Introduction to Computers - Manonmaniam Sundaranar University

Introduction to Computers - Manonmaniam Sundaranar University
Unit I: Introduction to Computers
Introduction to Computers: Introduction – Characteristics of computers- Evolution of
computers – Generation of computers – Based on purpose, Based on type of data handling
techniques, and according to Functionality – The computer system – Application of
Unit II : Input Devices
Input Devices: Keyboard – Pointing Devices – webcam – Scanners – Optical character
Recognition – Magnetic Ink Character Recognition – Bar Code Reader. Output devices:
Printers – Plotters – Computer Output Microfilm – Monitors – Voice recognition System –
Unit III : Primary Memory
Primary Memory: Memory Representation – Memory Hierarchy – Random Access Memory
– Read only Memory – Types of ROM.
Secondary Storage: Classification of secondary storage devices – Storage organization of
Magnetic Disk – Storage organization of optical Disk – Magneto Optical Disk – Universal
Serial Bus.
Unit IV : Database Fundamental
Database Fundamental: Data, Information and knowledge – Database – Logical Data
Concepts – Physical Data Concepts – Database Management System – Need, Benefits of
DBMS, Components of DBMS, Database Administrator – DBMS Architecture – Database
Unit V : Internet Basics
Internet Basics: Basic Internet Terms – Internet Addressing – Internet Applications – e-mail,
WWW, File Transfer Protocol, Telnet, Internet Relay Chat, Gopher, Chatting, Commerce
through Internet , Groups, News, Social Networking, Blog, Videoconference, Online services
– E-mail address structure – Sending and Receiving E-mail – Search Engines – Internet and
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Introduction to Computers: Introduction – Characteristics of computersEvolution of computers – Generation of computers – Based on purpose, Based
on type of data handling techniques, and according to Functionality – The
computer system – Application of computers.
1.1 Introduction
We are living in the computer age. Computers can no longer be termed as
mere invention, it is a revolution. Computer revolution has found its way into,
almost every aspect of human life and living. In India, computers are now
being increasingly used and their impact on social, economical, educational and
scientific systems is being greatly felt and recognized.
Literally computer is a calculating machine. We know that a computer is
a fast calculator, but in reality it is much more than that. A computer is an
electronic data processing machine, which receives information, performs basic
operation on that information and produces the output or result according to our
pre-determined conditions specified in the program.
1.1.1 Computerization and Information Technology (IT)
Like the industrial revolution which changed human society, computer
revolution is bringing dramatic shifts in the way we live, perhaps even in the
way we think. The computerization has a great impact on the society, people
and the organizations. Gaining computer literacy has become top priority of
students. Organizations are putting the computers to works, though the
geographical world is large, the information technology world has shrunken
Computerization is essential to survive in the fast world. It is more
necessary to introduce automation especially in industries and big offices due to
advancement in rapid industrialization and the need of faster communication in
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the business dealings. Computerization is changing people‘s life in areas as
diverse as medicine, education, publishing, business, home and transportation.
Computers have completely altered the structure of the business. Large
volumes of accounting, and record keeping, data can be manipulated, organized,
stored, retrieved and used for specific purposes. Financial projections are made
with greater ease.
Word processing saves time for people at all levels of the organization
and helps ensure accurate letters, reports and memos. Automated filing uses far
less storage space than endless stacks of paper and enables workers to retrieve
documents rapidly when they are needed.
Computerizing all phases of activities in transportation, industries and
other services should be accelerated to increase productivity, availability to
focus on economy, cost effectiveness, security and safety. In short,
computerization simply means that the manual work replacement of computer
by using its special features. But this alone is not enough to survive in the fast
developing and competitive world. To catch up the rest of the world by utilizing
the features of computers, the name information technology came into the
ground. The achievement of Information Technology (IT) includes.
-Internet (World Wide computer network)
-Intranet (country wide/Zone wide computer network)
-e-mail (sending/receiving messages using internet)
-e-commerce (financial/ bank dealing using internet)
-e-business (business using internet) etc,.
The effects of IT are
- Possible to handle various types of data such as text, audio and video.
- Functions of various means of transmitting data such as telephone,
telex, television and computers are integrated.
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1.1.2 Computer Related Terminologies
Program: A set of instructions that a computer executes to perform a
series of actions or a particular type of work.
Algorithm: A finite sequence of steps for solving a problem or performing
a task.
Flowchart: A graphical representation of the path of control of the
operations in a program.
Symbols such as squares, diamonds and ovals
represent various operations. These symbols are connected by lines and arrows
to indicate the flow of data or control from one point to another. Flowchart is an
aid to show the way a proposed program will work and as a means of
understanding the operation of a program.
Machine level language: Program written in terms of only 0 and 1.
Machine language is directly executable by a computer. But it is machine
dependent that is different computer need different program.
Assembly level Language: Program written in terms of short codes
namely mnemonics. To execute this program a translator called assembler is
needed to covert from assembly language to machine language. This type of
language is also machine dependent. The machine and assembly language are
called low level languages.
High level language – Program written in languages such as C, C++, java.
To execute this program a translator called compiler or interpreter is needed to
covert from high level language to machine language.
Source code: Human readable program statements written by a
programmer or developer in a high-level or assembly language that are not
directly readable by a computer. Source code need to be compiled into object
code before it can be executed by a computer.
Debugging: To detect, locate and correct logical or syntactical errors in a
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Programmer: An individual who writes and debugs computer programs.
End user: The ultimate user of a computer or computer application in its
finished form.
1.2 Characteristics of Computer
The following are the characteristics of the computer
Storage capacity
The speed of a computer is closely related to the amount of data it must
process. To classify the speed of different computer systems, the industry has
developed the criteria of Million Instructions Per Second (MIPS).
Even the operations of personal computers are measured in thousands of
a second or millisecond (10-3), operations for larger processors are measured in
microseconds (10-6), nanoseconds (10-9) and picoseconds (10-12) etc.
Accuracy refers to the degree of correctness and exactness of operations
performed by a computer. The computer can process data accurately and
quickly. Accuracy is a prime consideration in inventing computers. Computers
never make errors. The errors attributed to computers are really human errors.
The errors may be due to wrongly coded program (code - instructions to
computers) or due to mistakes in input data entry.
Storage capacity
Computer systems have total and instant recall of data and almost
unlimited capacity to store these data. We can store billions of instructions and
perhaps more than thousands of graphic images which are available for instant
recall. When properly used, a computer can improve the efficiency of an
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Computer systems are non-respondent to human factors like fatigue,
tiredness or boredom. Computers can work without getting tired for many
hours. Even though it has no intelligence, it executes the fed instructions
correctly and with accuracy.
The set of instructions are fed into the computer system along with
necessary data. Based on these, the computers automatically perform the
instructions continuously without manual intervention, or supervision.
It is more essential to introduce automation especially in industries and
big offices due to advancement in rapid industrialization and need for quick
interactions in business operations. Computers can do all sorts of automation, if
they are programmed suitably and correctly.
The capability of adopting all kinds of tasks is termed as consistency. It
can perform variety of jobs, ranging from simple arithmetic calculations to
complex graphics modeling, animation, depending on the application packages
loaded into it. Hence, computer can act exactly like an obedient assistant which
can perform tasks repeatedly at high speed with accuracy.
The computer can outperform human beings in speed, memory and
accuracy but still the computer has limitations. They are
Lack of commonsense - The computer is only a tool. It cannot think. It
does not have commonsense and intelligence as we all have. For example,
suppose we give the respective ages of two girls as -12 and 10 and ask a boy to
find out who is younger? The boy will immediately ask how age can be
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But if we give the same data -12 and 10 to a computer it will compare the
two numbers and give the answer ―The younger girl's age is -12." Why?
Because the computer does not have the commonsense to understand that, the
age cannot be less than 0.
Inability to correct - When we give instructions to a computer we must
give the correct instructions. A computer cannot correct wrong instructions.
This follows from the fact that, we cannot replace the human brain by using
Dependency on human instructions - A computer cannot generate any
information on its own. It can only do what it is told to do.
Even though the above mentioned limitations are there, research is going
on in the field of soft computing, to impart knowledge so that it can think and
act independently.
1.3 Evolution of Computer
The computer was born not for entertainment or email but for some
computational purpose. Today, we carry more computing power on our smart
phones than was available in the early models. The following brief history of
computing is a timeline of how computers evolved from their humble
beginnings to the machines of today that surf the Internet, play games and
stream multimedia in addition to crunching numbers.
Abacus – Ancient counting machine. It is a frame with vertical rods, a
horizontal crossbar and beads. It is based on the decimal system: the first
vertical bar is for units, the second for tens and so on. The device was first used
in china around the year 1300.
1614 – Napier Rods – yet another milestone in the quest for manipulating
numbers. John Napier invented a system of movable rods, referred to as
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Napier rods, which allowed for multiplication, division and square, cube
root calculation.
1625 – Slide Rule – can to do many different calculations.
1786 – J.H.Muller, an army officer regards the idea of the Difference Engine.
A difference engine is a special purpose mechanical digital calculator
designed to tabulate polynomial functions, logarithmic and trigonometric
1822 – Charles Babbage designed his first mechanical computer, a prototype for
his difference engine. Babbage invented two machines the Analytical
engine and the Difference engine. Both were too complex to actually be
built. The analytical engine, which Babbage outlined in 1833, used
punched cards for input.
1842-43 – Ada Lovelace wrote to Babbage about a plan for how the difference
engine might calculate Bernoulli numbers. This plan now regarded as the
first computer program.
1848 – British mathematician George Boole devised binary algebra, soon called
Boolean algebra. This was essential for a binary computer to be
1896- Herman Hollerith founded the tabulating machine company, which went
on in 1924, to merge with another company and became International
Business Machine (IBM). IBM is one of the most dominant corporations
of the computer age and secured his place in history as the father of
information processing.
1906- Lee de Forest, invented three-element vacuum tube.
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1937 – Alan Turing invented Turing Machine, a theoretical simplified
1941- Atanasoff and Berry completed a special purpose calculator for solving
simultaneous linear equations; this was later called ABC. Dr. Zuse‘s Z3
computer was designed and was the first automatic, Program-controlled,
fully-functional, general purpose digital computer.
1946 – ENIAC (Electronic Numerical Integrator And Computer) was one of the
first totally electronic, valve-driven and digital computers, designed by
Prosper Eckert and John Mauchly.
1947 – Invention of transistor.
1948 – SSEM (small Scale Experimental Machine) was built based on idea
from John Von Neumann, about stored program computers. This was the
first computer ever to store both programs and data in memory.
Von Neumann is known for the computer architecture which bears his
name – a control unit, an arithmetic and logical unit, memory and
input/output. The Von Neumann architecture is at the heart of the design
of all modern day computers from handhelds to super computer. An
alternative architecture known as the Harvard architecture where the
instructions and data are separately stored is used in some components
like digital signal processors used in audio or video signal processing.
1948 – Claude Shannon identified the bit as the fundamental unit of data. He
also identified it as the basic unit of computation.
1949 – EDVAC (Electronic Discrete Variable Computer) was the first to use
magnetic tape for storage.
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1951 – The UNIVAC I (UNIVersal Automatic Computer), the first commercial
multipurpose computer was delivered.
1953 – A small computer was built using transistors, the first time vacuum
tubes were not used in a computer.
1954 – The NORC (Naval Ordnance Research Calculator) was delivered to the
US Navy. It was the first computer to have been called a super computer.
Magnetic disk storage, high level language FORTRAN and COBOL was
1960-69 – The decade of networking. Time sharing concept, packet switching
comes in. Object oriented programming, the first modem are notable
development in this period.
1970-79 – The innovations, inventions and developments continued in both
hardware and software. The hardware side saw the birth of the
microprocessor, a variety of personal computers, commercial super
computers, the hard disk and more. Computers got smaller. The software
side saw developments in programming languages – C, SQL and many
others. This decade also saw the first generation video game console.
1980-89 – This decade dawn many things that directly constitute the computing
experience of today, such as GUI (Graphical User Interface), the PC,
the Mac system.
1990-99 – Mostly the Internet – The World Wide Web, Linux operating
system, plug and play, Pentium processor, Yahoo directory, Java,
DirectX, Dialup, hotmail, Google etc .
2000 – Till – The new millennium – We are enjoying innovation in dotcom
bubble, variety of operating system, handheld devices, web browsers,
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social media, computing techniques3 etc. Figure 1.1 shows the
developments in computing environment.
Napier Rods
Slide Rule
Analytical Engine
Difference Engine
Turing Machine
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ABC Computer
Z3 Computer
Figure 1.1 Developments in computing environment
1.4 Generations of Computer
Computers are classified into five generations based on the size, memory
capacity, speed, accuracy, electronic technology used in constructing the
computer, the associated system software and applications.
First generation computer
-The period of first generation: 1946-1959
- Built with valves i.e vacuum tubes which were used in old radios and
Limitations of first generation are: Unreliable, Supported machine
only (program written in terms of 0‘s & 1‘s), Very costly, Generated lot of heat,
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Slow input and output devices, Huge size, Need of A.C., Non-portable,
Consumed lot of electricity
Example: ENIAC, EDVAC, UNIVAC, IBM-701, IBM-650
Second generation computer
- The period of second generation: 1959-1965
- Built with solid state transistors and diodes.
Features of second generation are:
compare to first generation
computers, these are reliable, smaller in size, generated less heat, consumed less
electricity, improved speed but costly and need of AC.
Supported machine and assembly (program written in terms of short
codes namely mnemonics) languages.
Example: IBM 1400 series and IBM 7000 series, CDC 3600.
Third generation computer
- The period of third generation: 1965-1971
- Used integrated circuits (IC's) in place of transistors. A single IC has
many transistors, resistors and capacitors along with the associated circuitry.
This development made computers smaller in size, reliable and efficient.
- Compare to previous two generations these are more reliable, smaller in
size, generated less heat, faster, required lesser maintenance
- Supported high-level languages like FORTRAN-II TO IV, COBOL,
- In this generation remote processing, time-sharing, multi-programming
operating system were used.
Example IBM 360, Honey well 200, PDP (Personal Data Processor)
Fourth generation computer
- The period of fourth generation: 1971-1980.
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- Used Very Large Scale Integrated (VLSI) circuits. VLSI circuits having
about 5000 transistors and other circuit elements and their associated circuits on
a single chip made it possible to have microcomputers of fourth generation.
- More powerful, compact, reliable, and affordable. As a result, it gave
rise to personal computer (PC) revolution.
- Concept of internet was introduced; Great developments in the fields of
networks, Computers became easily available
- In this generation time sharing, real time, networks, distributed
operating system were used.
- All the high-level languages like C, C++, DBASE etc., were used.
-Example IBM 370, Honey well 6000 series, PDP 11, CRAY-1(Super
Computer), CRAY-X-MP (Super Computer)
Fifth generation computers
- The period of fifth generation: 1980-till date.
-In the fifth generation, the VLSI technology became ULSI (Ultra Large
Scale Integration) technology, resulting in the production of microprocessor
chips having ten million electronic components.
This generation is based on parallel processing hardware and AI
(Artificial Intelligence) software. All the high-level languages like C and C++,
Java, .Net etc., belongs to this generation.
Main features are: More user friendly interfaces with multimedia,
Availability of very powerful and compact computers at cheaper rates
- Some computer types of this generation are: Desktop, Laptop,
Notebook, Ultra Book and Chrome Book. Figure 1.2 shows the components
used in five generations.
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Vacuum Tubes
LSI circuits
Integrated circuits
VLSI circuits
Figure 1.2 Components used in five generations of computers
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1.5 Classification of Computers
1.5.1 Based on Purpose
According to the field of application the digital computers can be divided
into two categories namely, Special purpose computers and General purpose
A special purpose computer is designed to perform one specific task.
Example: Missile guidance computer.
A general purpose computer is one that has the ability to perform various
operations. Generally, these are capable of carrying out some general data
processing under program control.
1.5.2 Based on type of data handling techniques
Analog Computer
Analog computers work on continuous physical magnitude like length,
pressure, temperature, voltage, current, height, mass, radius etc., which are
analogous to the numbers under consideration.
There are two categories of analog computers: Direct (Special purpose)
and Indirect (General purpose) computers. Direct analog computers are also
known as analog devices. A number of instruments are available that work on
the principles of an analog direct computer.
For example, the Thermometer, though it is not doing any calculation, it
is in a position to precisely measure the temperature of the body by comparing
the relative expansion of mercury.
The Speedometer is in a position to tell
the speed at which the vehicle is running, by comparing the rotational motion of
the shaft of the vehicle. Analog indirect computer operate on analog data by
performing physical processes on these data.
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Digital Computer
A digital computer operates by counting numbers. Digital computers
produce precise results with more accuracy. It can accurately represent data
using as many positions and numbers as necessary.
Adding machines and pocket calculators are common examples of
devices constructed on the principles of the digital computer.
Hybrid computer
Hybrid computers combine the best features of analog and digital
computers. It is a combination of high speed of electronic analog computers and
the accurate-modest size scientific digital computer, linked together by a
communication interface system.
They are usually used for special problems in which input data derived
from measurements, is converted into digits and processed by computer. For
example a hybrid computer controls national defense, fire control system and
passenger flight radar.
The differences between the analog computers and the digital computers
are summarized in the Table 1.1.
Table 1.1 Analog Versus Digital
Analog system
Digital system
Set up analogy of problem
Breaks down problem into arith metic
as Represents numbers as discrete coded
continuous measurement of analogous pattern. Eg. Any digital data
quantity Eg. Presence of pulses,
position, voltage, rotation.
Operations performed by few single Operations performed by relatively
devices.(integrators, many
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multipliers, adders)
devices (registers, accumulators)
Relatively few devices needed.
Many devices needed.
Low cost and ease of programming.
High cost and critical programming.
Distinct elements used for operation. Identical
(Parallel channels).
sequence.(Primary series operation).
Limited accuracy
Unlimited accuracy.
Data storage distributed in various Data storage
non-interchangeable devices.
concentrated in space,
Analog computer serves as model and Digital
mirror relations of actual
system. arithmetic data unrelated to system it
Operations usually carried out in actual represents. Time of
time of physical system.
usually does not correspond to real
Represents physical or mathematical Represents numbers as well
as letters
and other symbols.
1.5.3 According to Functionality
Processing capacity of a computer refers to the volume of data that a
computer system can process. Formerly a computer‘s size was a sign of its
capacity. With the current state of smallness, dimension of capacity is based on
throughput of the computer. Throughput is the quantity of processing that can
be performed in a given amount of time. Based on throughput, computer
systems can be divided into the following categories:
Micro computers (Personal Computers)
The brain of a microcomputer is the microprocessor; it is a silicon chip
containing essential circuits to execute logic or arithmetic operations and to
manage the input/output operations. A microprocessor is an integrated circuit
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which usually contains millions of transistors squeezed onto a small silicon
When the microcomputers were invented it had very limited processing
power and limited choice of input/output devices. Now, they have wider
processing capabilities and maintain a wide range of input/output devices.
The older PC had 8 bit processor with speed of 3.7MB and current PC
has 64 bit processor with speed in terms of GB. Examples: - IBM PCs, Apple
Microcomputers are generally known as personal computers. Desktop
computers are the most common type of PC. Notebook (laptop) computers are
used by people who need the power of a desktop system, but with portability.
Handheld PCs such as PDA, lack the power of a desktop or notebook PC, but
offer features for users who need limited functions and small size. The
difference between desktops and portables
is, portables can be used while
travelling whereas desktops computers cannot be carried around.
The different portable computers are Laptop, Notebooks, Palmtop (hand
held), Mobile slate and Wearable computers
Laptop - This computer is similar to a desktop computers but the size is
smaller. They are expensive than desktop. The weight of laptop is around
3 to 5 kg.
Notebook - These computers are as powerful as desktop but size of these
computers are comparatively smaller than laptop and desktop. They weigh 2 to
3 kg. They are more costly than laptop.
Palmtop (Hand held) - They are also called as PDA. These computers
are small in size. They can be held in hands. It is capable of doing word
processing, spreadsheets and hand writing recognition, game playing, faxing
and paging. These computers are not as powerful as desktop computers.
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Mobile slate – A portable device that is in between laptop and PDA is
mobile slate or PC slate. This is exactly a slate-shaped PC. It weighs around a
kg and is about the size of an A4 sheet.
The PC slate comes with a stylus and a touch enabled screen. The
information written on the slate is converted as text. A stylus is used to touch
the letters, we need to input on a software keyboard.
Wearable Computers – Wearable PCs are like walkman style. In
wearable hands-free PC, voice control acts as an input, miniature display and
head mounted display acts as an output. In this model, applications are
integrated into watches and even clothing. (Figure 1.3)
This is the most appropriate instrument for workers and technicians
working in difficult situations, whose hands must be free for other work. For
example airline technicians and mechanics crawling inside the airline body
attending to repairs, physicians who examine patients etc.
Figure 1.3 Wearable Computers
Workstation or Network Computer
Even though microcomputers are widely used, they have some limitations
in terms of their available memory, disk space and graphics facilities. Further,
their processing speed is also limited.
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PCs are made more powerful with improved performance and are called
as work stations which are generally used by a single user. They symbolize the
bridge between the microcomputers and minicomputers. It is a microcomputer
with many of the facilities and abilities. At first it was designed for use by
designers and engineers who were in need of extremely powerful processing
and output capabilities. Based on their capability, it can be used as a server/
A computer network is a collection of computers connected together.
Servers are not designed to be used directly. They make programs and data
available for users having access to a computer network.
To use servers, users run desktop programs called clients, which contacts
the server and retrieve information from the server. Use of desktop clients and
centralized servers is called client/server computing.
Although terminals look like the personal computers, they have some
limitations when compared with PCs. Terminals have only a screen and a
keyboard and the electronics that allow them to communicate with the computer
to which they are connected. Because they lack the ability to process data on
their own, they are called dumb terminals.
Mini computers
A minicomputer is a medium-sized computer. That is more powerful
than a microcomputer. These computers are usually designed to serve multiple
users simultaneously (Parallel Processing). They are more expensive than
Unlike workstations these computers can be used by several users in a
time-shared mode. These can also be used as a web server to process the
requests and send the requested document through internet.
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Main frame computers
Main frame computers offer extensive benefits over mini and
microcomputers. Some of these have greater storage facility and processing
speed, a larger assortment of input/output devices with multiprogramming and
timesharing capability.
The largest mainframes can handle thousands of dumb and intelligent
terminals and use more than terabytes of secondary storage. An intelligent
terminal has its own processor and do not usually provide any storage.
Mainframes are used in large organizations where many users need access to
shared data and programs. For example these are used to access the bank
account from an automated teller machine. The bank‘s mainframe handles all
the transactions. Complex scientific and engineering problems can also be
processed using mainframes.
Super computers
These are sophisticated, expensive and powerful computers to execute
complex calculations at the maximum speed. Although some supercomputers
are single computer systems, most are comprised of multiple high performance
computers working in parallel as a single system. Supercomputers attain their
high speed by using special techniques like pipelining and parallel processing.
In pipelining, a primary task is subdivided into smaller subtasks. Each
subtask is carried out by the ALU enabling high speed of processing.
Another method to increase the speed of computing is by having multiple
processing units. Part of any calculation can be divided up and done in parallel.
This method is called parallel processing.
Supercomputers are extensively being put to real-time processing
environment. Some areas of applications are military applications, aircraft
control, modeling complex & dynamic system such as world‘s weather, U.S
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economy, motions of galaxies, spiral arms, map the human genome, DNA
structure etc.
The best known supercomputers are built by Cray supercomputers.
CRAY XMP-14 is the first Indian supercomputer. Figure 1.4 shows mainframe
and super computer models.
Figure 1.4 Mainframe and Super computer models
1.6 The Computer System
A computer consists basically of three major units namely input unit, central
processing unit and output unit. (Figure 1.5)
Input unit
The function of the input unit is to read the information contained in the
program and transmit to the central processing unit. The media used for feeding
any information may be of different forms, depending on the facilities available
and the requirement of the situations.
Example of Input devices include Keyboard, Mouse, Magnetic Ink
Character Reader (MICR), Punched card reader, Paper tape reader, Magnetic
tape reader, Tele typewriter, Light pen, etc.,
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Figure 1.5 Block diagram of a computer
Central Processing Unit (CPU)
CPU is the heart of the computer system since the actual computation
work is carried out in this. It links the input and output units together. Internally
it consists of a Memory unit, an Arithmetic Logic Unit (ALU) and Control unit.
Memory is the section where the instructions and data can be stored. All the
intermediate and final results are also stored in the memory.
Arithmetic and Logic Unit
The arithmetic operations such as +, - ,*, / etc as well as logical
comparison are carried out by the ALU and the results obtained are transferred
back to the memory unit for future retrieval.
Control unit
Control unit is playing the overall co-coordinating role in the entire
system. It has direct control over the input and output units. As a program is
being fed into the input unit, the information is converted into binary digits and
stored in the memory, after the initiation from control unit. If the processing
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requires any arithmetic calculation or logical operations to be carried out, the
control unit transfer the relevant data to ALU.
Output unit
On completion of storing all the results of the processed data in the
memory, the control unit transfers the relevant results from the memory unit, to
the output unit in the converted form, which human beings can understand
Some common output devices are printer, plotter and speaker.
1.7 Application of Computers
Computers are used in all walks of our life. They have become so deeply
embedded in information processing and communication systems.
They are used for management applications in factories and companies,
in schools to teach students, in banks to maintain client‘s account, in
engineering offices for the design of buildings or machine components, in
airport for reservation etc. and this list is endless.
Generally computers are used extensively in
Scientific and engineering applications
Satellites and space flight control, military weapons systems, earthquake
calculations, architectural design and drafting.
Business, administrative applications
Payroll, financial accounting, sales analysis and forecasting, Bank
accounting, handling cheques and credit systems.
Humanities applications (Entertainment)
Computer games, house applications, music analysis and composition,
computer art, computer aided instruction and linguistic.
Further more, the applications can be classified into the following six
types of activities:
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Data acquisition (relevant collection)
Data management
1.7.1 Computers in Business
The new trends in IT integrated into business are
Transaction processing – Most business activities involve transactions
with suppliers, employees or customers. Computers make these transactions
easy to use.
Home-based or Mobile Workers – It is easy to connect a computer at
home, to the computer at an office thereby enabling to work at home. These
telecommuters (working at home) enable working at any time, without the
traditional commute. Faster communication makes the home-based business
easier to start and operate.
Desktop Publishing – Producing finished business literature is one of the
uses of computers in business. Using desktop publishing programs and well
featured word processing programs, people can create sales letters, brouchers,
pricelists, newsletters and even very large manuals.
Financial Analysis - Financial analysis is performed in the company,
from top management to all levels. Many tools are available to analyze
investments, sales, expenses, markets and other aspects of business.
1.7.2 Computers in Industry
A computer has a major impact in industries where products are designed
and manufactured. Computer Aided Design (CAD) is used to design products.
Computer Aided Manufacturing (CAM) is used to produce them. The IT
developments in industries are
Product Design – Designing complicated products can require the efforts
of thousands of people work together. This team work is greatly enhanced
through the use of computerized design.
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Automization – Computers are used to run robots to create, finish,
assemble and test products and their components.
Architectural walk-through – To help visualize how a building will really
look like, when it‘s build computerized walk-through are prepared. One
application of this technology on the web is Home building and Home
decoration site. This offers information tips and advice on
- Build offline; plan online and dream a home.
- Estimating material costs and details of materials such as type of
floor, roof etc.
- Tips and information about choosing the right color scheme,
offers a range of shades, estimation of the amount of paint required and the cost
of the paint varieties.
- Find an architect and dealers of the materials needed.
- Designing and decorating the room online.
- Remodeling the home, rearrange the furniture virtually with the
handy room planner.
- Another application offers walk-through an auditorium or
stadium, to select a seat for an event. Before purchase the ticket, we can even sit
in the seat, to see what the angle of view will be like.
In case of business or industry two fundamental computing systems are
- Office Automation
- Management Information Systems
Office automation is defined as using computer and communications
technology to help people for better usage and management of information.
Office automation technology includes all types of computers, telephones,
electronic mail and office machines that use microprocessors or other high
technology components.
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Office automation systems are comprised of many distinct subsystems
like text management systems, business analysis systems, document
management systems and network & communication systems.
Text management systems: These are used for tasks like writing memory
notes, letters and other short documents, printing envelops and labels, preparing
preprinted forms such as invoices, composing complex documents such as
proposals and reports, retrieving and editing documents such as contracts,
creating and display documents like newsletters etc.
Business analysis systems: Managers need solid data from which to
extract the information necessary to make good decisions for the business.
Other software tools for performing analysis that are commonly used in
large companies are decision support system which helps the knowledge worker
to extract information from the various MIS (Management Information System)
data base and reporting systems, analyze it and then formulate a decision or a
strategy for business planning.
An expert system is a computer system that can store and retrieve data
with special problem solving expertise.
An executive support system is an information system that consolidates
and summarizes ongoing transactions within the organization. It provides the
management with all the information it requires at all times from internal as
well as external sources.
Document management systems: Office automation demands that, data be
immediately accessible and instantaneously retrievable. For that reason, we are
slowly moving away from paper and toward document forms that can be stored
on the computer.
Network and communication management system: Today, knowledge
workers have many ways to communicate with one another, primarily by voice,
fax and e-mail. They can communicate in real time, via phone or computer. The
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network and communication management systems include telephone, e-mail,
voice messaging systems, teleconferencing and fax machines.
1.7.3 Computers in Home:
People use home computers generally for the work as they do in their
offices. Word processor, data base programs, personal information management
programs, accounting and income tax calculation programs are useful to do
several activities for home users.
People use home computers for education and information collection.
When the computer is connected to internet, encyclopedias, dictionaries,
telephone directories, medical references, movies and animation are instantly
One can do research work or assignment, join special interest groups,
download files, play games or make airline reservation without leaving home.
Sales catalogs are now being computerized and many catalogs are even
being put on the web, so we can do online shopping. We can buy anything and
pay through Internet banking.
One can read the news paper, magazines, shop advertisement or even
read reviews of the movies in town, through internet.
The multimedia computers provide home entertainment. Most computer
games are simulations, puzzle solving, animations, cartoons with controls; some
other depends on eye-hand coordination.
Computer games can simulate card games, board games, sporting events,
intergalactic battles or something else, real or imaginary. Interesting games can
take people on a tour to solar system, a flight simulator allows both children and
adults to experience being a pilot and learn about the principles of flying.
Computer games are replacing too many real world activities. Instead of
playing music on guitars, one can play music on boom boxes. In general
computer games improve the creativity and concentration.
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1.7.4 Computers in Education
As technology has advanced, educational software has become a major
influence at all levels from elementary schools to universities. Computers have
opened many streams in the field of education. Some of them are
- Carrying out research in the remote fields in the absence of computer is
- Experimenting various exercises pertaining to all subjects
- Using computers as teaching aid in class rooms
- Self learning by students, using various packages to gain knowledge.
The tools such as Computer Aided Instruction (CAI), Computer Based Training
(CBT) are useful for students.
Computers allow students to learn based on the drill-and-practice
principle. The CBT software allow students to learn at their own pace, in small
steps and give feedback about how much they have learned. This method have
the principles namely, individual rate, small steps and positive feedback.
Similar to this, is tutorial software, provides direct instruction in a clearly
specified subject.
Drill-and-practice software and tutorial software are often referred to as
CAI software. One of the major advantages of CAI is individualized learning.
That is, individual students can learn their own pace. Teachers can spend their
time, working with individual students. This is almost impossible in typical
presentation and discussion class rooms.
Education for Kids – Puzzles, crosswords and word games increase
problem solving and comprehensive skills. There are many programs available,
to teach basics such as counting, maths, letters, spelling etc., through interactive
There is no lower limit to use the computer. One can start off even when
the kid is just a year old. The program called ‗lapware‘, gives bright graphics.
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They have to be responsible to any movements on the keyboard and the mouse.
For example, images on the screen changes every time the child touches the
E-learning – It means learning through web, putting up lessons on the
corporate intranet, video broadcasting, CD-ROM based training in conjunction
with real time online personal help, or a combination of these elements. One can
learn almost anything, with e-learning from computer basics to programming,
new technologies and more.
Training programs in business and other organizations are huge and
expensive. To save money and improve performance, companies are using
CBT, to train people on procedures and techniques they need to know in their
jobs. Assume that an organization has several branch offices and the training is
in head office. The advantages of e-learning are many.
- An organization can have employees anywhere in the world, and still
make the same training content available to them.
- Save time on travelling to attend training sessions
- The content can also be made available quickly so that training can
happen in time for the projects to start.
- The employees can access the learning content at anytime of the day or
1.7.5 Computers in Movies
Computers are used in movies to create and enhance the productivity and
performance. Computers are used for, creating special effects in movies, editing
movies, creating full length movies with cartoon characters, multimedia
presentations, composing-editing-recording-reproducing music and sound
Examples of movies which use artificial effects are
Science fiction movies – Starwars, E.T, Matrix
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Special effects in movies – Titanic, Terminator
Cartoon movies – A Bug Life, Toy Story, Antz
Other techniques are, computer controlled lighting, control the images
and sounds using computers, computer animation by projecting series of still
images (frames), etc.
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Input Devices: Keyboard – Pointing Devices – webcam – Scanners – Optical
character Recognition – Magnetic Ink Character Recognition – Bar Code
Reader. Output devices: Printers – Plotters – Computer Output Microfilm –
Monitors – Voice recognition System – Projectors.
2.1 Input Devices -Introduction
Information is entered into a computer through input devices. An input
device converts input information into a suitable binary form acceptable to a
computer. The input units have direct access to the CPU.
The commonly used input devices are keyboard and mouse. Punched card
reader, Paper tape reader, magnetic tape, Magnetic disk are the oldest input
Input devices which do not require typing of input information are
Mouse, joystick, light pen, graphic tablet (graphics input devices), touch screen
and track balls. These allow users to select one of the items or images displayed
on the screen. Therefore, these devices are called pointing devices.
2.2 Keyboard
Keyboard is an input device consisting of a set of typewriter like keys
that enables the user to enter data into a computer. Though it is similar to
typewriter keys, it also contains some additional keys.
Key layouts: The arrangement of keys on the keyboard is termed as the key
layouts. QWERTY and Dvorak-Dealey are the two types of layouts which are
universally used.
The standard layout of letters, numbers and punctuation in QWERTY
keyboard indicates the five keys on the top row of letters QWERTY. Another
keyboard design which has letters positioned for speed typing is the DvorakDealey. This keyboard is developed by August Dvorak and William L.Dealey
and hence named after them. The basic goal is to faster the alteration of hands in
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typing. This keyboard arrangement places all vowels in the home row under the
left hand‘s fingertips and the consonants used most often in the right hand‘s
home row.
Keyboard keys:
The original PC keyboard has 84 keys and enhanced keyboards came
with 101 keys and some with 104 keys. Latest keyboard consists of 107 keys,
with additional hot keys (23 hotkeys) for multimedia applications.
The keyboard keys are classified into the following types:
Alphabetic keys
Numeric keys
Cursor-movement keys
Arrow keys
Modifier keys
Function keys
Special keys
Hot keys
Alphabetic keys: A-Z
Alphabetic characters ‗a‘ to ‗z‘ are typed using these keys. Shift plus
characters or ―Caps lock‖ key ON is used to type capital letters.
Numeric keys: 0-9
Numeric keys are located on the keyboard at two places. One set is in the
top row above alphabetic keys and the other set of these keys are on the right
hand side of the keyboard which can be used with ―Num lock‖ key ON.
Cursor-movement keys:
Cursor is an on-screen blinking character that shows where the new
character will appear. Cursor-movement keys are used to move the cursor on
screen. The standard keys of this type are Arrow keys, Home/End, Tab, Page
up/Page down.
Arrow keys
The arrow keys move the cursor in the direction indicated by the
arrow., , , .
Home – to move the cursor to the beginning of a line
End – to move to the end of a line
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Tab – key moves the cursor to predefined tab stops
Page up – to jump to the previous screen
Page down – to jump to the next screen
Modifier keys
Shift – it is used for typing capital letters and special characters. In
combination with both Ctrl and Alt keys, it is sometimes used to execute a
particular command.
Ctrl, Alt – these keys does not have any purpose. However, combined
with different keys, it performs some useful operation. Some examples are
Ctrl + left arrow – moves to the previous word
Ctrl + Shift + Home – selects all the text to the left of the cursor to the
beginning of the document
Special keys
Punctuation keys – consisting of comma, semicolon, colon etc
Arithmetic keys - , +, _, *, /
Backspace – it moves the cursor to go back by one character and delete it
Spacebar – is used to leave space between words
Enter –In text editing, pressing Enter key moves the cursor to a new line.
In programming it is used to execute the external command.
Delete - to erase the wrongly entered character
Insert – this key is used to insert characters
Print screen – to print the current page of the screen
Scroll lock – to prevent the screen from scrolling
Pause – Temporarily suspend the current task. If the output of the
command exceeds more than one screen, we can see screen by screen by
pressing pause.
Break – to escape from the unhandled error or used for abnormal
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SysRq – keyboard interrupt key
Function keys: F1-F15
These keys are used for specific purposes as defined in the program we
are using. The newer keyboard consists of extra functional keys for increased
productivity. Example includes surfing the internet, running a CD audio player
or opening the mail box etc.
Windows 107 keys
A few functions in window 95 don‘t fall readily under the caps of 104keys keyboard. Three additional keys (two windows key and a popup menu
key) are added to better match the operations of windows.
The two window keys, identified by the zooming window logo on their
caps, serve as attention keys to pop into the windows task manager. One is
located on the left of the left Alt key and the other to the right of the right Alt
key. The third key serves to select the item at which the mouse cursor points,
which is located to the right of the right side window key.
In 107-keys keyboard, the three additional buttons are called sleep,
wakeup and power. The sleep button puts the computer in suspend mode. The
wakeup button pulls it out of suspend mode. The power button works like a
toggle switch for suspend and wakeup. While the computer is on suspend mode,
pressing any other key will also bring it out of suspend mode.
Hot keys
Hot keys are specially meant for multimedia applications. They are
normally placed above the function keys. They look like small round/oval
shaped buttons. Some of the hot keys are
Volume control keys – Mute, Volume increase, Volume decrease
CD player keys – Preview, Play, Next, Stop, Eject
Recorder keys – Review/Play, Record/Stop for audio/Video recording
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Edit Keys: Cut, Copy, Paste
Other short cut keys: Rotate Close, My Document, Game, Calculator, Menu,
WWW, accessing E-mail, instant messenger etc. These keys allow the
multimedia user for faster web surfing and greater efficiency when working
with applications.
2.3 Pointing Devices
A pointer represents a small symbol on the screen. It usually appears on
the screen in Graphical User Interface (GUI) environment. A pointing device is
an input device. It is used to control the movement of the pointer or cursor on
the screen. It can also be used for:
Sending command signals to the computer.
Selecting items on the screen.
Selecting commands from commands menu and Drawing.
Mouse is the most commonly used pointing device, originally referred to as
X-Y Position Indicator. It is used to control the cursor or pointer on the screen
and to give commands to the computer. The mouse is attached with the
computer by a cable or wireless connection. .
Types of mouse
It has a rubber or metal ball at the bottom that can roll in all directions.
Mechanical sensors within the mouse detect the direction. The rolling ball
moves the screen pointer according to the movement.
It uses optical sensors to detect the movement of the ball.
It uses a laser to detect the mouse movement. The mouse is moved along
a special mat with a grid so that the optical mechanism has a frame of reference.
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An optical mouse has no mechanical moving parts. They respond more quickly
and precisely than mechanical and optomechanical mouse.
Functions performed by a mouse:
Double clicking
Clicking and Dragging
are the functions performed by the mouse. It has a left button, a right button,
and a scroll wheel.
Pointing: To point at something on screen, move the mouse until the pointer
points on it.
Clicking: To select an object on the windows screen. For left click on screen
item, press and release the left mouse button once. For right click, point with the
mouse and then press and release the right mouse button.
Double clicking: To start an application. The left button of the mouse is pressed
twice in quick succession by keeping the pointer on the desired object.
Moving: To move the pointer on the desired direction. It helps to point the
object on the screen. No button is pressed while moving the mouse.
Clicking and dragging: To move an object from one place to another. The
selected object moves along with the mouse pointer when it is clicked and
dragged. Hold the left button of the mouse down and move the mouse so that
click and drag is performed. Dragging is also used to draw an item on the
Scrolling: Scrolling the page up and down with the help of a scroller. The small
scroller is placed in between the two buttons.
The mouse also lets users zoom in and out quickly.
A trackball is a pointing input device. It performs functions like a mouse but
it is a stationary device. It has moveable ball on its top. The ball is rotated or
rolled with fingers (or palm of the hand) to move the pointer on the screen. Like
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mouse, a trackball also has buttons that is used to send the commands to
The trackball is usually available with laptop computers. It is fixed on its
keyboard. It is also available as separate input device.
Touch Pad
Touch pad is also known as track pad. This is a pressure-sensitive
pointing device. This stationary device has no moving parts. It is a small, flat
surface (or sensitive pad) over which a user slides fingertip to move the pointer
on the screen.
Touch Pad also has one or two buttons. These buttons are located near the
pad. These buttons work like mouse buttons. Touch Pad is normally used with
Pointing Stick
A pointing stick is a pressure-sensitive pointing device. It looks like a pencil
eraser. It exists between keys of keyboard. It is used to control the movement of
a pointer on the screen. The pointer in the screen moves in the direction in
which the pointing stick is pushed. It is normally used with laptop.
Joystick is a pointing device. It consists of a vertical handle or hand-held
stick, which is mounted on a base. This stick is used to control the movement of
pointer on the screen. Joystick also contains one or two buttons. The button of
the joystick is pressed to activate certain event or action. Joystick is basically
used to play video games. It is also used in some computer-aided design (CAD)
Touch Screen
A touch screen is a special video display screen. Input is given to the
computer directly by touching the screen with user fingertip. Most touch screen
computers use sensors in the computer's screen to detect the touch of a finger.
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Usually touch screens used to make selection from a menu of choices displayed
on the screen. Touch screen is commonly used in ATM. They are also used in
restaurants, supermarkets, departmental stores etc.
In some computer systems, pen-based or light pen input devices are used.
The user touches the screen with a pen. However, the term touch screen implies
a system that accepts input data by touching the screen with the user's fingertip.
Light Pen
The light pen is a hand-held pointing input device. It looks like a pen. It is
a light-sensitive input device. It is connected with the computer by a wire. The
tip of pen contains a light-sensitive element. This device also contains a button.
Input is given to the computer directly by touching the screen with pen.
When the pen touches the screen, it detects or senses a position on display
screen. The user points the object to be selected on the display screen and then
presses a button.
Light Pen device is usually used by engineers and graphic designers. This
input device requires special monitor. Light pen is used in PDA and other types
of hand-held computers.
Digitizer or Graphics Tablet
Digitizer is used for drawing new images or tracing old images. Usually,
it is used for engineering drawings. A digitizer is also known as graphics tablet.
It consists of a flat, rectangular board (or pad) and an input device stylus or
puck. Each location on the rectangular board points to corresponding position
on the computer screen. The stylus or puck is connected to the board / pad by a
Stylus looks like a pen. It is used for drawing images on a specially
designed graphics screen or digitizer. Puck looks like a mouse. Puck is also
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called cursor. Usually, it is used for tracing old images. Figure 2.1 shows some
examples of the pointing devices
Light Pen
Figure 2.1 Examples of pointing devices
2.4 Webcam
A webcam is an input device that captures digital images. A webcam –
short for ‗web camera‘ – is a digital camera that‘s connected to a
computer.(Figure 2.2) It can send live pictures from wherever it‘s sited to
another location by means of the internet
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Unlike a digital camera and digital camcorder, a webcam does not have
any built-in storage. Instead, it is always connected to a computer and uses the
computer hard drive as its storage.
Today, most webcams are either embedded into the display
with laptop computers or connected to the USB or FireWire port on the
computer. Some others are wireless (wifi).
Other features might include:
An integral microphone
The ability to pan and tilt
In-built sensors that can detect movement and start recording
A light that, when on, will let us to know that the camera is in use.
There‘s a wide range of things that we can do with a webcam. Webcams are
mostly used in videoconferencing and for security surveillance. Other uses
include video broadcasting, social video recording and computer vision. The
most common is to video chat over the internet using Skype.
Figure 2.2 Web cam
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2.5 Scanning Devices
Much of the data we want to computerize already exists as hardcopy
(paper) documents. Instead of retyping this data, the scanning devices can scan
(read) documents and transfer it, into the computer.
Scanner is one of the input devices which are used to transfer drawings,
graphs, photographs or text, inside the computer in the form of digital images.
The scanner does an optical scanning mechanism over the information to be
stored. Once the digital representation of the picture is obtained various editing
operations can be performed on it.
A scanner works by passing light at the hard copy being scanned and
measuring intensity of light reflected back using an optical sensor. The amount
of light that is reflected back indicates how light or dark the image is, at each
There are various types of scanners. The most common are Drum, flatbed
and hand scanners. Drum scanners use photomultiplier tubes (PMT). Flatbed
scanners use a glass pane and a bright light. Hand scanners are dragged across
the image manually.
Flatbed scanner
The flatbed scanner is also known as a desktop scanner. The most popular
type of desktop scanner is flatbed scanner, so called because of its flat, glass
platen (or bed) which serves as both the scanning area and surface for laying
objects down to be scanned. Most flatbeds are used for scanning reflective art.
A flatbed scanner works in a similar fashion to a photocopier. The image
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to be scanned is placed on a piece of glass. The scanning beam then moves
across the image. It can also be found mounted with printers.
Flatbed scanners are available in various size and capability. Desktop full
color scanners, large floor model scanners are some of them. They vary in
resolution, Platform size, and color depth. The highest the resolution of the
scanner the sharper will be the image reproduced.
Drum Scanners
Drum scanners use Photo Multiplier Tube ( PMT) technology for greater
dynamic range and color accuracy. Drum scanners can produce more scans per
hour than a flatbed scanner. This offer features such as direct conversion to
CMYK, auto sharpening, batch scanning, greater dynamic range, and huge
image scanning areas.
2.6 Optical Character Recognition (OCR)
It is an input device. It is so designed as to read numeric and alphabetic
character from printed documents.(Figure 2.3) However, the recent OCR‘s can
read handwritten characters.
All OCR systems include an optical scanner for reading text, and
sophisticated software for analyzing images. Most OCR systems use a
combination of hardware and software to recognize characters, although some
inexpensive systems do it entirely through software. It is a common method of
digitizing printed texts so that they can be electronically edited, searched, stored
more compactly, displayed on-line, and used in other machine processes.
Early versions needed to be trained with images of each character, and
worked on one font at a time. Advanced systems are capable of producing a
high degree of recognition accuracy for most fonts. Some systems are capable
of reproducing formatted output that closely approximates the original page
including images, columns, and other non-textual components.
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They can be used for:
OCR is being used by libraries to digitize and preserve their holdings.
Data entry for business documents, e.g. passport, invoice, bank statement
and receipt
Automatic number plate recognition
Automatic insurance documents key information extraction
Extracting business card information into a contact list
More quickly make textual versions of printed documents, e.g. book
Make electronic images of printed documents searchable, e.g. Google
Assistive technology for blind and visually impaired users free guide
Billions of magazines and letters are sorted every day by OCR machines,
considerably speeding up mail delivery.
Figure 2.3 OCR Reader
2.7 Optical Mark Recognition (OMR)
OMR (optical mark recognition) is a form of automated data input. Marks
are made on a specially printed paper forms which are then read by an OMR
reader. The data is then sent to a computer for processing. One of the most
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common uses of OMR is the use of "bubble sheets" in multiple choice
examinations. Students mark their answers on specially printed sheets using
either a pencil or a special marker. The sheets are then collected in and the data
read using a sheet feed OMR scanner. (Figure 2.4)
Other uses are
Attendance registers in schools
Survey forms for market research
Time sheets in factories
Lottery Forms
The advantages are this technology is easy to use and requires little training
and this helps us to easily detect mistakes in an answer sheet.
Figure 2.4 OMR Reader
2.8 Magnetic ink character reader (MICR)
Magnetic ink character recognition code (MICR Code) is a characterrecognition technology used mainly by the banking industry to ease the
processing and clearance of cheques and other documents.
The MICR encoding called the MICR line, is at the bottom of cheques
and other vouchers and typically includes the document-type indicator, bank
code, bank account number, cheque number, cheque amount, and a control
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indicator. The technology allows MICR readers to scan and read the
information directly into a data-collection device. (Figure 2.5)
The ink used in the printing is a magnetic ink or toner, usually
containing iron oxide. The MICR text is passed before a MICR reader. The ink
in the plane of the paper is first magnetized. Then the characters are passed over
a MICR read head, a device similar to the playback head of a tape recorder. As
each character passes over the head it produces a unique waveform that can be
easily identified by the system.
The use of MICR allows the characters to be read reliably even if they
have been overprinted or obscured by other marks, such as cancellation stamps
and signature. This provides a high level of security because any attempt to alter
the magnetic ink printout with normal ink by writing over it will be ignored.
Figure 2.5 MICR Reader
2.9 Bar Code Reader
Bar code reader, also called a price scanner or point-of-sale ( POS )
scanner. Bar Code Reader is a device used for reading bar coded data (data in
the form of light and dark lines). Bar coded data is generally used in labeling
goods, numbering the books etc. It scans a bar coded data, converts it into an
alphanumeric value which is then fed to the computer to which bar code reader
is connected. (Figure 2.6)
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There are five basic kinds of barcode readers -- pen wands, slot scanners,
Charge-Couple Device (CCD) scanners, image scanners, and laser scanners.
A pen wand is the simplest barcode reader. It contains no moving parts. A
pen wand scanner has to remain in direct contact with the bar code, must be
held at a certain angle, and has to be moved over the bar code at a certain
A slot scanner remains stationary and the item with the bar code on it is
pulled by hand through the slot. Slot scanners are typically used to scan bar
codes on identification cards.
A CCD scanner has a better read-range than the pen wand and is often used
in retail sales. Typically, a CCD scanner has a "gun" type interface and has
to be held not more than one inch from the bar code. Each time the bar code
is scanned; several readings are taken to reduce the possibility of errors. The
disadvantage of the CCD scanner is that it cannot read a bar code that is
wider than its input face.
An image scanner, also called as camera reader, uses a small video camera
to capture the image of the bar code and then uses sophisticated digital
image processing techniques to decode the bar code. It can read a bar code
from about 3 to 9 inches away and generally costs less than a laser scanner.
A laser scanner does not have to be close to the bar code for scanning. It
uses a system of mirrors and lenses to allow the scanner to read the bar code
regardless of orientation, and can easily read a bar code up to 24 inches
away. To reduce the possibility of errors, laser scanners may perform up to
500 scans per second. Specialized long-range laser scanners are capable of
reading a bar code up to 30 feet away.
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Figure 2.6 Barcode Reader
2.10 Output Devices
The peripheral devices used to present the results computed by the computer in
a human readable form are called output devices. The output devices receive
results and other information from the computer and provide them to users.
The computer sends information to an output device in a binary form. An
output device converts it into a suitable form convenient to users such as printed
form, display on screen, voice output, etc. The commonly used devices are
monitors, printers and plotters. What you see on the monitor will be printed on
the printer. This is known as ―What You See is What You Get‖ (WYSIWYG).
2.10.1 Printers
Printers are more commonly used output device. Printers are used to
produce printouts or hard copies of the output data from the computer. The
various factors to be considered in selecting a printer are printing speed, onpaper quality, color capabilities, print engine, media of handling and the cost.
According to the method of printing, printers can be classified as follows.
Serial printers (character printers)
Line printers
Page printers
The serial printers can print a character at a time and its speed is
determined by characters per second. It is also classified into two categories
according to the technology employed. They are,
Impact printers
Non-impact printers
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An impact printer contacts with the paper, by pressing an inked ribbon
against the paper using a hammer or pins for printing. Example: Dot matrix
printers and Line printers
Non-impact printers do not use a striking device to produce characters on
the paper, but it sprays ink on the paper. The following tree (Figure 2.7)
summarizes the various classifications of printers with example.
Figure 2.7 Classification of printers
Impact Printers
Dot matrix printers
The dot-matrix printer uses print heads containing from 9 to 24 pins.
These pins produce patterns of dots on the paper to form the individual
characters. The 24 pin dot-matrix printer produces more dots that a 9 pin dotmatrix printer, which results in much better quality and clearer characters. The
more pins, the clearer the characters on the paper. The pins strike the ribbon
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individually as the print mechanism moves across the entire print line in both
The user can produce a color output with a dot-matrix printer by changing
the black ribbon with color stripes ribbon. Dot-matrix printers are inexpensive
and typically print at speeds of 100-600 characters per second.
Daisy-wheel printers
It is called daisy-wheel printer because the print mechanism looks like a
daisy; at the end of each ―Petal‖ is a fully formed character which produces
solid-line print. A hammer strikes a ―petal‖ containing a character against the
ribbon, and the character prints on the paper. It prints typically 25-55 characters
per second.
Line printers
Line printers use special mechanism that can print a whole line at a time.
They can typically print in the range of 1,200 to 6,000 lines per minute. Drum,
chain, and band printers are line printers.
Drum printer
A drum printer consists of a solid, cylindrical drum that has raised
characters in bands on its surface. The number of print positions across the
drum equals the number available on the page. This number typically ranges
from 80-132 print positions. The drum rotates at a rapid speed. For each
possible print position there is a print hammer located behind the paper. These
hammers strike the paper, along the ink ribbon, against the proper character on
the drum as it passes. One revolution of the drum is required to print each line.
This means that all characters on the line are not printed at exactly the same
time, but the time required to print the entire line is fast enough to call them as
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line printers. Typical speeds of drum printers are in the range of 300 to 2000
lines per minute.
Chain printers
A chain printer uses a chain of print characters wrapped around two
pulleys. Like the drum printer, there is one hammer for each print position.
Circuitry inside the printer detects the correct character at the desired print
location on the page. The hammer then strikes the page, pressing the paper
against a ribbon on the character located at the desired print position. An
impression of the character is left on the page. The chain keeps rotating until all
the required print positions on the line have filled. Then the page moves up to
print the next line. Speeds of chain printers range from 400 to 2500 characters
per minute.
Band printers
A band printer operates similar to chain printer except that it uses a band
instead of a chain and has fewer hammers. Band printer has a steel band divided
into five sections of 48 characters each. The hammers on a band printer are
mounted on a cartridge that moves across the paper to the appropriate positions.
Characters are rotated into position and struck by the hammers. Font styles can
easily be changed by replacing the band or chain.
Non-impact printers
Ink-jet printers
Ink-jet printers work in the same fashion as dot-matrix printers. The dots
are formed by tiny droplets of ink. Ink-jet printers form characters on paper by
spraying ink from tiny nozzles through an electrical field that arranges the
charged ink particles into characters at the rate of approximately 250 characters
per second. The ink is absorbed into the paper and dries instantly. Various
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colors of ink can also be used. These printers produce less noise and print in
better quality with greater speed.
Thermal printer
Thermal printing (or direct thermal printing) is a digital printing process
which produces a printed image by selectively heating coated thermo chromic
paper, or thermal paper. When the paper passes over the thermal print head, the
coating turns black in the areas where it is heated, to produce an image. Twocolor
additional color (often red) by applying heat at two different temperatures.
Page Printers
Laser printers
A laser printer works like a photocopy machine. It produce images on
paper by directing a laser beam at a mirror which bounces the beam onto a
drum. The drum has a special coating on it to which toner (an ink powder)
sticks. Using patterns of small dots, a laser beam conveys information from the
computer to a positively charged drum to become neutralized. From all those
areas of drum which become neutralized, the toner detaches. As the paper rolls
by the drum, the toner is transferred to the paper printing the letters or other
graphics on the paper. A hot roller bonds the toner to the paper.
Laser printers use buffers that store an entire page at a time. When a
whole page is loaded, it will be printed. The speed of laser printers is high and
quietly without producing much noise.
2.10.2 Plotters
A plotter is a special output device used to produce hardcopies of graphs
and designs on the paper. A plotter is typically used to print large-format graphs
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or maps such as construction maps, engineering drawings and big posters.
Different types of plotters are
Drum plotter
Flatbed plotter
Inkjet Plotter
Cutting Plotter
Drum Plotter
A drum plotter is also known as Roller Plotter. It consists of a drum or
roller on which a paper is placed and the drum rotates back and forth to produce
the graph on the paper. It also consists of mechanical device known as Robotic
Drawing Arm that holds a set of colored ink pens or pencils. The Robotic
Drawing Arm moves side to side as the paper are rolled back and forth through
the roller to create a perfect graph or map. Drum Plotters are used to produce
continuous output, such as plotting earthquake activity.
Flatbed Plotter
A flatbed plotter is also known as Table Plotter. It plots on paper that is
spread and fixed over a rectangular flatbed table. The flatbed plotter uses two
robotic drawing arms, each of which holds a set of colored ink pens or pencils.
The drawing arms move over the fixed paper and draw the graph on it.
Typically, the plot size is equal to the area of the flat bed. It is used in the design
of cars, ships, aircrafts, buildings, highways etc. Flatbed plotter is very slow in
drawing or printing graphs. The large and complicated drawing can take several
hours to print. The main reason of the slow printing is due to the movement of
mechanical devices.
Mechanical plotters have been replaced by thermal, electrostatic and ink
jet plotters. These systems are faster and cheaper. They also produce large size
Inkjet Plotter
The inkjet plotter creates an image by spraying small droplets of ink on to
paper. A popular choice for advertising agencies and graphic designers, inkjet
plotters are used generally for large outputs, such as banners, billboards and
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large sign boards often seen along roadsides. They are available in thermal or
piezoelectric models. Thermal inkjet plotters use heat to apply droplets of ink,
while piezoelectric plotters use charged crystals to apply the ink. Inkjet plotters
typically produce better quality graphics than other types.
Cutting Plotter
The cutting plotter is a large scale cutting device that produces ready-cut
mylar or vinyl lettering and graphics. Automated plotter knives cut the sheet of
the material lying on the plotter's flat surface area, carving out the design stored
in the computer. Used for sign making, billboard advertising and vehicle
stickers graphics. This devices offer far greater speed and precision than,
traditional method of creating sign lettering and logos by hand.
2.10.3 Computer Output Microfilm
Computer output microfilm (COM Computer Output Microfilm is a
system that converts stored data directly to microfilm or microfiche.(Figure 2.8)
COM technology has been used for document and newspaper archival since
the 1920s. And, with the advent of the personal computer, computer-produced
microforms are becoming more popular for non-library use, such as storing
catalogs and patient records.
COM systems are still used today, mostly by organizations who need to
store payroll, accounting, insurance, inventory, or employee data. Yet because
most of these organizations have outputted the Computer Output Microfilm to
microfiche, they have to manually search for a record and use a reader printer to
save out a particular file.
A more feasible option is to convert Computer Output Microfilm to
digital image via microfiche scanning services. Using high quality/high
production microfiche scanners, we convert the COM microfiche to digital. The
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end result of this entire process is a digital image which we could easily search
the file containing records by name, account number, date, and/or social
security number. Obviously this saves time and efficiency.
Figure 2.8 Computer Output Microfilm
2.10.4 Monitors
Display systems are the focal point of any human-machine interface.
Display systems have been used in digital watches, laptops, mobile phones,
digital cameras, PC monitors, TV etc; this allows seeing exactly, what the PC is
doing as it works. The output on the monitor is called softcopy output.
While monitors come in a variety of shapes, designs, and colors, they can
be broadly categorized into three types. They are
CRT (Cathode Ray Tube) monitors
LCD (Liquid Crystal Display) monitors
LED (Light Emitting Diodes) monitors
Can be either be monochrome or color monitor.
A monochrome monitor is a type of CRT computer display which was
very common in the early days of computing. Monochrome monitors actually
display two colors, one for the background and one for the foreground. The
colors can be black and white, green and black, or amber and black.
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Color monitors can display color ranging from 16 to over 1 million
different colors. These are sometimes called RGB monitors since it uses RGB
as base colors (Red, Green, and Blue).
CRT monitors
These monitors employ CRT technology, which was used most
commonly in the manufacturing of television. With these monitors, a stream of
intense high energy electrons is used to form images on a fluorescent screen. A
cathode ray tube is basically a vacuum tube containing an electron gun at one
end and a fluorescent screen at another end.
The features to be considered are
Monitor screen size is measured diagonally across the screen, in inches.
The resolution of the monitor is the maximum number of pixels it can
display horizontally and vertically (such as 800 x 600, or 1024 x 768, or 1600 x
1200). Most monitors can display several resolutions below its maximum
Pixels (picture elements) are the small dots that display the image on the
The spacing of the screen‘s tiny phosphor dots is called the dot pitch (dp),
typically .28 or .26 (measured in millimeters). A screen with a smaller dot pitch
produces sharper images.
LCD monitors
A flat panel display usually uses an LCD screen to display output from
the computer. The LCD consists of several thin layers that polarize the light
passing through them. The polarization of one layer, containing long thin
molecules called liquid crystals, can be controlled electronically at each pixel,
blocking varying amounts of the light to make a pixel lighter or darker.
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Flat panel displays are much lighter and less bulky than CRT monitors,
and they consume much less power. The display size of a flat panel is expressed
in inches. Cold cathode fluorescent (CCFL) back-lighting is used in LCDs.
Organic Light Emitting Diode (OLED) monitors provide higher contrast
and better viewing angles than LCDs but they require more power when
displaying documents with white or bright backgrounds. Types of OLED are
PMOLED and AMOLED Passive and Active Matrix Organic Light Emitting
Diode respectively.
Plasma Display is another type of flat panel display that utilizes small
cells containing electrically charged ionized gas.
LED monitors: These are flat panel, or slightly curved displays which make use
of light-emitting diodes for back-lighting. The advantages of LED monitors are
that they produce images with higher contrast, have less negative environmental
impact when disposed, more durable than CRT or LCD monitors, does not
produce much heat and feature a very thin design.
2.10.5 Voice Recognition System
Speaker is used to produce audio output that can be heard by the listener.
The sound produced by speakers is defined by frequency and amplitude. The
frequency determines how high or low the pitch of the sound is. A speaker
system's ability to accurately reproduce sound frequencies is a good indicator of
how clear the audio will be. Amplitude, or loudness, is determined by the
change in air pressure created by the speakers' sound waves.
Speakers typically come in pairs, which allow them to produce stereo
sound. This means the left and right speakers transmit audio on two completely
separate channels. By using two speakers, music sounds much more natural
since our ears are used to hearing sounds from the left and right at the same
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For portable laptops and mobile devices, the speakers are built into the
device. Some desktop computers have speakers permanently installed to the
Headphone is used to hear sound output from the computer. They are
similar to speakers, except that, only the person who is wearing the headphone
can hear.
2.10.6 Projectors
This device captures the display of a computer screen and project a large
version of it onto a flat surface. Cathode Ray Tube (CRT) projector, Liquid
Crystal Display (LCD) projector and Digital Light Processing (DLP) projector
are the various types of projector.
CRT projector - In the early days of projectors, CRT projectors were
commonly used. It has three tubes, one for each of the primary colors. Due to
their large size, low light output and the frequent need to converge and align the
images projected from each of the three tubes, they are no longer commonly
LCD projector - LCD projectors work by utilizing polarized mirrors that
pass and reflect only certain colors of light. This causes each channel of red,
green and blue to be separated and later re-converged via a prism after passing
through an LCD panel that controls the intensity and saturation of each color.
An LCD projector can achieve greater brightness at lower energy consumption
and are smaller than CRT projectors
DLP projector - DLP projectors can be classified as one-chip or threechip projectors. One-chip DLP projectors can produce more than 16 million
colors while three-chip models can produce more than 35 trillion colors. This
allows DLP projectors to reproduce more natural and lifelike images
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Primary Memory: Memory Representation – Memory Hierarchy – Random
Access Memory – Read only Memory – Types of ROM.
Secondary Storage: Classification of secondary storage devices – Storage
organization of Magnetic Disk – Storage organization of optical Disk –
Magneto Optical Disk – Universal Serial Bus.
3.1 Computer Memory - Introduction
The function of the memory is to store information. It stores program,
data, results or any other kind of information. Various types of memories are
Main memory or primary memory
Secondary memory or Auxiliary memory
Cache memory
3.2 Primary memory
The memory which is built as a part of the CPU is called the primary
memory or main memory. The memory capacity representation is listed in
Table 3.1
The main memory can be classified into two types as magnetic core
memory and semiconductor memory.
Magnetic core memory
A series of electromagnets are used to represent the characters or
Table 3.1 Memory capacity representations
A binary digit 0,1
8 bits or 1 character
1024 Bytes
1024 KB
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Semiconductor memory
These memories are built by using the flip flops as its basic cell. RAM
and ROM are the two types of semiconductor memory. There are several
variations in RAM and ROM as in Figure 3.1.
Figure 3.1 Categories of RAM and ROM
3.3 Memory Hierarchy
The hierarchical arrangement of storage in current computer architectures
is call the memory hierarchy. The layers of memory in memory hierarchy in
most computers are shown in Table 3.2. The important point to know about the
memory hierarchy is the tradeoffs between speed and size -- the faster the
memory the smaller it is.
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CPU Registers
L1 Cache memory
L2 Cache memory
L3 Cache memory
Main memory - RAM
Rotating magnetic
Optical memory
Table 3.2 Layers of memory in memory hierarchy
The memory hierarchy in most computers is as follows.
 Memory locations built directly into the CPU are called registers.
Processor registers are the special memory locations that are used to hold
the data currently being processed. Each register is typically as wide as
the processors data bus. The processor can read and write data values into
these locations much more quickly than other memory.
The size of the
registers is measured in number of bits, sometimes called word size.
 Storing and retrieving data to and from RAM is one of the time
consuming process. To avoid this complexity, a memory namely Cache
memory in the CPU was introduced. Cache memory is similar to RAM,
except that it is extremely fast.
The most important type of cache memory is the CPU cache. A small
form of memory located directly on the chip itself. It is much smaller, but
can be accessed much faster than the main memory.
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A computer can have several different levels of cache memory (L1, L2,
L3). The level numbers refers to distance from CPU where Level 1 is the
closest. All levels of cache memory are faster than RAM. The cache
closest to CPU is always faster but generally costs more and stores less
data than other level of cache.
RAM - All instructions and storage addresses for the processor must come
from RAM. Although RAM is very fast, there is still some significant time
taken for the CPU to access it (this is termed latency). RAM is stored in
separate, dedicated chips attached to the motherboard and it is much larger
than cache memory.
Magnetic and optical disk - Slow but very large storage capacity.
3.4 Random access memory (RAM) or Read/ Write memory
RAM comprises the main memory of the computer system. The RAM
chips are arranged in rows and installed in the mother board of the computer.
There are two types of RAM namely Dynamic RAM and Static RAM.
Types of RAM
Static Random Access Memory (SRAM)
It consists of flip-flops, a bistable circuit composed of four to six
transistors. Once a flip-flop stores a bit, it keeps that value until the opposite
value is stored in it. SRAM gives fast access to data, but it is physically
relatively large. It is used primarily for small amounts of memory called
registers in CPU and for fast ―cache‖ memory.
Dynamic Random Access Memory (DRAM)
DRAM needs only one transistor cell. The data capacity is at least six
times more than with SRAM. The high density feature and the associated costbenefit ratio of DRAM make it suitable to form the core memory of PC‘s.
The two categories in DRAM are SDRAM (Synchronous DRAM) and
RDRAM (Rambus DRAM).
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Double Data Rate RAM
DDR RAM is already in use in video cards, and now used on computer
motherboards as main RAM. DDR RAM will immediately double the memory
bandwidth available to the processor.
By using this type of memory, the user can expect 5 to 7 percent increase
in memory intensive applications such as Photoshop and CAD based
3.5 Read Only Memory (ROM)
The data are stored permanently in the memory. ROM stores the
programs that are used to boot the computer. ROM's are used extensively in
calculators and peripheral devices such as laser printers, whose fonts are often
stored in ROMs.
The difference between the RAM and the ROM is listed in the Table 3.3.
Table 3.3 Differences between RAM and ROM
The information are stored
Constructed by the manufacturer.
and retrieved by programmer‘s Information stored in this memory
be modified by the
programmer (In EPROM and PROM
modifications are possible.)
Volatile memory i.e. information is
lost during power off.
Non-volatile memory.
Used to store intermediate results.
Permanent function like sin(x), cos(x)
etc are stored for further uses.
Complex and expensive memory
Simple and cheap type of memory
Easy to change.
ROM‘s are expensive to change.
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Types of ROM
Programmable Read Only Memory (PROM).
Used for, the small quantity of user defined applications. PROMs are
manufactured as blank chips on which data can be written. The programming
job is carried by the user.
Erasable Programmable Read Only Memory (EPROM)
In Erasable Programmable Read Only Memory, the contents of memory
locations can be erased by passing the Ultra Violet light. This type of memory is
useful for design and development application, where very frequent changes in
memory contents are required.
Electrically Erasable programmable Read only memory (EEPROM)
The memory locations are cleared electrically and other processes are
similar to the EPROM processes.
3.6 Classification of Secondary Storage devices
There are two main technologies used to store data, namely magnetic and
optical storage. Magnetic storage devices include magnetic disk such as floppy
disk, hard disk, removable hard disk and magnetic tape. Optical storage devices
include CD-ROM, DVD, WORM, magneto optical disk.
Magnetic storage devices record data as magnetic fields. Optical storage
techniques make use of the pinpoint precision that is possible only with laser
The secondary storages are also called as external or auxiliary memory or
backing storage. These devices are used to hold mass information which can be
desirably transferred at any time. Two types of secondary memories, which
have larger capacity are, Magnetic bubble memory and Charge coupled
The advantage of magnetic bubble memory is that the large amount of
data can be stored in a less area. They are considerably faster than
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semiconductor memories. Charge coupled devices (CCD) are volatile memory.
In CCD‘s presence or absence of electric charge represents a bit.
There exist different types of secondary storage devices, each of them
suitable for a specific purpose. They mainly differ in the following aspects:
Technology used to store data, Portability of storage device and Access time.
3.7 Storage organization of Magnetic Disk
The most common physical device for storing files is the magnetic disk.
Actually, a disk typically contains several rotating disks, or platters. The
surfaces of the platters are covered in metal oxide, and read/written by
electromagnetic recording heads.
The surface of a platter is organized as a number of concentric tracks.
Each track is divided into sectors. (Figure 3.2) The information held in one
sector, a block, is the unit of transfer between the disk and primary memory.
The time taken to access a particular block consists of:
Time to move the heads to the right track - the seek time.
Time waiting for the sector to come round to the head - the latency.
Time to actually transfer the data - the block transfer time.
In addition, an empty index is also placed on the disk. The data is stored
in sectors and tracks and the PC locates specific data with the help of the index.
The placing of tracks, dividing them into sectors, and placing of an empty index
is called formatting of the disk. Without formatting, the disk will not accept any
The basic unit of data storage in magnetic disk is called cluster. A cluster
includes two or more sectors. The smallest space that a file can occupy is a
cluster. Depending on the size of the file, it can take, track of the clusters, that
hold the contents of each file.
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Figure 3.2 Track, Sector
3.7.1 Floppy Disk
It is a small, random access disk which can be used for both input and
output operations. Floppy disks are often referred to as diskettes.
The disk is made up of flexible plastic and coated with magnetic oxide.
For protection, it is normally contained within a plastic slave. It can be readily
loaded into and unloaded from a drive unit. The heads on a floppy disk unit
make contact with the disk surface when reading or writing.
The standard sizes of floppy disks are, 8 inches and 5.25 inches, and 3.5
inches. The storage capacity of 8 inch floppy disk ranges from 80 KB to 1,212
KB, 5.25 inch floppy disk ranges from 160KB to 1.2 MB, 3.5 inch floppy disk
ranges from 400 KB to 2.88 MB.
Higher storage capacity floppy disk categories are Zip disks
(100/250MB), Superdisk (120/250MB) and (High Capacity Floppy Disk) HIFD
disk (250MB).
3.7.2 Hard disk
Hard disks are designed to store very high volume of data. Hard disks can
store gigabytes to terabyte of data and they form an integral part of the
computer. Most operating systems are stored in hard disks and all contents
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(application software, documents, images, music files etc) in the computer are
also stored in the hard disk.
The data is stored on a metal platter in the form of magnetic spots. The
metal platter is sealed inside a disk drive that protects the platter and as well
enables reading and writing to the disk.
Hard disk may contain several
platters forming hard disk packs that increase the storage capacity. These
provide fast access for both reading and writing.
Four common hard disk storage technologies are:
ATA (Advanced Technology Attachment)
SCSI(Small Computer System Interface)
RAID (Redundant Array of Inexpensive Disks) and Fiber Channel
3.8 Storage organization of Optical Disk
Optical disk, is any media, read using a laser assembly. The most
common types of optical media are Blu-ray, CDs, and DVDs. Computers can
read and write to CDs and DVDs using a CD Writer or DVD Writer drive, and a
Blu-ray is read with a Blu-ray drive.
Optical memory is used for storing large volumes of data like audio, text,
graphics and video. An optical disk is a removable disk that uses laser to read
and write data. A laser in this context means an electromagnetic wave with a
very specific wavelength within or near the visible light spectrum. Different
types of discs require different wavelengths.
An optical drive that can work with multiple types of discs will therefore
contain multiple lasers. The mechanism to read and write data consists of a
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laser, a lens to guide the laser beam, and photodiodes to detect the light
reflection from the disc.
The optical mechanism for reading CDs and DVDs are quite similar, so
the same lens can be used for both types of discs. The mechanism for reading
Blu-ray discs, however, is quite different. An optical drive that works with all
types of discs will therefore have two separate lenses: one for CD/DVD and one
for Blu-ray. (Figure 3.3)
Figure 3.3 An optical disc drive with separate lenses for CD/DVD and for
Blu-ray discs
In addition to the lens, an optical drive has a rotational mechanism to spin
the disc. Optical drives were originally designed to work at a constant linear
velocity (CLV) - this means that the disc spins at varying speeds depending on
where the laser beam is reading,
This constant speed is very important for music CDs and movie discs,
since we want to listen to music or watch a movie at the regular speed. For other
applications, however, such as reading or writing other types of data, working at
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this speed is not needed. Modern optical drives can often spin much faster,
which results in higher transfer speeds.
An optical drive also needs a loading mechanism. Two general types are in use:
1. A tray-loading mechanism, where the disc is placed onto a motorized
tray, which moves in and out of the computer case.
2. A slot-loading mechanism, where the disc is slid into a slot and motorized
rollers are used to move the disc in and out.
Tray-loading mechanisms for optical drives in desktop computers tend to be
rather bulky. (Figure 3.4)
Figure 3.4 Typically tray-loading optical drive for desktop computers
For laptops, the tray-loading mechanism is much smaller. (Figure 3.5)
Figure 3.5 Typical tray-loading optical
drive for laptop computers
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3.8.1 Compact Disk (CD)
Compact Disk is an optical memory device. It is a non-erasable disk
that stores the digitized audio information. The standard system uses 12cm disks
and they can record more than 60 minutes of playing time without any
CD-ROM – CD-ROM is a read only disk. It is used to hold prerecorded
text, graphics and sound. A CD-ROM disk can hold up to 650MB of data.
Mini CD – CD‘s are available in a smaller 8cm diameter that can store
upto 185 MB of data. A regular CD-ROM drive and CD-writers can be used to
read and write on the mini-CD.
CD-R 74 / 80 / 90 / 99 - In CD-Rs it may found that one of the above
numbers after the CD-R acronym. These numbers refer to the length of
uncompressed audio that can be written to the disc in minutes. 74 minutes is the
industry standard which can contain about 630MB of data. 80 minutes CD-R
can hold about 703 MB of data, a 90 minute about 790 MB, and 870 MB for a
99 minute CD-R.
One popular form of recordable CD is PhotoCD, a standard developed
by Kodak for storing digitized photographic images on a CD. Many filmdeveloping stores have PhotoCD drives that can store photos and put them
onto a CD.
CD-RW – Compact Disk - ReWritable also called as erasable optical disk
allow users to record and erase data so that the disk can be used over and over
3.8.2 Digital Versatile Disk (DVD)
DVD – Digital Versatile Disk (or Digital Video Disk) – It is a High
density CD-ROM disks, which are read by laser and which have both writeonce and rewritable capabilities. There are many variations on the DVD theme.
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There are two physical sizes: 12 cm (4.7 inches) and 8 cm (3.1 inches), both of
1.2 mm thick. These are the same form factors as CD. A DVD disc can be
single-sided or double-sided. Each side can have one or two layers of data. This
can be able to store 4.7 – 17 GB.
DVD-R – DVD disks that allow one time recording by the consumer.
Two types of reusable disks are DVD-RW (DVD rewritable) and DVD-RAM
(DVD Random Access Memory), both of which can be recorded and erased
more than once. There are two formats namely –R, +R.
There are small technical differences in that the +R format allows for
features such as a faster disc eject compared to -R or additional menu functions,
but these differences are negligible in the wider scope of things. Both types of
disc offer 4.7GB of storage.
M-Disc DVD+R - The quite unique M-Disc DVD, made out of a rock like
data layer, the disc is designed to last for 1000 years. It has even been military
tested to withstand the very toughest conditions. The M-Disc has been design to
be read in standard DVD drives. An M-Disc cannot be written in a standard
DVD burner, but requires a dedicated writing drive.
The RW stands for Re-Writable, and it works in the same way as a CDRW. The user can store data to the disc one time or over a period of time, and
can delete data and replace it with new content as required. A DVD-RW has a
thicker coating so it can withstand more wear and tear, and is rated for up to
1000 write operations. The RW format has a storage capacity of 4.7GB.
The DL stands for Dual Layer. This type of DVD disc has almost double
the storage capacity of a DVD-5 format, with a total space availability of
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8.5GB. Physically a DVD-9 disc has the same dimensions as a CD or DVD-5,
but will have a thicker protective lacquer coating to protect the data side.
Some other formats are DVD-10 (12cm, DS/SL): 8.75 GB, DVD-18
(12cm, DS/DL): 15.90 GB- SS/DS means single-/double-sided, SL/DL means
single-/dual-layer. Table 3.4 shows the storage capacity of various optical
Table 3.4 Storage capacity of various optical medium.
Read Only
Write once then Read only
Read Only
Write once then Read only
650 - 900 MB
4.7 - 9.4 GB
Re-Writable and Read Only versions available.
Blu-ray (BD) disc
HD DVD (obsolete)
Uses a blue laser, that is able to recognize
smaller pits and lands, which allows for the pits
25 - 128 GB
and lands to be more closely packed, and so
store more data
3.9 Magneto-optical (M-O) Disk
A storage method used in rewritable optical disk drives that combine
magnetic and optical recording techniques. The disk is coated with film that
initially is uniformly magnetized. A laser beam is used to demagnetize a small
spot on the film by heating it above a critical temperature and a local magnetic
field determines the direction in which the spot is magnetized when it cools. To
read the information, the disk is scanned by polarized light from a low-power
laser. The plane of polarization of the light reflected from a magnetized surface
is rotated according to the direction of the magnetic field. This rotation, though
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small, can be detected and the original binary signal can be reproduced. In early
M-O disk drives data had to be erased separately before it could be rewritten,
but direct rewriting is now possible.
The M-O technique achieves recording densities similar to those of other
optical stores and much higher than has been achieved by magnetic recording.
3.10 Universal Serial Bus (USB)
The Universal Serial Bus (USB) is technology that allows a person to
connect an electronic device to a computer. It is a fast serial bus.
It is mostly used on personal computers. USB is also used on other
devices, like the PlayStation 3, PlayStation 4, the Xbox 360, and others. USB
connects different devices using a standard interface. Connecting point is called
port. (Figure 3.6)
Most people use USB for computer
mice, keyboards, scanners, printers, digital cameras, and USB flash drives.
There are over six billion USB devices around the world.
The standard was made to improve plug and play devices. This means
that a device can be plugged into a free socket, and simply work. The computer
will notice the device. The computer sometimes installs special software so that
the device can directly be used. The device can be removed after it stops being
used. This technology is called "hot swapping". "Hot swapping" means it can be
plugged and unplugged while the power is on. The computer does not need to
be turned off for people to change the devices.
Now, USB has replaced several older standards. Those include
the parallel port, serial port and SCSI. Some special purposes still need those
old connection methods.
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Figure 3.6 USB Port
Several USB transfer speeds are available to provide faster data transfer
rates and support more number of peripheral devices. They are USB 1.X, USB
2.0, also known as hi-speed USB, USB 3.0, also known as Super Speed USB.
USB 3.1, also known as Super Speed, USB Type-C.
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Database Fundamental: Data, Information and knowledge – Database –
Logical Data Concepts – Physical Data Concepts – Database Management
System – Need, Benefits of DBMS, Components of DBMS, Database
Administrator – DBMS Architecture – Database Models.
4.1 Database fundamental: Data, Information and Knowledge
Data represents unorganized and unprocessed facts.
Usually data is static in nature.
It can represent a set of discrete facts about events.
Data is a prerequisite to information.
An organization sometimes has to decide on the nature and volume
of data that is required for creating the necessary information.
Information can be considered as an aggregation of data (processed
data) which makes decision making easier.
Information has usually got some meaning and purpose.
By knowledge we mean human understanding of a subject matter
that has been acquired through proper study and experience.
Knowledge is usually based on learning, thinking, and proper
understanding of the problem area.
Knowledge is not information and information is not data.
Knowledge is derived from information in the same way
information is derived from data.
We can view it as an understanding of information based on its
perceived importance or relevance to a problem area.
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It can be considered as the integration of human perceptive
processes that helps them to draw meaningful conclusions.
Figure 4.1 shows the relationship between data, information and knowledge.
Figure 4.1 Data, Information and Knowledge
Data is unprocessed facts and figures without any added interpretation or
analysis. "The price of crude oil is $80 per barrel."
Information is data that has been interpreted so that it has meaning for the
user. "The price of crude oil has risen from $70 to $80 per barrel" gives
meaning to the data and so is said to be information to someone who tracks
oil prices.
Knowledge is a combination of information, experience and insight that may
benefit the individual or the organization. "When crude oil prices go up by
$10 per barrel, it's likely that petrol prices will rise by 2$ per litre" is
4.2 Hierarchy of data organization
In database system concept, the single data or data element is referred to
as a field and information is referred to as a record. Collection of related records
forms a file.
A database is a collection of the occurrences of multiple records,
containing the relationship between records and fields. One more concept is a
databank, which refers to a collection of databases.
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For example, Register number, Mark1, Mark2, Mark3, Total, Grade are
individual fields. A student record is the collection of all the above data fields.
Suppose, if there are 40 students in a class, then the collection of 40 records will
form the file called student-academic-file. Grouping of related file namely,
Student-academic-file and student-personal-file (consists of Father‘s-name,
occupation, address etc.,) , will form a Student database. In a college, one must
maintain the databases of all the department student‘s details, to form a
databank. (Figure 4.2)
Figure 4.2 Hierarchy of data organization
A database is a collection of information that is organized so that it can
easily be accessed, managed, and updated. In one view, databases can be
classified according to types of content: bibliographic, full-text, numeric, and
images. Usually the database is organized in the form of table with rows and
4.3 Data Modeling, Key, Normalization
There are a lot of new terms to learn when we begin to study the
Entity: An entity is a person, place, thing or concept about which, data can be
collected. Examples include Employee, house, Car.
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Attributes: Each entity is made up of a number of 'attributes' which represent
that entity, also known as property of an entity. An attribute describes the facts,
details or characteristics of an entity.
Entity = Customer. Attributes for the entity customer are Customer ID,
First Name, Last Name, Date of Birth, Address, Phone number etc.
Relationship: Link between entities.
Example: Employee and family – One-to-one relationship
Employee and house – One- to-many relationship
Family members and car – Many-to-one relationship
To set up a database, we should work out:
- The entities - The attributes - The entity relationships
This process is called 'data modeling'
Primary Key
A primary key is a main reference key for the table. As its name suggests,
it is the primary key of reference for the table and is used throughout the
database to help establish relationships with other tables. The primary key must
contain unique values, must never be null and uniquely identify each record in
the table.
As an example, a studentid might be a primary key in a student table.
Primary keys are mandatory for every table and each record must have a value
for its primary key. (Figure 4.3)
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Figure 4.3 Primary Key
Foreign Key
A foreign key is generally a primary key from one table that appears as a
field in another where the first table has a relationship to the second. In other
words, if we had a table A with a primary key X that linked to a table B where
X was a field in B, then X would be a foreign key in B.
An example might be a student table that contains the courseid the
student is attending. Another table lists the courses on offer with courseID being
the primary key. The 2 tables are linked through courseID and as such courseID
would be a foreign key in the student table. (Figure 4.4)
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Figure 4.4 Foreign Key
- It is the process of organizing data into related table.
- To normalize database, we divide database into tables and establish
between the tables.
- This is performed by creating relationships among tables through primary and
foreign keys.
- It reduces redundancy. It is done to improve performance of query.
- Steps of normalization:
First Normal form
-Entities of the table must have unique identifier or entity key.
Second Normal Form
- All the attributes of the table must depend on the entity key for
that entity.
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Third Normal Form
-All attributes that are not part of the key must not depend on any
other non-key attributes.
The process of adding redundant data to get rid of complex join, in order
to optimize database performance. This is done to speed up database access by
moving from higher to lower form of normalization.
4.4 Logical Data Concepts
A logical data model describes the data in as much detail as possible,
without regard to how they will be physical implemented in the database.
Features of a logical data model include:
Includes all entities and relationships among them.
All attributes for each entity are specified.
The primary key for each entity is specified.
Foreign keys (keys identifying the relationship between different entities)
are specified.
Normalization occurs at this level.
The steps for designing the logical data model are as follows:
 Specify primary keys for all entities.
 Find the relationships between different entities.
 Find all attributes for each entity.
 Resolve many-to-many relationships.
 Normalization.
The Figure 4.5 is an example of a logical data model.
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Figure 4. 5 Example of Logical Data Model
4.5 Physical Data Concepts
Physical data model represents how the model will be built in the
database. A physical database model shows all table structures, including
column name, column data type, column constraints, primary key, foreign key,
and relationships between tables. Features of a physical data model include:
Specification all tables and columns.
Foreign keys are used to identify relationships between tables.
Denormalization may occur based on user requirements.
Physical considerations may cause the physical data model to be quite
different from the logical data model.
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Physical data model will be different for different RDBMS. For example,
data type for a column may be different between MySQL and SQL
The steps for physical data model design are as follows:
 Convert entities into tables.
 Convert relationships into foreign keys.
 Convert attributes into columns.
 Modify the physical data model based on physical constraints /
The figure 4.6 is an example of a physical data model.
Figure 4.6 Example of Physical Data Model
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Comparing the physical data model shown above with the logical data
model diagram, we see the main differences between the two:
Entity names are now table names.
Attributes are now column names.
Data type for each column is specified. Data types can be different
depending on the actual database being used.
4.6 Data Base Management System (DBMS)
A Database is a collection of related data organized in a way that, data
can be easily accessed, managed and updated. A DBMS is software that allows
creation, definition and manipulation of database. DBMS is actually a tool used
to perform any kind of operation on data in database. DBMS also provides
protection and security to database. It maintains data consistency in case of
multiple users. Some examples of popular DBMS are MySql, Oracle, Sybase,
Microsoft Access and IBM DB2 etc.
4.6.1 Need of DBMS
* A DBMS is important because it manages data efficiently and allows users
to perform multiple tasks with ease.
* It stores, organizes and manages a large amount of information within a
single software application.
* Use of this system increases efficiency of business operations and reduces
overall costs.
* It is important to businesses and organizations because they provide a highly
efficient method for handling multiple types of data.
* Without DBMS, tasks have to be done manually and take more time.
* Data can be categorized and structured to suit the needs of the company or
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* Multiple users can use the system at the same time in different ways. For
example, a company's human resources department uses the database to manage
employee records, distribute legal information to employees and create updated
hiring reports. A manufacturer might use this type of system to keep track of
production, inventory and distribution. In both scenarios, the DBMS operates to
create a smoother and more organized working environment.
4.6.2 Benefits of DBMS
The DBMS has a number of benefits compared to traditional computer file
processing approach. The following are main benefits
Controlling Data Redundancy:
In traditional computer file processing, each application program has its
own data. In this case, the duplicated copies of the same data are created at
many places. In DBMS, all the data of an organization is integrated into a single
database. The data is recorded at only one place in the database and it is not
duplicated. For example, the principal‘s faculty file and the faculty payroll file
contain several items that are identical. When they are converted into database,
the data is integrated into a single database so that multiple copies of the same
data are reduced to-single copy. By controlling the data redundancy, we can
save storage space. Similarly, it is useful for retrieving data from database using
Data Consistency:
If a data item appears only once, any update to its value has to be
performed only once and the updated value (new value of item) is immediately
available to all users.
If the DBMS has reduced redundancy to a minimum level, the database system
enforces consistency. It means that when a data item appears more than once in
the database and is updated, the DBMS automatically updates each occurrence
of a data item in the database.
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Data Sharing:
In DBMS, data can be shared by authorized users of the organization.
Many users can be authorized to access the same set of information
simultaneously. The remote users can also share same data. Similarly, the data
of same database can be shared between different application programs.
Data Integration:
In DBMS, data in database is stored in tables. A single database contains
multiple tables and relationships can be created between tables (or associated
data entities). This makes easy to retrieve and update data.
Integrity Constraints:
Integrity constraints or consistency rules can be applied to database so
that the correct data can be entered into database. The constraints may be
applied to data item within a single record or they may be applied to
relationships between records.
The examples of integrity constraints are:
(i) 'Issue Date' in a library system cannot be later than the corresponding 'Return
Date' of a book.
(ii) Maximum obtained marks in a subject cannot exceed 100.
(iii) Registration number of BCS and MCS students must start with 'BCS' and
'MCS' respectively etc.
There are also some standard constraints that are intrinsic in most of the
DBMSs. These are shown in Table 4.1.
Data Security:
Data security is the protection of the database from unauthorized users.
Only the authorized persons are allowed to access the database. Some of the
users may be allowed to access only a part of database i.e., the data that is
related to them or related to their department. Mostly, the Data Base
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Administrator (DBA) or head of a department can access all the data in the
database. Some users may be permitted only to retrieve data, whereas others are
allowed to retrieve as well as to update data. The database access is controlled
by the DBA. He creates the accounts of users and gives rights to access the
database. Typically, users or group of users are given usernames protected by
Table 4.1 Standard Constraints
Data Atomicity:
A transaction in commercial databases is referred to as atomic unit of
work. For example, when we purchase something from a point of sale (POS)
terminal, a number of tasks are performed such as;
Company stock is updated.
Amount is added in company's account.
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Sales person's commission increases etc.
All these tasks collectively are called an atomic unit of work or transaction.
These tasks must be completed in all; otherwise partially completed tasks are
rolled back. Thus through DBMS, it is ensured that only consistent data exists
within the database.
Database Access Language:
Most of the DBMSs provide SQL as standard database access language.
It is used to access data from multiple tables of a database.
Development of Application:
The cost and time for developing new applications is also reduced. The
DBMS provides tools that can be used to develop application programs. For
example, some wizards are available to generate Forms and Reports. Stored
procedures (stored on server side) also reduce the size of application programs.
Creating Forms:
Form is very important object of DBMS. A Form provides very easy way
(user-friendly interface) to enter data into database, edit data, and display data
from database. The non-technical users can also perform various operations on
databases through Forms without going into the technical details of a database.
The Forms can be created very easily and quickly in DBMS, Once a Form is
created, it can be used many times and it can be modified very easily. The
created Forms are also saved along with database and behave like a software
Report Writers:
Most of the DBMSs provide the report writer tools used to create reports.
The users can create reports very easily and quickly. Once a report is created, it
can be used many times and it can be modified very easily. The created reports
are also saved along with database and behave like a software component.
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Control over Concurrency:
In a computer file-based system, if two users are allowed to access data
simultaneously, it is possible that they will interfere with each other. For
example, if both users attempt to perform update operation on the same record,
then one may overwrite the values recorded by the other. Most DBMSs have
sub-systems to control the concurrency so that transactions are always recorded"
with accuracy.
Backup and Recovery Procedures:
In a computer file-based system, the user creates the backup of data
regularly to protect the valuable data from damaging due to failures to the
computer system or application program. It is a time consuming method, if
volume of data is large. Most of the DBMSs provide the 'backup and recovery'
sub-systems that automatically create the backup of data and restore data if
required. For example, if the computer system fails in the middle (or end) of an
update operation of the program, the recovery sub-system is responsible for
making sure that the database is restored to the state it was in before the
program started executing.
Data Independence:
The separation of data structure of database from the application program
that is used to access data from database is called data independence. In DBMS,
database and application programs are separated from each other. The DBMS
sits in between them. We can easily change the structure of database without
modifying the application program. For example we can modify the size or data
type of a data items (fields of a database table).
On the other hand, in computer file-based system, the structure of data
items is built into the individual application programs. Thus the data is
dependent on the data file and vice versa.
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Advanced Capabilities:
DBMS also provides advance capabilities for online access and reporting
of data through Internet. Today, most of the database systems are online. The
database technology is used in conjunction with Internet technology to access
data on the web servers.
4.7 Components of DBMS
A DBMS consists of several components. Each component plays very
important role in the database management system environment. The major
components of DBMS are (Figure 4.7)
Database Access Language
Figure 4.7 Components of DBMS environment
The main component of a DBMS is the software. It is the set of programs used
to handle the database and to control and manage the overall computerized
DBMS software itself, is the most important software component in the
overall system
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Operating system, network software used to share the data of database
among multiple users.
Application programs developed in programming languages such as C++,
Visual Basic that are used to access database in DBMS. Each program
contains statements that request the DBMS to perform operation on
database. The operations may include retrieving, updating, deleting data
Hardware consists of a set of physical electronic devices such as
computers (together with associated I/O devices like disk drives), storage
devices, I/O channels, electromechanical devices that make interface between
computers and the real world systems etc, and so on. It is impossible to
implement the DBMS without the hardware devices. In a network, a powerful
computer with high data processing speed and a storage device with large
storage capacity is required as database server.
Data is the most important component of the DBMS. The main purpose
of DBMS is to process the data. In DBMS, databases are defined, constructed
and then data is stored, updated and retrieved to and from the databases. The
database contains both the actual (or operational) data and the metadata (data
about data or description about data).
Procedures refer to the instructions and rules that help to design the
database and to use the DBMS. The users that operate and manage the DBMS
require documented procedures on hot use or run the database management
system. These may include.
Procedure to install the new DBMS.
To log on to the DBMS.
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To use the DBMS or application program.
To make backup copies of database.
To change the structure of database.
To generate the reports of data retrieved from database.
Database Access Language
The database access language is used to access the data to and from the
database. The users use the database access language to enter new data, change
the existing data in database and to retrieve required data from databases. The
user writes a set of appropriate commands in a database access language and
submits these to the DBMS. The DBMS translates the user commands and
sends it to a specific part of the DBMS called the Database Jet Engine. The
database engine generates a set of results according to the commands submitted
by user, converts these into a user readable form called an Inquiry Report and
then displays them on the screen. The administrators may also use the database
access language to create and maintain the databases.
The most popular database access language is SQL (Structured Query
The users are the people who manage the databases and perform different
operations on the databases in the database system. There are three kinds of
people who play different roles in database system
Application Programmers
Database Administrators
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Application Programmers
The people who write application programs in programming languages
(such as Visual Basic, Java, or C++) to interact with databases are called
Application Programmer.
Database Administrators
A person who is responsible for managing the overall database
management system is called database administrator or simply DBA.
The end-users are the people who interact with database management
system to perform different operations on database such as retrieving, updating,
inserting, deleting data etc.
4.8 Data Base Administrator (DBA)
A database administrator (DBA) directs or performs all activities related
maintaining all databases required for development, testing, training and
production usage, managing share resources used amongst applications. Some
other responsibilities are
* Administrates all database objects, including tables, views, indexes, stored
procedures, functions, packages etc.
* Enforces and maintains database constraints to ensure integrity of the database
* Installation and configuration of DBMS server software and related products
* Upgrading and patching/hot-fixing of DBMS server software and related
* Assists with impact analysis of any changes made to the database objects
* Migrating database to another server
* Evaluate DBMS features and DBMS related products
* Ensure that the site is running the products that are most appropriate
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* Ensure that any new product usage or release upgrade takes place with minimal
*Establish and maintain sound backup and recovery policies and procedures.
* Take care of the Database design and implementation.
* Implement and maintain database security (create and maintain logins, users
and roles, assign privileges).
* Performance tuning and health monitoring on DBMS, OS and application.
* Setting up Server Level, Database Level and Operating System Alerts
* Implementation of robust maintenance plan
* Setup and maintain documentation and standards.
*Perform reviews on the design and code frequently to ensure the standards are
being adhered to
*Plan growth and changes (capacity planning).
* Do general technical troubleshooting and give consultation to development
* Troubleshooting on DBMS and Operating System performance issue
* Documentation of any implementation and changes (database changes,
reference data changes and application User Interface changes etc)
* Be able to provide a strategic database direction for the organization.
4.9 DBMS Architecture
Database architecture is logically divided into two types.
Logical two-tier Client / Server architecture
Logical three-tier Client / Server architecture
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Two-tier Client / Server architecture
Figure 4.8 Two-tier Client / Server architecture
Two-tier Client / Server architecture is used for User Interface program
and Application Programs that runs on client side (Figure 4.8). An interface
called ODBC (Open Database Connectivity) provides an API (Application
Programming Interface) that allows client side program to call the DBMS. Most
DBMS vendors provide ODBC drivers. A client program may connect to
several DBMS's. In this architecture some variation of client is also possible for
example in some DBMS's more functionality is transferred to the client
including data dictionary, optimization etc. Such clients are called Data server.
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Three-tier Client / Server architecture
Figure 4.9 Three-tier Client / Server architecture
Three-tier Client / Server database architecture is commonly used
architecture for web applications. Intermediate layer called Application
server or Web Server stores the web connectivity software and the business
logic (constraints) part of application used to access the right amount of data
from the database server (Figure 4.9). This layer acts like medium for sending
partially processed data between the database server and the client.
4.10 Data Base Models
A database model is a logical structure of a database and fundamentally
determines the manner in which the data can be stored, organized, and
manipulated. Common logical data models for databases include:
 Flat model
 Hierarchical model
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 Network model
 Relational model
 Object model
 Entity–relationship model
Flat model
The flat model is the earliest, simplest data model. It simply lists all the
data in a single table, consisting of columns and rows. In order to access or
manipulate the data, the computer has to read the entire flat file into memory,
which makes this model inefficient for all but the smallest data sets Figure 4.10.
Figure 4.10 Flat File Model
Hierarchical model
In this model each entity has only one parent but can have several
children. At the top of hierarchy there is only one entity which is called root.
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(Figure 4.11)
Figure 4.11 Hierarchical Model
Network Model
In the network model, entities are organized in a graph, in which some
entities can be accessed through several paths. (Figure 4.12)
Figure 4.12 Network Model
Relational Model
In this model, data is organized in two-dimensional tables
called relations. The tables or relation are related to each other. (Figure 4.13)
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Figure 4.13 Relational Model
Object model
This model defines a database as a collection of objects, or reusable
software elements, with associated features and methods. (Figure 4.14 )There
are several kinds of object-oriented databases:
A multimedia database incorporates media, such as images, that could
not be stored in a relational database.
A hypertext database allows any object to link to any other object. It‘s
useful for organizing lots of disparate data, but it‘s not ideal for numerical
The object-oriented database model is the best known post-relational
database model, since it incorporates tables, but isn‘t limited to tables. Such
models are also known as hybrid database models.
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Figure 4.14 Object model
Entity-relationship model
This model captures the relationships between real-world entities much
like the network model, but it isn‘t as directly tied to the physical structure of
the database. Instead, it‘s often used for designing a database conceptually
(Figure 4.15).
Here, the people, places, and things about which data points are stored are
referred to as entities, each of which has certain attributes that together make up
their domain. The cardinality, or relationships between entities, is mapped as
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Figure 4.15 Entity-relationship model
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Internet Basics: Basic Internet Terms – Internet Addressing – Internet
Applications – e-mail, WWW, File Transfer Protocol, Telnet, Internet Relay
Chat, Gopher, Chatting, Commerce through Internet , Groups, News, Social
Networking, Blog, Videoconference, Online services – E-mail address structure
– Sending and Receiving E-mail – Search Engines – Internet and Viruses.
5.1 Internet Introduction
The Internet is a worldwide, publicly accessible series of interconnected
computer networks that transmit data by packet switching using the standard
Internet Protocol.
The U.S. department of defense established a program called Advanced
Research Projects Agency Network (ARPANET) in 1969, to provide a secure
communications network for defense related research. After undergoing several
transformations, the internet has become what it is today.
Vinton Cerf and Robert Kahn developed the first description of the TCP
protocols in 1973. The term ―Internet‖ was first used in 1974 to describe a single
global TCP/IP network detailed in the first full specification of TCP written by
Cerf and his colleagues. The first TCP/IP-Wide Area Network was created on
January 1, 1983 when all hosts on the ARPANET were switched over from the
older protocols to TCP/IP.
5.2 Basic Internet Terms
Computers are connected together to form a network. The communication
among them is originally attained by the network operating system. As the
number of computers connected to the network increased and the computers
running on the different operating system needed to communicate with each
other, the necessity of standardization in the communication arised.
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Standardization in communication is achieved in the areas of,
Communication protocol, addressing scheme and service providers
Communication protocol
Information is transmitted over the internet in the form of packets. When
a piece of information is sent to another user on the internet, the information is
broken down into packets of fixed size and sent. In the destination machine, the
packets are reassembled as information.
A protocol is simply an agreed set of standards that allows computers to
communicate one another. The name of the protocol may change according to
the internet service. The protocol (rules) used to transfer packets across the
internet is called Internet Protocol (IP) and the protocol that breaks the
information into packets and reassembles it, is Transmission Control Protocol
(TCP). Hence the standard for communication on the internet is called TCP/IP.
TCP/IP transfers information in small units called packets. Each packet
- The identification of the source computer from where the data arises
- The destination computer to which it is addressed
- The data itself
- The error checking mechanism to confirm that the individual packet was
accurately and completely sent and received.
In order to speed up the data transmission, the TCP/IP can break the large
file into multiple packets, each sent over the different paths in the network.
These packets are then reassembled at the other end into one file, and saved in
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the destination computer. The TCP/IP determines addressing mechanisms and
the routing of packets.
Addressing scheme
Some form of identification is needed, to send information between
computers. The web address which provides this identification is called
Uniform Resource Locator (URL). It is composed of a specific string of
characters, consisting of,
- a protocol
- a host name
- a directory
- a file name
- a port
Each page on the web has its own unique URL. Even some elements on a
page have separate URL‘s. For example a graphic in a page have a URL, which
is slightly different from the page URL.
http – specifies the protocol, in this case hyper text transfer protocol ( the
language that www uses to tie the pages together). The protocol is followed by a
colon. – part of the address called a domain name, is
preceded by two slashes. This is the name assigned to a computer, located
somewhere in the world that is permanently connected to the web. Here www
stands for World Wide Web; netscape is the name of the organization hosting
the site; .com is the identification of the type of organization hosting the site
(called top most domain).
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/new/index.html is the path to a file, meaning that the document
index.html is stored in a folder named /new.
#download is called a fragment ID. This is the name of a specific part of
the document.
Internet Service Providers (ISP)
To access the internet one need an ISP. The ISP is connected to the
internet backbone, which is the permanent cabling of the internet. This
backbone may consist of copper wire, fiber optic cable, microwave and even
satellite connections between any two points. The Internet Service Providers
govern the internet. They are the authorized people to provide the internet
In our country BSNL (Bharat Sanchar Nigam Limited) is one of the
service providers. Some private concerns who provide this service are Aircel ,
Reliance Communications, Tata DoCoMo , and Tata Indicom. Private Service
providers have to obtain a national wide ISP license from Department Of
Telecommunication (DOT).
5.3 Internet Addressing
An Internet address uniquely identifies a node on the Internet. Internet
address may also refer to the name or IP of a Web site (URL). The term Internet
address can also represent someone's e-mail address.
5.3.1 IP Address
IP addressing is a hardware-independent convention which in principle
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unique logical address. IP addresses are currently 32-bit binary strings, in dotted
decimal such as
The 32-bit address is broken up into four 8-bit sequences each of which is
converted to decimal. So the above address in binary is:
11011111 00111010 00000001 00001010
IP Address Formats
Internet addresses combine – a routing portion, known as the network
part – a name portion known as the host part „ How to split an Internet address
into the network part and the host part has changed over time. Originally IP
addresses were divided into five classes as shown below. Classes A, B and C
are the most important: the initial bits determine which class an address belongs
to, and the classes differ in how much of the address is taken up with
the network address and how much with the host address.
0 Network
Class A
Addresses to
Class B
10 Network
Addresses to
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Class C
110 Network
Addresses to
Class D
1110 Multicast address
Addresses to
Class E
11110 Reserved for future use
Addresses to
The designers of the Internet Protocol defined an IP address as a 32bit number and this system, known as Internet Protocol Version 4 (IPv4), is still
the Internet and
predicted depletion of available addresses, a new version of IP (IPv6), using 128
bits for the address has been established. The address size was increased from
32 to 128 bits , thus providing up to 2128 (approximately 3.403×1038) addresses.
This is deemed sufficient for the foreseeable future.
The Internet Assigned Numbers Authority (IANA) manages the IP
address space allocations globally and delegates five Regional Internet
Registries (RIRs)
to local
registries (Internet service providers) and other entities.
Currently, classless addressing is in use providing arbitrary host and
network part lengths.
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5.3.2 Domain Name
In general, a domain name represents an Internet Protocol (IP) resource,
such as a personal computer used to access the Internet, a server computer
hosting a web site, or the web site itself or any other service communicated via
the Internet. It is an identification string used in various networking contexts
and application-specific naming and addressing purposes. Domain names are
formed by the rules and procedures of the Domain Name System (DNS).
Domain names are organized in subordinate levels (sub domains) of
the DNS root domain, which is nameless. The first-level set of domain names
the top-level
domains (TLDs),
the generic
domains (gTLDs), such as
com -commercial (business)
edu – education
net – organizations directly involved in internet operations
org – organization
gov – government
mil –military
and the country code top-level domains (ccTLDs) such as
in- India
us – United States
de - Germany
Each TLD has a separate registry managed by a designated organization
under the direction of the Internet Corporation for Assigned Names and
Numbers (ICANN).
Below these top-level domains in the DNS hierarchy are the second-level
and third-level domain names that are typically open for reservation by endusers who wish to connect local area networks to the Internet, create other
publicly accessible Internet resources or run web sites. The registration of these
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domain names is usually administered by domain name registrars who sell their
services to the public.
A fully qualified domain name (FQDN) is a domain name that is
completely specified in the hierarchy of the DNS, having no parts omitted. Most
commonly domain names are written in lowercase in technical contexts.
Domain names are used to establish a unique identity. Organizations can
choose a domain name that corresponds to their name, helping Internet users to
reach them easily.
ICANN identifies the following categories of TLDs:
Country-code top-level domains (ccTLD) -- Each ccTLD identifies a
particular country and is two letter long. The ccTLD for the United States,
is .us
Infrastructure top-level domain -- There is only one TLD in this group,
ARPA (Address and Routing Parameter Area). The Internet Assigned
Numbers Authority (IANA) manages this TLD for the IETF (Internet
Engineering Task Force).
Sponsored top-level domains (sTLD): These are overseen by private
Generic top-level domains (gTLD) -- These are the most common and
familiar TLDs. Examples include "com" for "commercial" and "edu" for
"educational." Most gTLDs are open for registration by anyone, but there is
also a subgroup that is more strictly controlled.
For example, com is the top-level domain
name; techtarget is the second-level domain name; and whatis is a subdomain
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name. All together, these constitute a fully-qualified domain name (FQDN); the
addition of HTTP:// makes an FQDN a complete URL.
A generic domain is a name that defines a general category, rather than a
specific or personal instance. For example, the name of an industry, rather than
a company name. Some examples of generic names are,,
and Companies have created brands based on generic names, and
such generic domain names may be valuable.
5.3.4 Uniform Resource Locator (URL)
A Uniform Resource Locator (URL) (commonly informally referred to as
a web address is a reference to a web resource that specifies its location on
a computer network and a mechanism for retrieving it.
A URL implies the means to access an indicated resource. URLs occur
most commonly to reference web pages (http), but are also used for file transfer
(ftp), email (mailto), database access (JDBC), and many other applications.
The format combines the pre-existing system of domain names with file
path syntax,
where slashes are
separate directory and file names.
Conventions already existed where server names could be pretended to
complete file paths, preceded by a double slash ( // ).
5.4 Internet Applications
E-mail stands for electronic email. It is the most popular service provided by
the Internet. It provides the fast and efficient way to send and receive messages
through Internet. One message can be sent to many persons with a single e-mail.
Different types of files can also be sent as attachment through e-mail.
World Wide Web (WWW)
The World Wide Web is commonly known as web. It is a network of web
servers that stores web pages. The web pages are connected to each other using
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hyperlinks. The user can jump from one page to another by clicking the
hyperlinks. The web pages are accessed using web browsers. The HTTP (Hyper
Text Transfer Protocol) protocol is used for communication between browser
and web servers.
File Transfer Protocol
FTP stands for File Transfer Protocol. It is a way for transferring files
from one computer to another. The process of transferring a file from a server
(or remote computer) to local computer is called downloading. Similarly, the
process for transferring a file from local computer to the server on the Internet is
called uploading.
Different FTP client programs are available for uploading and
downloading files to and from the server. The most commonly used FTP client
programs are WS-FTP and cute FTP.
Telnet is an abbreviation for Terminal Network. It is software. It is used
to connect to a remote or host computer for accessing information. Through this
service, the user can also access information on the Internet.
When a user runs this software on their computer, it provides a prompt on
the user's computer screen. The user can access the host computer by giving
commands through this prompt. When a command is sent to the host computer,
information is accessed from host and displayed on user's computer screen. The
user's computer linked to the remote computer will act as a terminal.
Internet Relay Chat
IRC is short for Internet Relay Chat and is a popular chat service. IRC
enables users to connect to a server using a software program or web service
and communicate with each other live. For example, the Computer Hope chat
room uses an IRC server to allow its users to talk and ask computer questions
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To connect and chat with other IRC users, we must either have an IRC
client or a web interface that connects us to IRC servers. There are numerous
software IRC clients that enable users to connect and communicate to other IRC
On the Web, certain sites like Talk City or IRC networks such as
the Undernet provide servers and helps us to download an IRC client to our PC.
We can start a chat group (called a channel) or join an existing one. There
is a protocol for discovering existing chat groups and their members. Depending
on the type of network, nicknames can be reserved (registered) or just used
during the session.
Popular ongoing IRC channels are #hottub and #riskybus. A number of
channels are set up and conducted in foreign languages. The most common IRC
networks are IRCnet (mostly European), EFnet (mostly North American),
Undernet, and Dalnet. Popular IRC clients include mIRC for Windows, IRCle
for Mac OS, and irc2 (the original client) for UNIX-base operating systems.
A gopher is a menu-based information retrieval system. It is used for
retrieving files and programs on the Internet. Gopher allows access to files
found on FTP servers and web servers.
Internet provides the facility to its users to chat with people online all
over the world. Different programs like MSN Messenger, Yahoo Messenger,
AOL etc. are available for chatting on the Internet. Chat rooms allow the users
to participate in a chat on the Internet. Chat rooms are locations on the web that
provide facilities to the users to chat with each other online over the Internet.
They send messages by typing with keyboard and receive messages from other
end instantly. Some chat rooms support voice chats and video chats where
people talk with each other and see them also.
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Commerce through Internet
The smooth operation of a business depends on the efficient exchange of
information between different parts of business, between business and outside
E-commerce is nothing but business through Internet. This is a dynamic
set of technologies, applications and business process that links enterprises,
consumers and business communities through electronic interchange. Simply
the process of achieving business priorities through smart and efficient use of
Internet technology is called as E-commerce.
E-commerce is a multifaceted concept which includes the following
- Conduct of business via communication networks
- Management through electronic methods such as electronic data
interchange and automated data collection system
- Electronic transfer of funds between buyers and suppliers
- Creates interdepencies between the company and supplier & customers
related to the company
- Internet based marketing
- Intranet based information (A private network designed for information
management within an organization)
- Extranet based information (An extension of organization‘s intranet by
using WWW technology to facilitate communication with the
corporation‘s suppliers and customers.)
Various services integrated by E-commerce are
- Communications services which supports the data transfer from the
originator to the recipient
- Data management services which defines the exchange format of the
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- Security services which authenticate the source of information,
guarantee the integrity of the information received, prevent from unauthorized
users and document the acknowledgement from the recipient.
IT Implementation Trends in business
Information Technology (IT) has certainly changed the traditional
business methodology. With the advent of IT business process management and
automation was achieved with full potential thereby reducing human errors. The
following are some of the IT implementation trends in business.
To improve customer service - Business Process Management (BPM)
and automation, Customer Relationship Management (CRM), Business
Intelligence (BI), Decision Support System (DSS).
IT enabled BPM has and more scientific approach that has improved, the
turn-around time, with high processing speeds. CRM, BI and DSS are other IT
enabled business services.
CRM is to service customers, retain existing customers, integrate multiple
communication channels (mobile, e-mail, web etc) so that their customer‘s
support requests reach a common, central touch point. An e-CRM includes
Sales Force Automation (SFA), marketing applications and customer service
and support applications.
BI and DSS are the need for executives, to know about the customer,
business solutions, create right type of report for faster decision making.
IT/ITES – Business solutions are easily achieved with Information
Technology/ IT Enabled Services that applies complex data warehousing tools
to store information, data mining technologies to retrieve information. Online
training program for employees, video and web based conferencing, call centre
service, consolidated datacenter are some other ITES in business.
SCM, PLM, KM are some of the ITES in business.
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SCM – Supply Chain Management – SCM facilitates the companies to
examine their manufacturing, distribution, among multiple suppliers and
business partners.
For manufacturing customized software packages such as basic
accounting package for the accounts department, inventory management
packages for the store and separate software for production planning etc are
used. Most industries are having common ERP (Enterprise Resource Planning)
which serves as central part of business strategy and planning.
Advantages of using SCM are greater visibility into work-in-process,
cycle times, productivity, equipment utilization, inventory management,
delivery effectiveness etc.
PLM – Project Lifecycle Management – The lifecycle spans from design
of product to manufacturing it without defects. The important stages of PLM are
- Designing
- Authoring
- Manufacturing
- Product
This has to be achieved by reduced production time and cost without
compromising quality. At each stage customized software packages are used for
improving efficiency.
Typically, stakeholders of manufacturing companies are distributed
across geographies. However, the ability to come up with frequent design
changes with reduced production cycle time is very important for manufacturing
companies to stay ahead of curve. PLM provides solutions to this, which
include 3D design platforms, product design authoring, manufacturing process
creation and management, product testing etc.
KM – Knowledge Management – KM uses web technologies to distribute
their brand name, goodwill and ideas to employees and customers through
website, presentations, documentations etc. The company‘s trademarks, patents,
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potential customers, annual reports, sales figures will documented and are
analyzed for future presentations using this knowledge.
All organizations have two kinds of knowledge – explicit and tacit.
Explicit knowledge can be documented, such as the company‘s patents,
trademarks, customer lists and sales figures. Tacit knowledge is what the
employees gain over the years, after spending significant time in their respective
fields. KM is the ability to capture and utilize this tacit knowledge that is
identify, capture, share and manage the tacit knowledge in the minds of the
The easiest way of doing this is, by using web technologies. The gained
knowledge can be distributed to employees through website, chat sessions,
presentations or streaming audio/video.
Business – Intelligence, Analytics and Reengineering
ITES has extended its services in BI, BA and BPR. BI uses data mining
and web mining technologies. BA enables future predictions based on decision
support system. BPR is Business Process Reengineering that redesigns the
workflow for improving business efficiency.
BI/BA tools – Business Intelligence and Business Analytics. BI systems
can help organizations mine real time data for valuable and accurate insights.
BA is no longer a technology that only large enterprises can offer. Today, even
SME (Small to Medium scale Enterprises) can also gain from this technology,
because of high benefit. BI & BA both are meant to help the planning. But BA
is more flexible than BI. BI resembles more of typical data base operations,
where we query facts, whereas BA allows us to dig at a deeper level and model
what-if scenarios as well as optional outcomes. Example: BI – Oracle, MySQL
server, BA – SAP, IBM‘s cognos Insight.
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All ITES uses latest technologies like mobile computing and cloud
computing. Also social media like whatsapp, facebook, twitter, hike, instagram
plays important role in promoting business.
BPR – Business Process Re-engineering – It means redesigning the
workflow to make the business more efficient.
Technologies like cloud computing, mobile computing and social media
make it possible for aspiring entrepreneurs to try their ideas with minimal
E-commerce and its benefits
Placeless office/ E-marketplace – Reduces market place .Many
organizations are turning to e-commerce as a viable option for marketing and
selling the products and services. This can be done by using an e-marketplace
such as e-Bay or the company‘s own website is used.
Paperless office – Reduces paper usage. Paper and printing are
significant cost to every organization. To reduce this, most of the organizations
are having Internet/Intranet based centralized application that has digitized
workflow to move towards paperless office.
Currency less transactions /Online payment systems - Reduces currency
usage. Trend of shopping online are on a steady rise. More and more users are
now using online shopping to save time and efforts. So, for an organization it is
vital for proper payment system. For payment, several card mode systems, echeque, payment via ATM, online banking or e-banking, mobile banking etc are
The most important aspects related to any payment system are
reliability, secure, ease of use and cost effectiveness.
News Groups
Newsgroups are Internet-based discussion group, similar to a bulletin
board system (BBS), where people post messages concerning whatever topic
around which the group is organized.
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Newsgroups are typically found on USENET, a network of discussion
groups where millions of users read postings, or articles, using software called a
newsreader. Users can then make comments and ask questions in response to
the postings. Thousands of newsgroups exist, covering a wide range of topics.
Newsgroups typically fall into a few basic categories. There are newsgroups
that have to be pre-approved and cover a specific topic, and there are alternative
newsgroups that can be created by anyone and cover any topic of their
choosing. Newsgroups are also categorized as either moderated—posts have to
be approved—or immoderate.
Newsgroup names are made up of parts, separated by dots, that indicate
the topics covered in the newsgroup. The parts of the name go from least
specific to most specific. For example, the group name comp.sys.apple2
discusses computers (a general topic), systems (a computer topic), and Apple II
(a specific computer system). Some common group subjects are comp
(computers), rec (recreation), and sci (science). Other newsgroups follow a
similar order, including alternative groups, which start with alt.
Social Networking
A social networking service (also social networking site or SNS) is a
platform to build social networks or social relations among people who share
similar interests, activities, backgrounds or real-life connections. A social
network service consists of a representation of each user (often a profile), his or
her social links, and a variety of additional services such as career
services. Social network sites are web-based services that allow individuals to
create a public profile, create a list of users with whom to share connections,
and view and cross the connections within the system. Most social network
services are web-based and provide means for users to interact over the Internet.
The main types of social networking services are those that contain
category places (such as former school year or classmates), means to connect
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with friends (usually with self-description pages), and a recommendation
system linked to trust. Popular methods are Face book, Google+, LinkedIn, and
A blog (short for weblog) is a personal online journal that is frequently
updated and intended for general public consumption. Blogs are defined by their
format: a series of entries posted to a single page in reverse-chronological order.
Blogs generally represent the personality of the author or reflect the purpose of
the Web site that hosts the blog.
The author of a blog is often referred to as a blogger. People maintained
blogs long before the term was coined, but the trend gained momentum with the
introduction of automated published systems, most notably Blogger at
A videoconference is a live connection between people in different
locations for the purpose of communication, usually involving audio and often
text as well as video. At its simplest, videoconferencing provides transmission
of static images and text between two locations. At its most sophisticated, it
provides transmission of full-motion video images and high-quality audio
between multiple locations.
The tangible benefits for businesses using videoconferencing include
lower travel costs and profits gained from offering videoconferencing as an
aspect of customer service. The intangible benefits include the facilitation of
group work among geographically distant teammates and a stronger sense of
community among business contacts, both within and between companies.
Videoconferencing software is available as standard computer equipment. For
example, Microsoft's NetMeeting is included in Windows 2000.
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Online services
We can enjoy several benefits with a PC and internet connection. Some
of them are
message boards,
conferencing, blogs, micro-blogging e.g. Twitter, newsgroups, chat, ecommunities, social networking
Real Time Information - train timetables, news services, traffic reports, weather
Commerce - shopping, banking, auctions
Government - online tax returns, e-voting, applications for services (e.g.
university entry, business incorporations, land registration), revenue collection,
health services like NHS Direct
Education - VLEs, online learning, school web sites, school league tables,
online revision, simulations, online teaching
Business - video conferencing, collaborative working, business networks
Entertainment - multi-user games, radio players, sports, books
Download Services - software, upgrades, music, film
Web Storage - Google docs, Drop Box
Online mapping and route planning - Google maps, AA Route planner, RAC
route planner
5.5 E-mail address structure
E-mail allows the user to communicate information, through the internet.
An E-mail address identifies a person and the mailbox for the purpose of
exchanging messages. Most of the e-mail address contains three basic parts,
while others can be more complex.
Account Name
The first part of the email address shows the name of the account holder, or the
sender, followed by the "@ (at)" sign. It is usually the name used to log in to the
account and is also called a username.
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The name of the domain that hosts the account will follow the username and
"at" sign. If a person has a Google email account, the address would read
"[email protected]"
Domain Extension
The last letters following the domain name and the dot will be an abbreviation
of the type of organization the address originates from. A commercial domain
uses ".com," government uses ".gov," educational institutions use ".edu,"
organizations use ".org," and networks use ".net."
Country Code
If an email sender is from a foreign country, the email address may have two
letters at the end indicating which country it is coming from. This code may
replace the domain extension or be added after. For example, the United
Kingdom is .uk, Ireland is .ie, France is .fr, and Australia is .au.
The level of complexity will depend on the email server. Some organizations
and companies may add a sub-domain followed by a dot between the "at" sign
and the domain name. Others may add an extra part in the account name.
5.6 Sending and Receiving E-mail
In a desktop based client like outlook, windows live mail etc, the Figure 5.1
below shows how email is sent and received.
The email is composed on the email client (C1).
When we hit send, the email is transferred to the Email server (S1) using the
SMTP (Simple Mail Transfer Protocol).
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Figure 5.1Sending and receiving E-mail on Internet using desktop E-mail
The email server (S1) belongs to our email provider e.g.Yahoo.
The email server (S1) needs to deliver the email to the destination server (S2).
Message transfer between email servers is done using SMTP.
The destination server (S2) holds the recipients mailbox.
There are two choices that sever S1 can make:
1. It can deliver the email directly to the destination server S2.
2. It can send the Email to an Intermediate server S3.
Direct Delivery – If the sever S2 uses direct delivery then it needs to find the
email server responsible for the recipient mailbox. This it does using a DNS
lookup and MX records.
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli.
Indirect Delivery – If it chooses to use an intermediate server (S3) known as an
email forwarder then the intermediate server must then choose either a direct
delivery or to forward to another server.
Receiving the Email
The sent email will eventually be placed in a mailbox on the server S2. The
server S2 is the email server of the email provider for the recipient.
The recipient isn‘t notified that he has email. To find out if he has new email the
recipient must connect to the email server S2 and check his mailbox.
All desktop based email clients will have a default email check interval when
they check for new email, as well as a manual option (Figure 5.2)
Figure 5.2 Desktop based E-mail client options
There are two protocols used for transferring email from an email server
to a client –POP3 (Post Office Protocol) and IMAP4 (Internet Message Access
SMTP is not used for receiving email on an email client.POP3 is the
oldest protocol, IMAP4 is the newer and much better protocol, and is the
preferred option today.
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli.
The main difference between the two is that POP3 was designed to move
the email from the email server to the email client and delete it from the email
server. This means that once a POP3 client has connected to the email server it
leaves the mailbox on the server empty and the only copy of the email is now on
the email client.IMAP4 was designed to leave all email on the email server and
only copy the emails to the email client.
5.7 Search Engines
The World Wide Web is full of information. All kinds of articles, reports,
news, tables, databases, books, reviews, etc. are stored in this huge global
network. To find the most relevant resources, search engines are used to locate
and return the documents that match the specific criteria from the search query.
On a user level, the procedures are very simple. All the user has to do is
to input necessary key word of the search. In addition, most search engines offer
additional features that allow the user to narrow down the search. Such feature
is typically referred to as advanced search. With this the user can not only
indicate what the search engine must fetch, but can also specify when, what
kind, where, language, filtering and other criteria. These features are common
and they are included into every search engine.
The method that the search engines used to decide which page match with
the query is a real science. Search engines have their own technologies,
algorithms, and formulas. Generally, search engines use some parameters and
criteria to determine relevancy. Those that are widely know include the
occurrence of the search query term on the page text, the title, the meta tags, in
the liking text inside the page, in the URL address (Uniform Resource Locator),
the headings, as well as bold and italicized font, and in the text outside the site
but linking to it. Google‘s Page Rank is famous for valuing the external linking,
while MSN relies more on the actual content of the page and not the links.
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli.
Again, all search engines are unique, and have their own formulas and
algorithms, but they perform the same function; they fetch relevant results that
match the user‘s query.
In order to build up a huge database of the web-sites, search engines use
their crawlers or spiders, or bots. A crawler is an automated web-browser,
which follows every link it sees. These crawlers visit a site and all its internal
pages, gather them, and bring back to the server for index. Thus, a search engine
keeps a saved version of all indexed pages on the server; these saved pages are
referred to as cache.
Once the page is indexed, the search engine algorithms and formulas
analyze the content of the pages. The technology checks the occurrences within
the page and checks the external links from without to this page to determine
the relevancy for a certain keyword. The combination of the various criteria
gives the page a certain ranks under this keyword or key-phrase query, and then
the engine returns the results to the user.
In addition to key word search, searching methods adopted by search
engine are Boolean search, Concept search, Full text index, Fuzzy search,
Phrase search, Query-by-example search etc.
Some popular search engines are Google, Bing, Yahoo, Ask, Aol.
Meta search engines
Web Meta searchers provide a single interface that enables users to
search many different search engines, indexes and databases simultaneously.
IxQuick/StartPage, Mamma.
Special Search engines
To do academic research or purely scientific research, these Sites can be
an invaluable aid.
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli.
Google Scholar ( Google Scholar is a free
academic search engine that indexes academic information from various online
web resources.
CiteSeerx ( CiteSeerx is a digital library and an
online academic journal that offer information within the field of computer
science. It indexes academic resources through autonomous citation indexing
system. This academic database is particularly helpful for students seeking
information on computer and information sciences.
5.8 Internet and Viruses
5.8.1 Computer Virus
A VIRUS (Vital Information Resources Under Siege) is a malicious
program designed to disperse copies of itself to other computers and disrupt
those computer‘s normal operations. A computer virus usually attaches to or
inserts itself in an executable file or the boot sector (the area that contains the
first instructions executed by the computer when it is started or restarted) of a
disk. Although some viruses are merely disruptive, others can destroy or corrupt
data or cause an operating system or applications program to malfunction.
Virus is the generic term used to describe a group of destructive computer
programs. The three most common types of destructive programs are the Worm,
Trojan horse and the Logic bomb.
A worm is a program that replicates itself. It creates an image of itself
either in a file or a particular location on the disk. It also propagates itself over a
network, reproducing as it goes.
A Trojan horse program is hidden inside another, apparently useful
program. While the useful program is running, this program does something
nasty, like erase the File Allocation Table (FAT) and directory. This type of
program may be distributed through USB drive, an external disk, Internet
downloads, e-mail etc.
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli.
A Bomb is a piece of code embedded in a program or the operating
system itself that waits for a particular event to occur such as specific date.
When that event occurs, the logic bomb goes off, doing some kind of damage.
Millions of computer malware programs are known; they can be spread
via removable disk or drive, networks or Internet websites and services.
5.8.2 Internet and viruses
The Internet brings a new dimension to the virus problem. Earlier days,
viruses generally spread from system to system on physical media, often the
floppy disk. This is a fundamentally slow way for viruses to spread and they are
bad at reproduction. The Internet changes all this.
Most of the danger on the Internet currently comes from old viruses
exploiting new paths for transmission. There are basically two ways they can do
this: innocent and malicious distribution.
Innocent virus distribution
Sharing software over the Net is simple and easy; a simple mouse click
attaches a program to an e-mail, and it is just as easy to detach and run it.
People can place a program on their web page almost as simply, and this can be
downloaded by anyone anywhere. Any one of these programs could be infected.
What kinds of viruses could these practices spread? Purely boot sector
viruses are out. Parasitic file viruses work well in this environment, although
many (but no means all) users are cautious about obtaining programs from
places they do not trust.
The viruses that really win in the Internet environment are the macro
viruses. They are attached to data, not code, making them harder to avoid. An
increasing number of documents on the Net are available as Word files, for
example, with no alternative format, and Word documents are frequently
exchanged via e-mail.
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli.
The only solution here is to obtain viewer programs which read the data
in the file but ignore the macros. Such programs are available for Word and
Excel among others. Never open a file that does not trust with the application
that created it.
Malicious virus distribution
Viruses may also be spread by malicious individuals, knowingly passing
on infected programs. Virus authors and others find the Internet perfect for
giving a new virus a start in life, by means of hundreds of unsuspecting Internet
users; by infecting an attractive-looking file that then gets placed in a public
download area, the virus can spread far in a short time.
Viruses typically are programs. But that‘s not always the case. In case of
Internet actually the virus is not only a program, it also is available in other
forms also. The following are the some forms of virus through Internet.
Virus through e-mail
There have been an increasing number of hoaxes and scares stories about
email viruses in recent years.
A Virus as an E-mail Hoax
Sometimes we may receive, forward chain letter, a virus warning, or the
email of a desperate parent whose child needed an organ donation?,
probably fell for a hoax and helped to spread it.
In this case the virus is the e-mail itself, although it‘s not really an
infection. The damage, however, is the same as with other viruses: clogging up
of inboxes and mail servers. E-mail viruses generally cause a waste of time,
resources, and energy.
Don‘t forward hoax email, unless we‘re sure it‘s genuine. Hoax-Slayer is
a good resource to get informed about email hoaxes and eventually verify the
credibility of an e-mail we received.
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli.
A Virus in an E-mail Attachment
While forwarding an e-mail doesn‘t cause any major damage, an
infection with a ―real‖ computer virus is a lot more critical. There are
―harmless‖ variants that just forward themselves to the contacts. However, a
virus may also be programmed for example, to destroy specific files on our
Most viruses are delivered through an e-mail attachment. Attachments
that contain viruses are either executable programs (file types: .com, .exe, .vbs,
.zip, .scr, .dll, .pif, .js) or macro viruses (file types: .doc, .dot, .xls, .xlt). The
safest way to avoid them is to not open e-mail attachments.
It is safe to open Word documents in alternative programs that don‘t
support macros, such as WordPad or Open Office.
Simply downloading and reading the email will not do any harm. As long
as the attachment is not opened, the virus won‘t hatch. If we don‘t know the
sender and if the e-mail text is suspicious, just delete the e-mail along with the
A Virus in the Email Body
Sometimes the malicious content can be found in the body of an e-mail.
Today, HTML is a common element of e-mails as it is used to embed pictures
and links. However, HTML can also be used to embed scripts that execute
automatically and subsequently infect our computer with a virus. That‘s why
many mail programs, by default, block HTML and make click a button to
display content of trustworthy sources.
Also, URLs can be a virus in disguise. We may see a harmless link that
either leads to a website that executes a malicious script or links to a completely
different URL where we automatically download a self-executing virus. The
same rule as for attachments applies: never view or access links from suspicious
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli.
Macro viruses
Macro viruses have become common in Internet. Most of these viruses
are written in the scripting languages for Microsoft programs such
as Word and Excel and spread throughout Microsoft Office by infecting
documents and spreadsheets. Since Word and Excel were also available for Mac
OS, most could also spread to Macintosh computers. Although most of these
viruses did not have the ability to send infected email messages, those viruses
which did take advantage of the Microsoft Outlook COM interface
A virus may also send a web address link as an instant message to all the
contacts on an infected machine. If the recipient, thinking the link is from a
friend (a trusted source) follows the link to the website, the virus hosted at the
site may be able to infect this new computer and continue propagating.
Viruses from Face book
There are a variety of viruses that can be obtained from using Face book.
One kind is a worm. It can copy itself within our computer as well as from one
machine to another. A worm infects the computer as well as the Internet and
slows things down significantly.
Zeus is a Trojan virus that gets into the computer without our knowledge.
It remains dormant until we access our bank account, and then it has access to
our log-in information and is able to steal from the account.
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli.
Text Book:
Computers – Basics to Advancements, Dr.P.Velmani & Dr.V.Lakshmi Praba, 1/e, Chess
Educational Publishers, Chennai.
Reference Books:
1. Introduction to Computer Science, ITL, Education Solutions Limited, 2/e, Pearson
2. Introduction to Computers, Peter Norton, 7/e, TMH.
Prepared by
Assistant Professor, Department of Computer Science,
The M.D.T.Hindu College, Tirunelveli.
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli.
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