Secondary storage devices are used to store data semi-permanently as primary storage is volatile. Common secondary devices include floppy disks, hard disks, CDs/DVDs, pen drives, and magnetic tapes. Floppy disks use magnetic material coated plastic disks to store data in tracks and sectors, allowing direct access. Hard disks have multiple rigid platters that spin rapidly, containing data on both sides. Data is read and written by heads positioned very close to surfaces. Pen drives use flash memory and a USB interface for portable storage. DVDs can store more data than CDs due to higher density encoding and multilayer capabilities.

1. I.T. for Management
Chapter 4
Secondary Storage Devices

2. Secondary Storage Devices
• Most business information and particularly
transactions require semi permanent
storage
• The primary storage is Volatile in nature
• I.e all information is lost when power is
switched off
• Hence the need of secondary devices

3. Secondary Storage Devices
• Some of commonly used secondary
devices
– Floppy Disks & drive
– Hard disks
– CD/DVD Drive
– Pen drive
– Magnetic tapes

4. Secondary Storage Devices
Floppy Disks
The first floppy diskettes were introduced in the
year 1971
The floppy disk is packaged in a 8 inch square
soft plastic envelope
They had a capacity of 1 M.B
Later in 1976 5.25 inch diskettes were
introduced
………Cont.

5. Secondary Storage Devices
Floppy Disks
Basically, a floppy disk drive reads and
writes data to a small, circular piece of
metal-coated plastic similar to audio
cassette tape.
In this article, you will learn more about
what is inside a floppy disk drive and how
it works.
You will also find out some cool facts about
FDD’ s.
…. cont

6. Secondary Storage Devices
Floppy Disks
Parts of a Floppy Disk Drive
Floppy Disk Drive Terminology
• Floppy disk - Also called diskette. The common
size is 3.5 inches.
• Floppy disk drive - The electromechanical
device that reads and writes floppy disks.
• Track - Concentric ring of data on a side of a
disk.
• Sector - A subset of a track, similar to wedge or a
slice of pie.
The Disk
floppy disk is a lot like a cassette tape:
•

7. Secondary Storage Devices
Floppy Disks
Parts of a Floppy Disk Drive
• Both use a thin plastic base material coated with iron
oxide. This oxide is a ferromagnetic material, meaning
that if you expose it to a magnetic field it is permanently
magnetized by the field.
• Both can record information instantly.
• Both can be erased and reused many times.
• Both are very inexpensive and easy to use.

8. Secondary Storage Devices
Floppy Disks
Parts of a Floppy Disk Drive
If you have ever used an audio cassette, you know that it
has one big disadvantage -- it is a sequential device.
The tape has a beginning and an end, and to move the
tape to another song later in the sequence of songs on
the tape you have to use the fast forward and rewind
buttons to find the start of the song, since the tape heads
are stationary.
For a long audio cassette tape it can take a minute or two
to rewind the whole tape, making it hard to find a song in
the middle of the tape.
•

9. Secondary Storage Devices
Floppy Disks
• A floppy disk, like a cassette tape, is made from a thin
piece of plastic coated with a magnetic material on both
sides. However, it is shaped like a disk rather than a long
thin ribbon. The tracks are arranged in concentric rings
so that the software can jump from "file 1" to "file 19"
without having to fast forward through files 2-18. The
diskette spins like a record and the heads move to the
correct track, providing what is known as direct access
storage.
In the illustration , you can see how the disk is divided into tracks
(brown) and sectors (yellow).

10. Secondary Storage Devices
Floppy Drive
• The Drive
The major parts of a FDD include: Read/Write
Heads: Located on both sides of a diskette, they
move together on the same assembly. The
heads are not directly opposite each other in an
effort to prevent interaction between write
operations on each of the two media surfaces.
The same head is used for reading and writing,
while a second, wider head is used for erasing a
track just prior to it being written.

11. Secondary Storage Devices
Floppy Drive
• This allows the data to be written on a wider
"clean slate," without interfering with the analog
data on an adjacent track.
• Drive Motor: A very small spindle motor
engages the metal hub at the center of the
diskette, spinning it at either 300 or 360 rotations
per minute (RPM).
• Stepper Motor: This motor makes a precise
number of stepped revolutions to move the
read/write head assembly to the proper track
position. The read/write head assembly is
fastened to the stepper motor shaft.

12. Secondary Storage Devices
Floppy Drive
• Mechanical Frame: A system of levers that opens the
little protective window on the diskette to allow the
read/write heads to touch the dual-sided diskette media.
An external button allows the diskette to be ejected, at
which point the spring-loaded protective window on the
diskette closes.
• Circuit Board: Contains all of the electronics to handle
the data read from or written to the diskette. It also
controls the stepper-motor control circuits used to move
the read/write heads to each track, as well as the
movement of the read/write heads toward the diskette
surface.

13. Secondary Storage Devices
Floppy Drive
• The read/write heads do not touch the diskette media
when the heads are traveling between tracks. Electronic
optics check for the presence of an opening in the lower
corner of a 3.5-inch diskette (or a notch in the side of a
5.25-inch diskette) to see if the user wants to prevent
data from being written on it.

14. Secondary Storage Devices
Floppy Drive
Merits:
•In a floppy disk the files can be arranged Sequentially
• or in a random manner
The floppies being Removable makes it very easy to
transport
Requests for information can be answered quickly and at
random
De Merits :
The Floppy disks tend to get corrupted very easily because
of which of these factors
Floppy have lesser storage space
They are sources of virus

15. Secondary Storage Devices
Hard Disk Drive
• IBM developed the idea of the Winchester or the
hard disk
The hard disks are enclosed in a hermetically
enclosed container
Capacities of the order of 20 GB,40 GB,80 GB
are typical

16. Secondary Storage Devices
Hard Disk Drive
• How hard disk works:
A hard disk works on the same principle of Floppy drive
The entire assembly is permanently installed in the pc
The hard disk has one or more platter(disks) each with both
sides which are recordable
All platters rotate on a central spindle at continuous speed
are of the order of 7500 rpm
Several read write heads are position on top of each
rotating surface
When the hard disk drive receives the instruction to read or
write ,it uses the available data to locate the correct
surface track & sector & reads or writes on it

17. Secondary Storage Devices
Hard Disk Drive
• How hard disk works:
Hard disk is fast since it has to at most wait for the
correct track or sector to come below read or
write track,unlike floppy drive where the drive
works in addition to searching for track
Response time is of the order of 20 to 25
Millisecond is common

18. Secondary Storage Devices
Hard Disk Drive
• Here is a typical hard-disk drive:
Front side

19. Secondary Storage Devices
Hard Disk Drive
• Here is a typical hard-disk drive:
Backside

20. Secondary Storage Devices
Hard Disk Drive
In order to increase the amount of information the drive can store, most
hard disks have multiple platters. This drive has three platters and six
read/write heads:
Many drives use a "voice coil"
approach -- the same technique used
to move the cone of a speaker on your
stereo is used to move the arm.

21. Secondary Storage Devices
Hard Disk Drive
• Merits:
– Hard drive provides on line information & very
fast.
– Data access randomly & not sequentially
– Extra hard disk can be added increasing
storage capacity
– Hard disks are hermetically sealed reducing
chances of damage

22. Secondary Storage Devices
Pen Drive
What is pen drive
A pen drive is a small removable Flash memory drive
usually connected to the USB port
It provides storage ranging from 16 MB to several Giga
bytes
Data can be stored as long as it is needed
It is plug & play device
OS Xp automatically senses pen drive when inserted to
USB port
Typical dimensions are 77*25*9 mm

23. Secondary Storage Devices
Pen Drive(Inside)
Internals of a typical flash drive
(Saitek brand USB1.1 pictured)
1
USB connector
2 USB mass storage controller
device
3 Test points
4 Flash memory chip
5
Crystal oscillator
6
LED
7
Write-protect switch
8 Space for second flash memory
chip

24. Secondary Storage Devices
Pen Drive
• Merits:
– Massive storage capacity
– Portable & compact
– Solid state(no moving parts) hence less chance of
corruption
– USB compliant making easy to connect externally
– Does not require external power source
– Low cost (Rs 800-1000)

25. Secondary Storage Devices
DVD
• DVDs are of the same diameter and thickness as
CDs, and they are made using some of the same
materials and manufacturing methods. Like a CD,
the data on a DVD is encoded in the form of small
pits and bumps in the track of the disc.
• A DVD is composed of several layers of plastic,
totaling about 1.2 millimeters thick. Each layer is
created by injection molding polycarbonate plastic.
This process forms a disc that has microscopic
bumps arranged as a single, continuous and
extremely long spiral track of data.

26. Secondary Storage Devices
DVD
• Once the clear pieces of polycarbonate are formed, a
thin reflective layer is sputtered onto the disc, covering
the bumps. Aluminum is used behind the inner layers,
but a semi-reflective gold layer is used for the outer
layers, allowing the laser to focus through the outer and
onto the inner layers.
• After all of the layers are made, each one is coated with
lacquer, squeezed together and cured under infrared
light. For single-sided discs, the label is silk-screened
onto the non readable side. Double-sided discs are
printed only on the non readable area near the hole in
the middle. Cross sections of the various types of
completed DVDs (not to scale) look like this:

27. Secondary Storage Devices
DVD
DVD formats

28. Secondary Storage Devices
How DVD works
• Each writable layer of a DVD has a spiral
track of data. On single-layer DVD's, the
track always circles from the inside of the
disc to the outside. That the spiral track
starts at the center means that a single-
layer DVD can be smaller than 12
centimeters if desired.
• What the image to the right cannot impress
upon you is how incredibly tiny the data
track is -- just 740 nanometers separate one
track from the next (a nanometer is a
billionth of a meter). And the elongated
bumps that make up the track are each 320
nanometers wide, a minimum of 400
nanometers long and 120 nanometers high.
The following figure illustrates looking
through the polycarbonate layer at the
bumps.

29. Secondary Storage Devices
Data storage DVD/CD
• DVDs can store more data than CDs for a few reasons:
• Higher-density data storage
• Less overhead, more area
• Multi-layer storage
• Higher Density Data Storage
Single-sided, single-layer DVDs can store about seven times more data than
CDs. A large part of this increase comes from the pits and tracks being smaller
on DVDs.
• Specification CD DVD
• Track Pitch
1600 nanometers 740 nanometers
• Minimum Pit Length
(single-layer DVD) 830 nanometers 400 nanometers
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• Minimum Pit Length
(double-layer DVD) 830 nanometers 440 nanometers

30. Secondary Storage Devices
DVD
• Merits
• Superior quality
• Interactivity
• Flexibility
• Durability
• Low cost
• Compatibility
• Can handle all kinds of data including sound
& multimedia files
• Many drives allow read/write of both CDS &
DVD

31. I.T. for Management
End of Chapter 4