. Optical disks like CDs, DVDs, and Blu-ray disks are also covered. Each type of secondary storage device has advantages and limitations in terms of storage capacity, access speed, portability and reusability.

1. Secondary Storage
Devices

2. CONTENTS
 Storage Devices
 Secondary Storage
Devices
 Classification of
Secondary Storage
Devices
 Sequential Access
Devices :
• Magnetic Tape

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.
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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.
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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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