The document provides an overview of various types of computer storage devices, categorizing them into primary, secondary, tertiary, and offline storage. It details the characteristics, functions, and examples of each type, including RAM, ROM, hard disks, and cloud storage solutions. The information emphasizes the importance of storage devices in computer systems and their respective roles in data management.

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Secondary
Storage Devices

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STORAGE DEVICES
1. Computer Data Storage
2. Types of Storage
3. Other Examples of Storage Device

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Storage Devices
• A storage device is used in the computers to store
the data.
• Provides one of the core functions of the
modern
computer.

4. CSCA0101 Computing Basics
Types of Storage
There are four type of storage:
• Primary Storage
• Secondary Storage
• Tertiary Storage
• Off-line Storage
4

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Primary Storage
• Also known as main memory.
• Main memory is directly or indirectly
connected to the central processing unit via
a memory bus.
• The
CPU
continuously reads instructions stored
there and executes them as required.
• Example:
– RAM
– ROM
– Cache

6.  Every computer has a temporary storage built into
the computer hardware
 It stores instructions and data of a program mainly
when the program is being executed by the CPU.
 This temporary storage is known as main memory,
primary storage, or simply memory.
 Physically, it consists of some chips either on the
motherboard or on a small circuit board attached to
the motherboard of a computer
 It has random access property.
 It is volatile.
MAIN MEMORY

7. Property Desirable
Primary
storage
Secondary
storage
Storage
capacity
Large storage capacity Small Large
Access Time Fast access time Fast Slow
Cost per bit of
storage
Lower cost per bit High Low
Volatility Non-volatile Volatile Non-volatile
Access Random access
Random
access
Pseudo-
random
access or
sequential
access
STORAGE EVALUATION CRITERIA

8. Addresses of
a memory
The words
of a memory
(total N
words)
0
1
2
3
4
5
N-2
N-1
Bit 1 Bit
2
MAIN MEMORY ORGANIZATION
Each word
contains the same
number of bits =
word length
(Continued on
next slide)

9. MAIN MEMORY ORGANIZATION
 Machines having smaller word-length are
slower in operation than machines having larger word-
length
 A write to a memory location is destructive to its previous
contents
 A read from a memory location is non-destructive to its
previous contents

10. 0501
0502
0503
Word
B O M B A Y
D E L H I
1024
 Storage space is always allocated in multiples of word-length
 Faster in speed of calculation than variable word-length memory
 Normally used in large scientific computers for gaining speed of
calculation
FIXED WORD-LENGTH MEMORY
Address
Numbers

11. B
O
M
B
A
Y
0025
0026
0027
0028
0029
0030
0031
4096
D
E
L
H
I
0051
0052
0053
0054
0055
0056
4096
 Each memory location
can store only a
single character
 Slower in speed of
calculation than fixed
world-length
memory
 Used in small business
computers for
optimizing the use of
storage space
Note: With memory becoming cheaper and larger day-by-day, most
modern computers employ fixed-word-length memory organization
VARIABLE WORD-LENGTH MEMORY
Address
Numbers
Address
Numbers

12.  Memory capacity of a computer is equal to the number
of bytes that can be stored in its primary storage
 Its units are:
Kilobytes (KB) : 1024 (210) bytes
Megabytes (MB) : 1,048,576 (220)
bytes
Gigabytes (GB) : 1,073,741824 (230)
bytes
MEMORY CAPACITY

13.  Primary storage of a computer is often referred to as RAM
because of its random access capability
 RAM chips are volatile memory
 A computer’s motherboard is designed in a manner that
the memory capacity can be enhanced by adding more
memory chips
 The additional RAM chips, which plug into special sockets
on the motherboard, are known as single-in-line memory
modules (SIMMs)
 There are two types of RAM:
 DRAM (Dynamic Random Access Memory)
 SRAM (Static Random Access Memory)
RANDOM ACCESS MEMORY (RAM)

14. RAM

15.  ROM a non-volatile memory chip
 Data stored in a ROM can only be read and used – they
cannot be changed
 ROMs are mainly used to store programs and data, which
do not change and are frequently used. For example,
system boot program
READ ONLY MEMORY (ROM)

16. Type Usage
Manufacturer-
programmed ROM
Data is burnt by the
manufacturer of the electronic
equipment in which it is used.
User-programmed ROM
or
Programmable
ROM (PROM)
The user can load and store
“read-only” programs and data
in it
Erasable PROM (EPROM)
The user can erase
information stored in it and
the chip can be
reprogrammed to store new
information
TYPES OF ROMS

17. Type Usage
Ultra Violet
EPROM
(UVEPROM)
A type of EPROM chip in which
the stored information is erased
by exposing the chip for some
time to ultra-violet light
Electrically
EPROM
(EEPROM)
or
Flash memory
A type of EPROM chip in which
the stored information is erased
by using high voltage electric
pulses
TYPES OF ROMS
(Continued from previous slide..)

18.  It is commonly used for minimizing the memory-
processor speed mismatch.
 It is an extremely fast, small memory between CPU
and main memory whose access time is closer to the
processing speed of the CPU.
 It is used to temporarily store very active data and
instructions during processing.
Cache is pronounced as “cash”
CACHE MEMORY

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Secondary Storage
• It is not directly accessible by the CPU.
• Computer usually uses its input/output channels to
access secondary storage and transfers the desired
data using intermediate area in primary storage.
• Example:
– Hard disk

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Secondary Storage
Hard Disk
• The hard disk drive is the main, and usually largest,
data storage device in a computer.
• It can store anywhere from 160 gigabytes
to 2
terabytes.
• Hard disk speed is the speed at which content can
be read and written on a hard disk.
• A hard disk unit comes with a set rotation
speed varying from 4500 to 7200 rpm.
• Disk access time is measured in milliseconds.

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Secondary Storage
Hard Disk
Internal Hard disk External Hard disk

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Secondary Storage
Hard Disk
Internal Hard disk External Hard disk
Portability No Yes
Price Less expensive More expensive
Speed Fast Slow
Size Big Small

24.  Commonly used direct-access secondary storage device.
 Physically, a magnetic disk is a thin, circular
plate/platter made of metal or plastic that is usually
coated on both sides with a magnetizable recording
material such as iron-oxide
 Data are recorded on the disk in the form of tiny
invisible magnetized and non-magnetized spots
(representing 1s and 0s) on the coated surfaces of the
disk
 The disk is stored in a specially designed protective
envelope or cartridge, or several of them are stacked
together in a sealed, contamination-free container
HARDDISK - BASICS

25. Track
199
200
Tracks
Track 000
… …
 A disk’s surface is divided into
a number of invisible
concentric circles called tracks
 The tracks are
numbered consecutively from
outermost
to innermost starting
from zero
 The number of tracks on
a disk may be as few as
40 on
small, low-capacity disks, to
several thousand on large,
high-capacity disks
MAGNETIC DISK – STORAGE ORGANIZATION
ILLUSTRATES THE CONCEPT OF TRACKS

26. Illustrates Grouping of Tracks and Use of Different
Number of Sectors in Tracks of Different Groups for
Increased Storage Capacity
 Innermost
group
of
tracks has 8 sectors/track
 Next
groups
of
tracks
MAGNETIC DISK – STORAGE ORGANIZATION

27.  Disk address represents the physical location of the
record on the disk
 It is comprised of the sector number, track number,
and surface number (when double-sided disks are
used)
 This scheme is called the CHS addressing or Cylinder-
Head-Sector addressing. The same is also referred to
as disk geometry
MAGNETIC DISK – DISK ADDRESS OR ADDRESS
OF A RECORD ON A DISK

28. Central shaft
Upper surface
not used
Surface - 0
Surface - 1
Surface - 2
Surface - 3
Lower surface
not used
Surface - 4
Surface - 5
Cylinder
Access arms
assembly
Direction of
movement of
access arms
assembly
Read/Write head
MAGNETIC DISK – STORAGE ORGANIZATION
(ILLUSTRATES THE CONCEPT OF CYLINDER)
A set of corresponding
No. of disk platters = 4, No. of usable surfaces = 6.
tracks on all the 6 surfaces is called a cylinder.

29. Storage capacity of a disk system = Number of recording surfaces
 Number of tracks per surface
 Number of sectors per track
 Number of bytes per sector
MAGNETIC DISK – STORAGE CAPACITY
A 2.5 inch diameter disk plate has 4 plates , 512 bytes per sector , 8
sectors , 200 tracks per surface. What is the capacity of the disk in
terms of bytes ?
Number of recording surfaces = (4x2) -2
= 6
Storage capacity of a disk system= 6*x200x8x512 bytes
= 4915200 bytes
Each plate contain 2 surfaces except
the top most and bottom most all
disk contain data

30. HOME TASK
A 2.5 inch diameter disk plate has 6 plates , 512 bytes per sector ,
256 sectors , 5268 tracks per surface. What is the capacity of the
disk in terms of Giga bytes ?
Ans: 6.43 GB

31. Central shaft
One read/write
head per surface
Direction of
movement of
access arms
assembly
Access arms
assembly
Vertical cross section of a disk system. There is one read/write head per
recording surface
MAGNETIC DISK PACK – ACCESS
MECHANISM

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Tertiary Storage
• The main objective of the tertiary storage level is to
provide huge storage capacity at low cost.
• These storage devices are composed of fixed
storage drives and removable media units.
• The storage drives are fixed to the computer system.

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Tertiary Storage
• Examples:
– Magnetic Tape
– Optical Disc

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Tertiary Storage
Magnetic Tape
• A magnetically coated
plastic on which data
strip of
can
be
encoded.
• Tapes for computers are similar to
tapes used to store music.
• Tape is much less expensive than
other storage mediums but
commonly a much slower solution
that is commonly used for backup.

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Tertiary Storage
Optical Disc
• Optical disc is any storage media that holds content
in digital format and is read using a laser assembly
is considered optical media.
• The most common types of optical media are
– Blu-ray (BD)
– Compact Disc (CD)
– Digital Versatile Disc (DVD)

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Tertiary Storage
Optical Disc
CD DVD BD
Capacity 700MB 4.7GB – 17GB 50GB
Read/Write
Speed
1200KB/s 10.5MB/s 36MB/s
Example • CD-ROM,
• CD-R
• CD-RW
• DVD-ROM
• DVD+R/RW
• DVD-R/RW
• DVD-RAM
• BD-R
• BD-RE

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Off-line Storage
• Also known as disconnected storage or
removable storage.
• Is a computer data storage on a medium or a
device that is not under the control of a
processing unit.
37
• It
must
be inserted or connected by a human
operator before a computer can access it again.

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Off-line Storage
• Examples:
– Floppy Disk
– Zip diskette
– USB Flash drive
– Memory card

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Off-line Storage
Floppy Disk
• A soft magnetic disk.
• Floppy disks are portable.
• Floppy disks are slower to access than hard disks
and have less storage capacity, but they are much
less expensive.
• Can store data up to 1.44MB.
• Two common sizes: 5 ¼” and 3 ½”.

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Off-line Storage
Floppy Disk
5 ¼ inch Floppy Disk 3 ½ inch Floppy Disk

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Off-line Storage
Zip Diskette
• Hardware
developed
functions like a
data
storage by
Iomega
Standard
device
that
1.44"
floppy drive.
• Capable to hold up to 100 MB of
data or 250 MB of data on new
drives.
• Now
it
users
needed
less popular as
larger storage
capabilities.

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Off-line Storage
USB Flash Drive
• A small, portable flash memory
card that plugs
USB
a portable
into
a
port and
hard
computer’s
functions
as drive.
• Flash
drives
are available in
sizes such as 512MB, 1GB,
8GB,16GB, 32GB, 64GB and in
more capacity is avalible.USB is
an easy way to transfer and
store information.

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Off-line Storage
Memory Card
• An electronic flash memory storage disk commonly
used in consumer electronic devices such as digital
cameras, MP3 players, mobile phones, and other
small portable devices.
• Memory cards are usually read by connecting the
device containing the card to your computer, or by
using a USB card reader.

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Off-line Storage
Memory Card
Secure Digital card (SD) MiniSD Compact Flash Memory Stick
MultiMedia card XD-Picture card Memory card reader

45. •Cloud storage means "the storage of data online
in the cloud," wherein a data is stored in and
accessible from multiple distributed and
connected resources that comprise a cloud.
• Cloud storage can provide the benefits of
greater accessibility and reliability; rapid
deployment; strong protection for data backup,
archival and disaster recovery purposes.
Cloud Storage

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Other Example of Storage Devices
Cloud Storage
• Examples:
– Google Drive
– Flickr
– Microsoft Sky Drive