Compendium for computer application

INTRODUCTION TO
MICROCOMPUTER AND
APPLICATIONS
(CIT 100)
Contents
INTRODUCTION TO MICROCOMPUTER AND APPLICATIONS ....................................................1
(CIT 100)................................................................................................................................. 1
Contents................................................................................................................................. 1
CHAPTER ONE: INTRODUCTION TO COMPUTER.......................................................................2
CHAPTER TWO: COMPUTER SOFTWARE................................................................................43
CHAPTER THREE: WORD PROCESSING SOFTWARE...............................................................63
CHAPTER FOUR: ELECTRONIC SPREADSHEET SOFTWARE.....................................................80
CHAPTER FIVE: COMPUTER NETWORKING..........................................................................102
CHAPTER SIX: COMPUTER VIRUSES.....................................................................................120
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CHAPTER ONE: INTRODUCTION TO COMPUTER
We are living in an information age dependent upon digital information. Digital
information is an electronic information result of computer processing. Every
type of job relies upon getting information, using it, managing it, and relaying
information to others. Computers enable the efficient processing and storage of
such information.
Do not think of a computer merely as the machine with the keyboard and the
mouse, although that might be true for some types of computers. Embedded
computers may be inside your household appliances, the Video Cassette
Recording (VCR), the automobile, planes, trains, power plants, water
purification plants, calculators, and even inside a few toys. These embedded
computers are very small. They affect our lives each day. They are all around
us; even modern traffic lights operate with computers. Think of additional ways
in which computers affect our lives each day. Be in any organization, office,
factory or institution, you can find people making use of computer for different
purposes. For example in offices, computers are used for preparing letters,
documents and reports. In hotels, computers are used for advance booking of
rooms, preparing bills and providing inquiry services. In railways, computers
are used for rail reservation, printing of tickets and preparation of reservation
charts. Doctors use computers for diagnosing illness and treatment of deceases.
Architects use them for map designing and city planning. In meteorology
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department, computers are used for weather forecasting. In short you can say
that there is hardly in all fields now, in which computers are not being used.
Computer is electronic equipment which is used for automating manual tasks.
Using computer you can perform many tasks quickly, effectively and with less
error. It is made by two main components namely Hardware and Software.
The former is said to be the physical component that you can see and touch
while the later is the set of instruction that makes the hardware to perform
tasks.
1.1 Characteristics of Computer
Following are the characteristics of computer:
1. Computers are basically dumb devices. They cannot perform any function on
their own. For doing anything on computer, you have to give instructions to
them. Generally these instructions are written in computer language and are
given from the keyboard.
2. Computer performs the tasks according to the instructions provided by the
user. In other words, you can say that the correctness of output depends upon
the correctness of the data and the instructions provided by the user. For
example, if you add two numbers 70 and 30, the result could be 40 in case you
have given wrong instruction i.e. subtraction instead of addition.
3. The speed, with which a computer performs a task is much faster than
manual. As a result of which, computers are widely used for performing those
tasks, in which speed is of prime importance.
4. Computer can perform a task with the same speed for several days without
getting tired. This is not possible in case of manual activities. Human beings
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get tired after sometime and the chances of making mistakes start getting high
as the time passes by. So you can say that computers are capable of performing
error free tasks efficiently for the duration, which is beyond human capabilities.
1.2 Computer generations
Thousands of different computers have been designed and built during the
evolution of the modern digital computer. Each of these computers has been
classified into generations. This section tries to highlight the computer
generations.
First Generation - 1940-1956
• The first computers used vacuum tubes for circuitry and magnetic drums
for memory.
• Were often enormous, taking up entire rooms.
• Generated a lot of heat, because they were very using a great deal of
electricity, which was often the cause of malfunctions.
• First generation computers relied on machine language to perform
operations they solved only one problem at a time.
Second Generation - 1956-1963
• Transistors replaced vacuum tubes, Transistor is a device composed of
semiconductor material that amplifies a signal or opens or closes a circuit.
• The transistor was invented in 1947 but did not see widespread use in
computers until the late 50s. The transistor was far superior to the vacuum
tube,
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• This technology allowed computers to become smaller, faster, cheaper,
more energy-efficient and more reliable than their first-generation
predecessors.
• Though the transistor still generated a great deal of heat that subjected the
computer to damage, it was a vast improvement over the vacuum tube.
• Second-generation computers still relied on punched cards for input and
printouts for output.
• Second-generation computers moved from cryptic binary machine
language to symbolic, or assembly languages, which allowed
programmers to specify instructions in words.
• High-level programming languages were also being developed at this
time, such as early versions of COBOL and FORTRAN.
• These were also the first computers that stored their instructions in their
memory, which moved from a magnetic drum to magnetic core
technology.
• The first computers of this generation were developed for the atomic
energy industry.
Third Generation - 1964-1971
• The development of the integrated circuit was the hallmark of the third
generation of computers. Transistors were miniaturized and placed on
silicon chips, called semiconductors, which drastically increased the
speed and efficiency of computers.
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• Users interacted with third generation computers through keyboards and
monitors and interfaced with an operating system.
• Used to run different applications at one time with a central program that
monitored the memory
• Computers for the first time became accessible to a mass audience
because they were smaller and cheaper than their predecessors.
Fourth Generation - 1971-1980s
• The microprocessor brought the fourth generation of computers, as
thousands of integrated circuits we rebuilt onto a single silicon chip.
• A silicon chip that contains a CPU. In the world of personal computers,
the terms microprocessor and CPU are used interchangeably. At the heart
of all personal computers and most workstations sits a microprocessor.
Microprocessors also control the logic of almost all digital devices, from
clock radios to fuel-injection systems for automobiles.
• Three basic characteristics differentiate microprocessors:
o Instruction Set: The set of instructions that the microprocessor can
execute.
o Bandwidth: The number of bits processed in a single instruction.
o Clock Speed: Given in megahertz (MHz), the clock speed
determines how many instructions per second the processor can
execute.
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• In both cases, the higher the value, the more powerful the CPU. For
example, a 32-bit microprocessor that runs at 50MHz is more powerful
than a 16-bit microprocessor that runs at 25MHz.
• What in the first generation filled an entire room could now fit in the
palm of the hand. The Intel 4004chip, developed in 1971, located all the
components of the computer - from the central processing unit and
memory to input/output controls - on a single chip.
Fifth Generation (1985 - Present)
• The changes that have occurred since 1985 are plentiful. Computers have
gotten tinier, more reliable, and many times faster.
• Computers are mostly built using components from many different
corporations. For this reason, it is easier to focus on specific component
advancements.
• Intel and AMD are the main computer processor companies in the world
today and are constant rivals.
• There are many different personal computer companies that usually sell
their hardware with a Microsoft Windows operating system preinstalled.
Apple has a wide line of hardware and software as well.
• Computer graphics have gotten very powerful and are able to display full
three dimensional graphics at high resolution.
• Nvidia and ATI are two companies in constant battle with one another to
be the computer graphics hardware king.
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1.3 Types of Computers
Computers can be classified into various categories, on the basis of their sizes.
When we say, size of the computer, it refers to multiple factors like, size of the
memory, number of terminals that can be connected to the computer, size of
the hard disk, type of processor used in the computer etc.
Computers are generally classified into following categories:
1. Microcomputers
2. Minicomputers
3. Mainframe computers
4. Supercomputers
1.3.1Micro Computers
Microcomputer is the smallest category of computers, in which single
microchip is used for two basic units i.e. ALU and Control Unit. This
microchip is often referred to as microprocessor. Microcomputers are further
classified into following categories:
1. Personal computers
2. Laptop computers
Personal Computers (PC)
Computers that we commonly see these days in offices, hotels, restaurants etc.
are examples of Personal Computer. In short they are called PC. Outward
appearance of PC is shown in figure 1.0. PC mainly comprise of four units i.e.
chassis (also called CPU box), keyboard, VDU and mouse. Only one person
can work on it at a time. This is the reason why PCs are called single user
computers. Originally PCs were designed and manufactured by IBM. Later,as
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they became popular, other manufacturers also started manufacturing similar
type of computers called IBM clones.
Figure 1.0 Personal computer
Laptop Computers
Laptop computers also fall into the category of microcomputers. Their
capabilities are the same as that of a PC. A laptop computer is shown in figure
1.1. Laptop computers look like a briefcase. Upper panel of the briefcase
comprises of LCD screen. Lower panel contains keyboard and mouse
arrangement. Other components and circuitry remains packed inside the
briefcase. Laptop computers are deliberately designed to be light in weight.
They run on chargeable battery, which resides inside. Due to their size, weight
and independence from power (for two to three hours) people carry them while
traveling in car, train or airplane and work on them.
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Figure 1.1 Laptop Computer
1.3.2 Minicomputers
Minicomputers are relatively larger and faster computers. They support multi
user environment. They are generally used for automating those applications,
which are large in size, require fast processing capabilities and demand for
resource sharing among multiple users. Main characteristics of Minicomputers
are described below:
1. They are built, using high performance and high capability processors.
2. Memory size, in such type of computers is generally very large.
3. They support multiple terminals connectivity, which may range from 2
to 128.
4. Large capacity disks are used in multiple numbers so that the data and
programs of all the users could be put on-line.
5. They provide facility to connect multiple printers.
6. They possess the capability of performing computer network related
operations.
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1.3.3 Mainframes
Mainframes fall into next higher category of computers. Their internal
architecture and circuitry remains different from Minicomputers. They use
specially designed proprietary circuits instead of just single microprocessor as
their CPU. Their circuitry promotes higher connectivity, faster throughputs and
large data processing capabilities.
Due to proprietary circuitry, Mainframes become quite big in size and provide
facility for connecting Minicomputers and microcomputers with them. Few
characteristics of Mainframes are listed below:
1. They possess the capability of addressing larger memory sizes than that
of Minicomputers.
2. They also support larger capacity disks like optical disks etc.
3. Their terminal connectivity can go as high as 256 or beyond.
4. They possess large number of application libraries that provide great
help to developers in developing useful applications.
DEC 20, IBM 370 etc. are the examples of few mainframes. IBM (USA) is the
largest manufacturer of Mainframes.
1.3.4 Supercomputers
Supercomputer is the largest category of computers. They use multiple CPUs
for processing the data and executing the instructions. While performing a task
through Supercomputer, the complete task gets divided into multiple
independent tasks. Each CPU performs individual task and completes it in
parallel. This methodology of processing is called parallel processing.
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Due to parallel processing, Supercomputers are capable of processing large
volumes of data at very fast speed. They process multi million to few trillion
commands per second. Applications like weather forecasting, nuclear weapon
design, projection system modeling, aero modeling etc. which require
tremendous processing capabilities, can be very well executed on
Supercomputers. CRAY, XMP 24 and NEC 500 are few examples of
Supercomputer.
1.4 Computer operation
Generally Computer performs four general operations which are:
 Input - Entry of raw data; for example, typing names and addresses on
a keyboard or transmitting a picture from a digital camera.
 Processing - Manipulation of the raw data to produce useful
information, the key purpose of a computer; for example, sorting or
indexing the names and addresses or adding effects to the picture.
 Output - is the result of a computer process. Output may be
viewed on a monitor screen, heard through speakers, printed on
printers, and so forth.
 Storage - Retention of the data until it is needed; for example, filing
names and addresses in a database or archiving the picture in an online
library. With a basic understanding of these key functions, the role of
each of the components of a PC becomes much clearer.
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Each of this operation is performed by specific unit in the computer. This
section will give an explanation and organization of each unit of the computer.
Before we discuss each unit let us define the term hardware as part of computer
system. The term computer hardware refers to the physical components of a
computer, i.e. all the components that you can physically see and touch
namely: keyboards, CPU, monitors, drives (hard disk, CD, DVD, floppy,
optical, tape, etc...), mouse, printers, modems, scanners, digital cameras and
cards (sound, color, video ). Computer hardware is an integral part embedded
in all modern day automobiles, microwave ovens, electrocardiograph
machines, compact disc players, and other devices. In fact computer hardware
without software is useless; it is the software that instructs it to perform a
particular task
As you know, computer is an electronic device, it comprises of many units.
These units work in coordination with each other to perform the given task.
Block diagram of computer is shown in figure 1.2. Referring to this figure we
note that computer comprises of following units:
1. Input Unit
2. Central Processing Unit
(a) Memory Unit
(b) ALU
(c) Control Unit
3. Output Unit
4. Input/Output Unit
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Therefore a computer system is defined as a device that accepts input,
processes, stores, and produces output.
Physically the units exist in the form of electronic devices which can be seen
and touched. Generally a computer system is made up by Hardware and
Software. Each unit performs its own function, in coordination with other
devices to perform the given task. What is the role of each unit and in what
form do they physically exist, will be explained in the following subsections.
Figure 1.2 Computer units
1.4.1 Input Unit
Computer receives data from user through input unit. An input device is any
hardware component that allows a computer user to transfer information or
data, programs, commands, and user responses into a computer system. In
general the role of input unit in computer is to provide means for supplying
data or instructions to the computer. In other words, you can say that what you
supply to the computer for processing is supplied through input unit. For
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example, if you wish to calculate simple interest on Tsh. 100,000, at 17% for
10 years then the data 100,000, 17%, 10 years etc. and the instructions for
calculating the simple interest will have to be given to the computer, through
input unit.
All those devices, that works in entering information to the computer falls in
this unit (input unit) Few commonly used input devices that can be found
attached with almost every computer, includes keyboard, mouse, and CD-Rom
drive. Others are scanner, digital camera, joy stick, microphones etc. The
primary input devices are discussed here under.
Computer Keyboard
The keyboard is the standard device used to enter information into the
computer system. It looks and operates much like a standard typewriter
keyboard and includes the 26 letters of the alphabet, the 10 digits used for
numbers, and some special characters. However, a computer keyboard had
many additional keys that allow it to do many special things a regular
typewriter cannot do. The keys in a computer are classified in the following
categories; Alphabet keys, Number keys, Special character keys, Function
keys, Cursor keys and Action keys.
Alphabet keys
Alphabet keys have alphabets, from A to Z, written on them. By pressing these
keys, you can type alphabets, words, sentences etc. in lower case. For example,
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when you press 'A' key, 'a' gets typed. To type the alphabet in upper case, you
need to press Shift key along with the alphabet key. For example, if you press
'A' key along with Shift key, letter 'A' gets typed.
Number keys
Number keys have digits, from 0 to 9, written on them. These keys are used for
typing the numbers. Note that each number key also has a special character
written just above the number. To type this character, you will have to press the
number key along with the Shift key. For example, number 5 key has % sign
marked on it. When you press number 5 key, 5 will get typed. If you pres the
combination of same key and Shift key ‘%’ sign will get typed.
Special character keys
Few keys of the keyboard have special characters like semicolon (;), comma
(,), dot (.) etc. marked on them. Such keys are called special character keys.
When you press special character key, character marked on it gets typed at
current cursor position.
Function keys
There are 12 function keys present on the keyboard. They are named as F1, F2,
F3 …..F12. When you press these keys they perform special functions
depending on which program your working with.
Cursor keys
Four cursor keys are there on the keyboard. They are marked with arrows on
them, pointing in four different directions. Using cursor keys, you can move
the cursor from one place to another.
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Action keys
Keyboard has many action keys. When you press an action key, a special event
takes place. Most commonly used action keys of the keyboard are described
below.
Caps Lock Key: When you press this key, capital lock becomes on. When you
press an alphabet key, while caps lock is on, the letter written on it gets typed
in upper case.
Shift key: Always this key is pressed in combination with other keys. When you
press this key along with number key then the symbol written on upper part of
the key gets typed. When you press Shift key along with alphabet key then the
alphabet gets typed in upper case.
Ctrl key: The Control (Crtl) key works like the Alt key. It is always used in
combination with some other key.
Esc key: The Escape (Esc) key is used to escape or leave some function you
have selected. The Escape key is always used by itself. Currently on-going
activity gets cancelled when this key is pressed.
Page Keys: There are two page keys on the keyboard, named as PgDn (i.e.
Page Down) and PgUp (i.e. Page Up). When you press PgUp key, previous
page gets displayed on the screen. When you press PgDn key, next page gets
displayed on the screen.
Enter key: The Enter key is typically used to end a paragraph when working in
most application programs or to execute a command, also it used as okay tool.
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Tab key: The Tab key is typically used to move the insertion point across the
screen to the next tab stop, in the same manner as a tab key on a typewriter.
Backspace key: The Backspace key, located directly above the Enter key,
deletes the character to the left of the insertion point.
Delete key: The Delete key, located to the right of the Enter key, deletes the
character to the right of the insertion point.
Insert Key: This key is used to insert characters in between the two characters,
which have already been typed.
All the keys on the keyboard are auto-repeat keys. This means that if you hold
the key down, the character or function that the key performs will be repeated
as long as the key is held down.
The Mouse
Another kind of input device that is often used with a computer is a mouse.
This device is shaped a little like a real mouse. In fact, the cable that connects it
to the computer looks a little like the tail of a real mouse However currently
there are wireless mouse which does not have the cable connect to the
computer system. Mouse is a pointing device that allows user to point to a
specific position on the screen. It has two or three buttons on top for
selecting/executing different operations the figure 1.3 shows the picture of a
computer mouse.
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Figure 1.3 Computer Mouse
Pressing buttons of mouse is known as clicking of mouse. The mouse is placed
on flat surface and moved around to move its controlling arrow on screen. The
arrow showing the position of mouse on screen is known as mouse pointer as
shown in figure 1.3. Left button of mouse is used execute the operation
associated with it. Right button/Middle buttons are associated with special
operations in different situations. In old technology mouse has a round ball
under the bottom that rolls and turns two wheels which control the direction of
the pointer on the screen while the currently mouse uses an optical system to
track the movement of the mouse.
Figure 1.4 Mouse Pointer
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Note: It is important to clean the mouse periodically, particularly if it becomes
sluggish. A ball type mouse has a small circular panel that can be opened,
allowing you to remove the ball. Lint can be removed carefully with a tooth
pick or tweezers and the ball can be washed with mild detergent. A build up
will accumulate on the small wheels in the mouse. Use a small instrument or
finger nail to scrape it off taking care not to scratch the wheels. Track balls can
be cleaned much like a mouse and touch-pad can be wiped with a clean, damp
cloth. An optical mouse can accumulate material from the surface that it is in
contact with which can be removed with a finger nail or small instrument.
What is the mouse and its pointer used for?
The mouse and its pointer can be used to do many things. Sometimes when you
turn on your computer, there you can use your mouse to point to one of the
program you want to use from the start menu.
Sometimes when you turn your computer screen on, you see a series of pictures
called icons. A popular program with icons is Windows. You can use the mouse
to choose one of these pictures to run the program being presented. Usually,
picking a picture allows you to start a program or do something within a
program.
How do you use the computer mouse?
By moving a mouse with your hand, you can make the pointer move around a
computer screen until you are ready to point at an object. Usually you will find
that a computer mouse has two/three buttons. The button on the left is the one
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you will most often push. Once you have the arrow pointing at the object you
wish to pick, you can click the button ones (single click) or two times (double
click) and will open whatever you are pointing at.
You can also move an object across the screen with your mouse. This is called
dragging. To drag an object across the screen, point at the object, click and
hold down the mouse button, and move the mouse to a new place on the screen
and release the button.
Note: You can set the mouse buttons according to your wishes but the above
explanation is the default setting of the mouse especially for the computer with
windows system.
CD-ROM Drive
CD is acronym for Compact Disk. It works as a medium for storing data or
instructions. It looks like circular plastic disk. Huge amount of data can be
stored on CD. For example, single CD can hold personal data of all the students
studying in a college.
CD-ROM drive is an input unit that reads data from CD. As the name indicates,
CD-ROM (Compact Disk Read Only Memory) can only read the data from
CD, it cannot write on it. CD and CD-ROM drive are shown in figure 1.5.
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Figure 1.5 Computer CD and CD-ROM drive
Some Other input devices are enlisted below:
Device Identification Usage
Joy Stick It is a device used to control cursor
on screen. Normally it is used in
Games and specially designed
simulation software.
Light Pen It is a device used for drawing
pictures and for directly controlling
screen operations.
Microphon
e
It is a device used to accept audio
inputs from the user.
Scanner It is a device used to capture digital
images of printed documents,
graphics or other printed media.
Touch
Screens
It is a display device, which is
touch-sensitive and allows user to
interact with the computer system
by touching an area on the screen.
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Bar Code
Reader
It is used to accept barcode inputs.
A barcode is a series of vertical bars
representing numbers and alphabets
printed on product labels. One must
have noticed all standard items like
perfumes, greeting cards, books,
cassettes available in the market
have similar lines as shown in the
figure, known as bar codes. These
can be read with the help of bar
code readers.
Web
Camera
It is an easy to connect low
resolution digital camera normally
employed for transfer of images on
the web-based conferencing.
Digital
Camera
It is a high-resolution camera, which
captures images and stores them in
digital format. It has provision to
connect to the computer using
special computer communication
cables (such as USB cables)
1.4.2 Central Processing Unit
Refer figure 1.2 and note that three units which are; Memory, ALU and Control
Unit put together are referred to as Central Processing Unit or CPU in short.
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The CPU, a small electronic circuit chip, is the heart of the computer system
and is the device that allows the machine to perform its complex mathematical
and logic functions. The CPU is considered the “brains” of the computer
system. Although it is not important to know how the CPU works in order to be
able to use the personal computer, it is important to know that it is a major part
of the machine. Role of each unit is explained below.
Memory
Memory holds data, instruction or results temporarily. For example, when you
give instructions to the computer to compute simple interest on Tsh. 1,000,000,
@ 10% for 3 years, this data and instructions can be entered into computer
from any of the input or Input/output devices and get stored in memory.
Similarly result (simple interest in this example) also gets stored in memory. In
other words, you can say that the unit, which holds data, instructions or results
in it, is called memory. The data being processed in a computer needs to be
stored in memory for references. Computer has two types of Memory namely
Primary and Secondary memory.
Primary memory
That memory, which is utilized by the computer for its internal functioning, is
called primary memory. Since it plays an important role in internal functioning
of computer hence it is often referred to as internal memory.
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This is the memory that can be directly accessed by the CPU which constantly
interacts with it, retrieves data stored therein, goes through instructions and
execute them as per the requirements. All the information, data and application
are loaded there in uniform manner. It is used to store the information
(programs and data) that the computer is currently using i.e. the data or
program that is being processed by the CPU are stored in this memory. In other
words the CPU directly stores and retrieves information from it. Primary
memory is further categorized into two categories:
1. Read Only Memory (ROM)
2. Random Access Memory (RAM)
Read Only Memory (ROM)
ROM- is an integrated circuit programmed with data that holds instructions for
starting up the computer. Data stored in ROM is non volatile that is; will not
get lost when powered off. These data cannot be changed until a special
operation is done to change. Using special devices, such as ROM programmer,
instructions are written in it. Once instructions are written in it, it is put inside
the computer. As and when required, computer reads instructions from it. Since
data can only be read from it hence it is called Read Only Memory or ROM in
short. ROM physically exists in the form of blank electronic chip, in which
programs or data are written, using special devices. Those ROMs, in which
data once written, cannot be erased by any means are called Programmable
Read Only Memory or PROM in short. Other type of ROM, in which data is
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written or erased, using ultraviolet rays is called Erasable Programmable Read
Only Memory or EPROM in short.
Random Access Memory (RAM)
RAM – is the temporary storage in which a CPU can read and write
information on it. In some text this memory is called read and write memory
(RWM) but RAM is the most adapted and well known terminology worldwide.
It stores the information that currently being processed by the computer. This
memory is accessed by CPU, in random fashion. That means any location of
this memory can be accessed by the CPU to either read information from it, or
to store information in it and nothing else.
RAM is temporary/volatile memory this is due to the fact that information
stored in get lost when the computer is switched off (or when power fails e.g. if
you pull out the power lead). Therefore there is need for permanent or long
term storage which is also referred to as secondary storage or auxiliary storage
(secondary storage unit).
Figure 1.6 random access memory (ram) for desktop and laptop computer.
The Arithmetic/Logical Unit (ALU)
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This unit performs arithmetic and logical calculations in computer. Recall that
calculations like, addition, subtraction, multiplication division etc. fall into the
category of arithmetic calculations. Operations like a>b, c>=d etc. are logical
operations. In computer terminology, the activity of performing arithmetic and
logical calculations is called processing. In other words it can be said that in
computer ALU performs data processing.
The Control Unit
While computer functions, data moves from one unit to another unit. For
example, when you give input to computer, data and instructions move from
input unit to memory. When data is processed, it moves from memory to ALU.
Similarly when processing is over, results move from ALU to memory and
memory to output unit. Now the question is which part of computer organizes
data movement within the computer? Well, Control Unit is the main unit,
which performs traffic police like task. It ensures movement of right data from
right source, to right destination at right time so that all the units of computer
perform their functions in coordination with each other.
1.4.3 Output Unit
Once a computer has processed information, it needs to send the information
back to the computer user (the person using the computer). A computer does
this through output devices. These are device used to provide the processed
data from the computer to the user. One of the most frequently used output
devices is a video monitor (visual display unit) and printer. Other devices
include sound board and speakers, Modems etc.
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Computer Monitor
The VDU looks very similar to a television set. The types of information that
can be displayed on it include words, pictures, tables, numbers, and graphs,
Videos etc. it display the contents that are being typed through keyboard as
well as the processed data. The size of a video monitor is measured by the
distance diagonally from one corner of the screen to the opposite corner of the
screen. Commonly Video monitors can range in size from 14"-21" (35 cm-52.5
cm) but larger size exists as well. Monitors have their own on/off switches and
usually must be turned on and off separately from the computer. The figure 5
below illustrates the VDU.
Figure 1.7. VDU
Printer
Another output device which is frequently used with a computer is the printer.
Once a computer user has created something on a computer, such as a story or
a report, he/she can display it on his/her video screen. The printer allows the
computer user to print out a "typed" or "hard’ copy of exactly what is on the
screen. Different types of printers print differently. Their quality and speed of
printing differ from each other. Following are different types of printers, which
are being commonly used these days:
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1. Dot Matrix Printer
2. Inkjet Printer
3. Laser Printer
1. Dot Matrix Printer
This printer also strikes an inked ribbon to create letters. These letters are made
up of many tiny inked dots. These printers drive their name "Dot Matrix" from
the fact that they print the characters making dots. Pins of the printer print these
dots so close to each other that the gap between them is hardly visible. Viewer
gets an impression of full continuity. These printers are versatile printers and
are capable of printing not only text, but up to some extent graphics also.
2. Ink jet printer
For printing the characters and drawings, inkjet printers make use of colored
inks. They use Cyan, Magenta, Yellow and Black inks. Using these four basic
colors, inkjet printers generate all other colors. This type of printer shoots out
small dots of ink onto the paper. These printers are very popular due to their
high quality and low cost.
3. Laser PrinterLaser printers use a laser beam to create an image that is
transferred to paper. The laser printer does not use a ribbon like the dot-matrix
printers. These are high quality, high speed and high cost printers. In such type
of printers, printing is done, using laser beam and black magnetic powder,
called Toner. The printing process with laser printers is similar to that of the
process involved in a photocopy machine.
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Figure 1.8 Printer Images
Sound Boards and Audio Speakers
Some computer programs such as video games and multimedia programs have
sound effects built into them. A type of output device that allows a computer to
produce the sounds of these programs is called a sound board. A sound board
is an electronic circuit board, located inside the computer, that can produce
music and high quality sounds.
Many sound boards are able to be connected to a pair of small external audio
speakers or even a set of larger home stereo speakers. This allows a computer
user to hear the very realistic sound effects of certain video games or
multimedia presentations. These sounds include the sound of car engines,
explosions, etc. The sound boards and audio speakers also allow a computer
user to play music through his/her computer. In some instances, speech itself
can be played through the speakers.
The Modem
The word modem is a short form for modulator demodulator. It is a special
communication device that is able to allow one computer to talk to another
computer via telephone lines. It is similar to two friends talking to one another
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on the telephone. Since the modem allows the computer to both send and
receive information, it is called an input/output device.
Some modems are located inside computers while other modems are located
outside computers. Those located inside are called internal modems. Those
located outside the computer are called external modems. In order to work,
modems require special computer software called a communication program.
Since a modem allows for the communication of information via telephone
lines, it is also referred to as a telecommunication device. Different modems
send and receive information at different speeds
1.5 Secondary memory (Auxiliary storage)
As information in RAM get lost when the computer is switched off (or when
power fails e.g. if you pull out the power lead!) then there is therefore a
requirement for permanent or long term storage of all data/information that we
will need in the future. This permanent storage is referred to as secondary
storage or auxiliary storage
It stores the data permanently unless it is erased; it is very slow compared to
primary memory and also very cheap. They are found in different sizes from
megabyte (MB) to terabyte (TB) this means the auxiliary storage can store
huge amount of data. The secondary memory devices are usually available in
the form of magnetic disk, optical disk, Pen drive (i.e. Mass storage devices),
and memory chips. In the following we will discuss some of these devices
1.5.1 Magnetic disk
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Magnetic storage and magnetic recording are terms from engineering referring
to the storage of data on a magnetized medium. Magnetic storage uses different
patterns of magnetization in a magnetizable material to store data and is a form
of non-volatile memory. The information is accessed using one or more
read/write heads. Magnetic storage media, primarily hard disks, are widely
used to store computer data as well as audio and video signals. Other examples
of magnetic storage media include floppy disks, magnetic recording tape, and
magnetic stripes on credit cards.
The hard disk
Most computers have a permanent storage device inside them called a hard
disk drive. Sometimes they are also called a hard drive. This storage device
contains rotating disks where data or programs are stored magnetically. The
amount of information that can be saved on the hard drive is dependent on its
size. The size of the hard drive, like a computer’s temporary memory (RAM),
is usually described in megabytes, Gigabyte, Terabyte. One advantage of a hard
drive is that much more information can be saved on the disks of the hard drive
than on a disk of a floppy disk drive.
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Figure 1.9 Hard disk drive
Floppy Disk
This is the former technology used for data storage and transfer from one
location to another. The floppy disk drive allows a computer user to save data
and programs on removable floppy disks or diskettes. There are two sizes of
floppy disks drives. One kind can receive 3.5" disks, while a second type,
which is rarely used anymore, works with 5.25" disks. Although the disks that
go into a floppy disk drive do not hold as much information as a typical hard
drive, these disks used to offer the advantage of being very portable. This
technology have been phased out in favor of the USB flash drive which can
perform all the work which previously was done by using the Floppy disk drive
with more advantage of storing more data, portability, faster and cheap. Until
approximately 2005, most desktop and laptop computers were supplied with
floppy disk drives, but floppy disk drives have been abandoned in favor of
USB ports.
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Figure 1.10(a) Floppy disk Figure 1.10(b). Floppy
disk drive
1.5.2 Optical Disk
An optical disc is a flat piece of circular polycarbonate plastic containing a
non-volatile recording medium that stores digital information. Data is then
accessed with a laser diode illuminating on its recording medium. To date,
many forms of optical disc have been developed. Each generally enjoys a span
of popularity of use before newer discs with greater capacity and capability are
introduced into the market. Nearing obsolete media includes Laser disc and
Video CD (VCD) while trendy media such a CD (compact disc), CD-R, CD-
RW, DVD-R, DVD-RW continue to thrive in our world of digital data and
storage.
CD-R (Compact Disc-Recordable)
 Compact disc that is recordable
 Record your own items such as text, graphics, and audio onto the CD
 You can write on each part only one time
 You cannot erase the contents of the disc
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 Can be read by most CD-ROM drives
CD-RW (Compact Disc-Rewritable)
 A compact disc that is rewrite able
 Erasable disc that you can write on multiple times
 Originally called an erasable CD
 Overcomes the major disadvantage of CD-R discs which can be written
on only once
 Acts like a floppy or hard disc allowing you to write and rewrite data,
instructions, and information onto it multiple times
DVD (Digital Versatile/Video Disc)
 A very high capacity disc capable of storing 4.7 to 17 GB
 Uses a new technology that can be used to store large amounts of text and
video
 Quality and storage capacity are far greater than a CD-ROM
 DVD-ROM drive or DVD player is needed to read a DVD-ROM - these
drives can also read CD-ROMs
1.5.3 USB Flash drive
A USB flash drive consists of a flash memory data storage device integrated
with a USB (Universal Serial Bus) interface. USB flash drives are typically
removable and rewritable, and physically much smaller than a former
technology floppy disk which have been abandoned. Most weigh less than 30g
with high storage capacity and cheap.
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USB flash drives are often used for the same purposes for which floppy disks
or CD-ROMs were used. They are smaller, faster, have thousands of times
more capacity, and are more durable and reliable because of their lack of
moving parts. Until approximately 2005, most desktop and laptop computers
were supplied with floppy disk drives, but floppy disk drives have been
abandoned in favor of USB ports.
USB Flash drives use the USB mass storage standard, supported natively by
modern operating systems such as Linux, Mac OS X, Windows, and other
Unix-like systems. USB drives with USB 2.0 support can store more data and
transfer faster than a much larger optical disc drives like CD-RW or DVD-RW
drives and can be read by many other systems such as the PlayStation 3, DVD
players, TV sets and in some upcoming mobile Smartphone.
Figure 1.11 USB Flash Drive
1.6 Inside the Computer system Unit
The system unit is the cabinet that contains many of the computers’ working
components including CPU, RAM, HDD, etc as shown in figure 1.12 below.
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Figure 1.12 Inside computer box
1.7.1 PC ports
As defined above computer port is where a physical connection of the devices
is made. There different computer port with different function as has shown in
figure 1.13 below followed by the explanation of function for each port.
Parallel Port
Parallel ports can be used to connect a host of popular computer peripherals
like: Printers, Scanners, CD burners, External hard drives, Network adapters
and Tape backup drives. Parallel ports were originally developed by IBM as a
way to connect a printer to PC. Parallel ports are also known as LPT ports.
When a PC sends data to a printer or any other device using a parallel port, it
sends 8 bits of data (1 byte) at a time. These 8 bits are transmitted parallel to
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each other all at once. The standard parallel port is capable of sending 50 to
100 kilobytes of data per second.
The original specification for parallel ports was unidirectional, meaning that
data only traveled in one direction for each pin. With the introduction of the
PS/2 in 1987, IBM offered a new bi-directional parallel port design. This mode
is commonly known as Standard Parallel Port (SPP) and has completely
replaced the original design. Bi-directional communication allows each device
to receive data as well as transmit it.
Figure 1.13 Computer ports
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Serial ports, also called communication (COM) ports, support sequential data
transmission and are bi-directional. As explained above, bi-directional
communication allows each device to receive data as well as transmit it. The
name "serial" comes from the fact that a serial port "serializes" data. That is, it
takes a byte of data and transmits the 8 bits in the byte one at a time serially
one after the other. The main advantage is that a serial port needs only one wire
to transmit the 8 bits (while a parallel port needs 8 because all 8 bits are sent in
one go). The disadvantage is that it takes 8 times longer to transmit the data
than it would if there were 8 wires. Serial ports lower cable costs and make
cables smaller. A serial port is commonly used to connect external modems,
scanners or the older computer mouse to the computer.
It comes in two versions, 9-pin and 25-pin. 25-pin COM connector is the older
version while the 9-pin connector is the current standard. Data travels over a
serial port at 115 Kb per second.
Most computers have at most two serial ports, and they are very slow in most
cases.
Devices that needed faster connections came with their own cards, which had
to fit in a card slot inside the computer's case. Unfortunately, the number of
card slots is limited and a Ph.D. was needed to install the software for some of
the cards.
USB (Universal Serial Bus) Port
USB, introduced in 1997 is a plug and play peripheral connection, which was
invented to solve all these headaches. It is used to connect various devices, for
example, digital joystick, a scanner, digital speakers, digital cameras, or a PC
39

telephone etc. to the computer. USB is generally a two-and-a half-inch long
port on the back of computers or built into a hatch on the front of a computer.
The Universal Serial Bus provides a single, standardized, easy-to-use way to
connect up to 127 devices to a computer. Just about every peripheral made now
comes in a USB version. A sample list of USB devices that you can buy today
includes: Printer, Scanner, Mic, Joystick, Flight yoke, Digital camera,
Webcam, Scientific data acquisition device, Modem, Speaker, Telephone,
Video phone, Storage device such as Zip drive, Network connection.
Connecting a USB device to a computer is as simple as finding the USB
connector on the back of the machine and plugging the USB connector into it.
If it is a new device, the operating system auto-detects it and asks for the driver
disk. If the device has already been installed, the computer activates it and
starts talking to it. USB devices can be connected and disconnected at any time.
Many USB devices come with their own built-in cable, and the cable has an
"A" connection on it. If not, then the device has a socket on it that accepts a
USB "B" connector.
The USB standard uses "A" and "B" connectors to avoid confusion: "A"
connectors connect towards the computer while the "B" connectors connect to
individual devices. By using different connectors it is impossible to ever get
confused. Connect any USB cable's "B" connector into a device and it is sure to
work.
The Universal Serial Bus is the hottest product in the computer market because
of the following features:
•The computer acts as the host.
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•Up to 127 devices can connect to the host, either directly or by way of
USB hubs.
•Individual USB cables can run as long as 5 meters; with hubs, devices
can be up to 30 meters (six cables' worth) away from the host.
•With USB 2, the bus has a maximum data rate of 480 megabits per
second.
•A USB cable has two wires for power (+5 volts and ground) and a
twisted pair of wires to carry the data.
PS/2 Port
IBM developed the PS/2 port. It is also called a mouse port. It is used to
connect a computer mouse or keyboard. A PS/2 connector is a round connector
with 6 pins. Nowadays few computers have two PS/2 ports, one for keyboard
and one for mouse. A colour code is used to distinguish between the two ports
the keyboard port is green and the mouse has a purple port. In earlier
computers the keyboard was connected using a 5-pin DIN connector with a
small notch on one side. The purpose of keeping the notch was to avoid a
wrong connection. With the advent of the PS/2, this socket has become
obsolete.
1.7.2 Monitor Socket
This connector is used to attach a computer display monitor to a computer's
video card. The connector has 15 holes.
Audio/Speaker and Microphone Socket
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At the back of the computer system we can find three small sockets of blue,
green and pink colors used to connect speakers, audio input devices and
microphones to the PC respectively. The connectors for microphone and
speakers are color coded to help in troubleshooting.
1.8 Review questions
1.Differentiate between the following:
a) Input and output units of computer.
b) RAM and ROM.
c) Secondary memory and primary memory.
d) Tension arm tape drive and vacuum column tap drive.
e) PROM and EPROM.
2.Thousands of different computers have been designed and built during the
evolution of the modern digital computer. Each of these computers has
been classified into generations. Mention and explain five generation of
computers. For each generation mentioned point out the hardware
technology used, their characteristics, and the features that differentiate
each one from the other
3. What is computer? For what purpose it is used? Outline four (4)
characteristics of a computer.
4. Name any three places, where computers can be used?
5.Draw a block diagram of computer, label its component and give the
organizational relationships (data flow) that exist among them.
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6.Describe the role of keyboard and mouse in computer? What are the
fundamental similarity and differences between them?
7. List the input and output devices.
8.What is the role of memory in computer? Name any two medium, which
serve the purpose of permanent memory.
9.What do you understand by logical operations? Which part of computer
performs arithmetic and logical operations?
10. Describe the term hardware and software. What is program in relation to
computers?
11. Describe the role of control unit in computer.
CHAPTER TWO: COMPUTER SOFTWARE
2.1 Introduction
A computer system is basically combination of hardware and software. For its
functioning it requires different types of hardware devices, electronic
components and various types of software. The term software refers to the
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instructions that enable the computer to perform its tasks. There are basically
two types of software: the system software and the application software.
2.2 Applications Software
Application software, programs used by a computer user to perform a certain
task like word processing, spreadsheets, etc to be followed by computer. There
of two types’ specific purpose and General purpose application software.
2.2.1 Specific purpose
These packages are written to carry out a prescribed set of tasks and the user
has very little control over the process. E.g. the payroll package, the user is
prompted to enter the employee number, payroll number, number of hours etc.
the program then calculates the deductions such as tax and determine the final
wage of the employee; the program the print the employee’s pays lip. The role
of the user is restricted to feeding the machine with the appropriate answers. A
menu may allow different reports to be generated but there is no opportunity to
deviate from pre-programmed activities. Other examples includes Accounting
packages, Stock control software, Human resource packages etc.
The Advantages of specific purpose application software includes:
• It involves little training, since the program produce a series of simple
tasks that is easy to carry out.
• Comprehensive error checking. All likely errors that can be made by
users are predicted in advance and the program is written to prevent the
user from entering erroneous information.
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But the big disadvantage of this is that programs which are specific to the
company’s needs are not available off the shelf and have to be specially written
by a software house, which is a very expensive business.
2.2.2 General purpose
With general-purpose software, the general routines are included in the
packages but the user has great deal of influence over how they are used. With
this package the user controls the software and not the other way round.
Consider a word processing package. The program will have fixed facilities to
enter data, modify it, move it around, check it for correct spelling or grammar,
etc. these facilities will be available to anyone who uses the package. The
different lies on how each user takes advantages of the facilities. One user’s
output may be a best novel or a love poem.
The normal commercial sector of industry also has great use for general-
purpose packages such as spreadsheets (e.g. Lotus, excel, Quattro) and
databases (e.g. dBase, FileMaker, Access). These packages provide basic
facilities and these are used to put together a system that can be used by
ordinary operators. So, one company might tailor a spreadsheet to provide a
budget program while another company might produce a sales forecasting
program. The most popular general purpose application programs are described
below:
• Word processing software, such as Microsoft Word, is used for
producing reports, letters, papers, and manuscripts.
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• Desktop publishing software, such as Adobe In-Design, helps you use
graphic design techniques to enhance the format and appearance of
documents such as newsletters, brochures, newspapers, and magazines.
• Web authoring software, such as Microsoft FrontPage or Macromedia
Dreamweaver, helps you design and develop customized Web pages
• Spreadsheet software, such as Microsoft Excel, helps you create
worksheets to perform calculations, create “what-if” analyses, and graph
data.
• Database software, such as Microsoft Access, helps you keep track of
related data and records. Other functions include finding, organizing,
updating, and reporting information stored in more than one file.
• Presentation software, such as Microsoft PowerPoint, helps you to
combine text, graphics, animation, and sound into a series of electronic
slides.
• E-mail software, such as Microsoft Outlook, helps you to send and
receive e-mail messages over the Internet.
From chapter three the three general purposes application software will be
discussed, these are Word processing software (MS Word), Spreadsheet
software (MS Excel) and Presentation software (MS PowerPoint)
2.3 System software
These are the software which affect directly the operations the computer. They
are designed to facilitate the efficient use of the computer’s resources and aid
in development and execution of the application programs.
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For example, one system program allocates storage for data being entered into
the system; another system program instructs output to be sent to the
appropriate device such as a line printer.
A system programmer maintains the systems programs in good running order
and tailors them, when necessary, to meet the organization requirement. Since
system programmers serve as a bridge between the computer and the
application programmers, they must have a technical background needed to
understand the complex internal operations of the computer.
System software appears on all computers in one form or another, the most
common control software includes the Computer’s operating system, device
drivers, and so forth. In the next section we will discuss the Operating system
in detail.
2.4 Operating System
An operating system controls the resources and components of the computer. It
consists of many specialized programs, each of which performs a special task.
One task controlled by the operating system is the allocation of the computer’s
RAM to application programs. The operating system is also responsible for the
synchronization of hardware components such as the monitor, printer, and disk
drives.
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2.4.1 What Is Operating System
Operating System is essential software that is required for a computer to
become operational. It provides functionality to computer hardware so that
electro-mechanical components of it perform read, write and processing
functions as human beings do.
Without operating system, computer hardware is useless. In the absence of
operating system, neither input devices will be able to provide data to the
computer nor memory will be able to store anything in it nor processor will be
able to process the data nor will output devices be able to show the result.
Managing computer's resources and making them work in coordination with
each other is the responsibility of operating system.
Any instruction given by the user to the computer to perform a function is
actually carried out by operating system. It is the operating system, which on
receiving instructions from the user invokes all internal units to perform their
duties and workout the result. Details of operating system are described below.
Operating system is essential software, purpose of which is to activate the
computer and:
1. Perform internal management functions
2. Provide services.
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Internal management functions are the functions that have to be essentially
performed to make the computer work. For example, managing the processor,
memory, devices, input / output functions, data etc
Services are bunch of commands and utilities that operating system provides to
its users to have better control over computer. Block diagram, showing the
basic structure of operating system is shown in figure 2.1. It also depicts its
purpose.
Figure 2.1 Basic OS structure
2.4.2 Functions of an Operating System (OS)
i. It eliminates the human intervention with the computer. Human being does
not need to understand the computer language, a user use its own language
but the OS covert it into computer language.
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ii. It works as a resource manager, it allow several program to share computer
resources. The OS allocates the resource to the programs requesting them
and resolves conflicts that occur when, for example, two or three request
the use of the same tape driver or primary storage location. Not only that
but it perform an accounting function; i.e. it keeps track of all resource
usage so that user fee can be determined and the efficiency of CPU
utilization evaluated.
iii. OS schedule jobs on priority basis although it may seem logical to run
program in the order in they are submitted, this is not the most practical
approach. For instance, assume five programs are submitted for processing
within short period of time. Suppose one program requires one minutes of
the CPU time and the other four require one hour each. It may be
reasonable to process the short program first. Or suppose one program will
provide a vital report and the output of the other is less important. The most
important program should probably be processed first.
2.4.3 Examples of Operating System
To activate the computer and to perform different types of activities on
computer, many operating systems are available these days. MS-DOS,
Windows, Linux, UNIX etc. are few popular operating systems of modern
time. Each operating system has its own advantages and disadvantages. As per
its design and features each operating system offers its own style of working
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and commands. However in this course we will concentrate mainly in windows
operating system with highlight on the MS DOS.
MS-DOS
MS-DOS is one of the most popular, powerful and useful operating system. It
was designed and developed in the initial days of Personal Computers (PC) by
Microsoft Corporation of USA. Due to its versatility and ease of operations, it
became quite popular, within short span of time.
MS-DOS is Character User Interface (CUI) based operating system. To execute
any command in MS-DOS, you need to know the command and its format.
Any mistake in its spelling or format leads to error. MS-DOS not only activates
computer resources and controls them but it also provides many commands for
performing day-to-day tasks.
Windows OS
Windows is the most popular operating system of modern times. It has been
designed and developed by Microsoft Corporation of USA. Windows not only
activates computer and makes its devices functional, it also provides
applications for performing wide variety of tasks on computer. For example, its
Notepad program enables you to write letters and notes. Using its Paint
program you can draw pictures on computer and color them too. Likewise there
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are many more programs in Windows; in our case we will focus on windows
OS. Generally windows OS have the following features:
GUI Based Operating System
GUI is acronym for Graphical User Interface. Windows is Graphical User
Interface based operating system. It provides very simple, yet powerful and
interesting mechanism for interacting with computer.
In GUI interaction, you don’t interact with computer by typing commands, as
you do in MS-DOS. Instead of this you make use of graphical items like icons,
menus, buttons, dialog boxes etc. As and when required, these items appear on
computer screen and you click, double click or right click the mouse on them to
carryout required tasks. Thus in GUI mode of interaction, you need not
remember the commands and their formats to perform the task, rather you
should know the method of clicking, right clicking, dragging and dropping the
items.
Multitasking Operating System
Windows is multitasking operating system. Thus in Windows, you can perform
multiple tasks simultaneously. For example, while typing the letter through
keyboard, you can view a movie on VDU and print the report on printer too.
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Drag and Drop
Drag and Drop is a powerful feature of Windows operating system. Using this
feature, you can drag objects like files, folders etc. from their original location
and drop them at some other place, so that they could either be copied or
moved there. For example, dragging the file A from folder F1 and dropping it
on folder F2 will move the file A from F1 to F2.
CUT, COPY and PASTE
Cut, Copy and Paste are powerful features of Windows operating system.
Using these features, selected item like text, graphics, icons etc. can either be
copied from their original place to a temporary memory location called
Clipboard or from Clipboard to the desired location. Thus you can either move
these items from one place to other or make duplicate copies of them. For
example, when you select an item and perform CUT operation on it, it
physically moves from its original place to the Clipboard. When you move to
some other location and perform PASTE operation there, the item from
Clipboard gets copied to the current location. Thus at the end of CUT-PASTE
operation, selected item changes its place. Similarly when you perform COPY
operation on a selected item, it get copied into Clipboard (doesn’t get removed
from its original place, as it happens in the case of CUT operation). After this,
when you change your current location and perform PASTE operation there,
contents of Clipboard get copied to the new location. Thus a duplicate copy of
the selected item gets made.
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Object Embedding
This is one of the most powerful features of Windows operating system. It
enables two or more programs to exchange objects like text, graphics etc.
among them. For example, a drawing made in Paint program could be brought
into the document, created through WordPad program so that figure could be
embedded in the text.
Object Linking
Object Linking is yet another powerful feature of Windows operating system.
Using this feature, one object can be linked to the other object. Thus whenever
linked object is modified or changed, modifications/changes get visible in other
object also. For example, you may type the description of Personal Computer
in WordPad program and draw its figure in Paint program. Using Object
Linking feature you may link the computer figure to computer description so
that it appears in the document. Now whenever you will make
modifications/changes in computer figure they will automatically get reflected
in the description. You may note that overall effect of Object Embedding and
Object Linking is same but automatic reflection of changes/modifications does
not take place in case of Object Embedding.
Plug and Play
It is an important feature of Windows operating system. It makes the operating
system, slightly intelligent. Whenever a new device is attached to the computer,
operating system automatically senses its attachment and loads its device
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driver. Thus due to plug and play feature, new devices become automatically
operational in Windows operating system.
Command Prompt
Using this feature, Windows provides MS-DOS working environment, within
Windows environment. Thus all MS-DOS commands could be executed from
Windows.
2.4.4 Booting Computer with Windows
To boot the computer with Windows operating system, first switch the monitor
on and then switch on the CPU, using ON/OFF switch present in its chassis.
When you do so, computer will check all its peripherals, if they are functioning
properly or not. If any unit is found faulty, an error message appears on the
screen and booting process stops. On the other hand, if all the units are found
OK, booting process continues. Computer reads the operating system from the
disk loads it into memory and displays a window, as shown in figure 2.2.
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Figure 2.2 Loading the windows OS
2.4.4 Introduction to Windows Desktop
After booting the system with Windows, the first screen that appears on the
monitor is called Desktop. Desktop is illustrated in figure 4.2. A brief
introduction of each component of Windows desktop is given below.
Desktop Icons
Icons are graphical pictures. They represent objects like programs, files, folders
etc. Initially few icons appear on desktop. Later, if the need be, more icons are
placed on the desktop. To activate any icon, you need to double click the
mouse on it.
Start Button
Start button is the starting point of Windows menu system. When you click the
mouse on "Start" button, Start menu, as shown in figure 2.3 appears on the
screen.
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Figure 2.3 Start button Popup menu
Refer Start menu, shown in figure 2.3 and note the following points:
1. Some of the options in Start menu have an arrow marked in front of them.
This arrow indicates that when you click the mouse on the option, a
submenu will appear on the screen.
2. Some of the options have few dots (…) marked in front of them. These
dots indicate that when you click the mouse on the option, a dialog box
will appear on the screen.
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3. Those options that neither have arrow nor dots marked in front of them
get directly executed when you click the mouse on them.
Quick Launch Toolbar
As illustrated in figure 4.2, Quick Launch toolbar comprises of many buttons.
Each button represents a program. When you click the mouse on any button,
corresponding program gets executed.
Task Manager
Initially, Task Manager appears as blank area but when you execute any
program, a button for that program gets created in this area. This button
identifies the program and provides means for performing different operations
on the running program. For example, using the button you could terminate the
program.
System Tray
Initially system tray displays few icons and system time in it. Each icon of the
system tray represents a program, which is invisibly running in the background.
To operate upon a background program, you can double click the mouse on its
icon. For example, to set the system date and time, you can double click the
mouse on system time icon.
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2.4.5 Windows Applications
Windows is a powerful operating system. It not only makes the computer
functional, it also provides many useful programs using, which you can
perform, different types of operations. Following are commonly used programs
of Windows:
Notepad- This program is used for creating small text files.
WordPad- This program is used for creating large text files. It also provides
many formatting options, using which the document could be formatted and
made attractive.
Paint: It is basically a drawing and coloring program. Using this program, you
can create shapes and drawings and color them with attractive colors.
Calculator: Using this program, you can use your computer as calculator and
perform arithmetic and scientific calculations.
Media Player: Using this program, you can play audio and video files on your
computer.
Movie Maker: Using this program, you can put graphical pictures in sequence
and prepare multimedia presentations.
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Windows Explorer: Windows Explorer is a program, using which file and
folder maintenance activities are performed on computer. Creating new folders,
deleting old folders, moving or copying files from one folder to another are the
activities, which are easily performed with the help of Windows Explorer.
Internet Explorer: Internet Explorer is basically a browser, using which
activities like net surfing, net search, e-mail etc. are performed.
2.4.6 GUI Components of Windows
Windows is Graphical User Interface (GUI) based operating system. While
working with this operating system, you interact with the computer through
many GUI components. A brief description of commonly used GUI
components of Windows is given below.
Program Icons
All those icons that represent program are called Program icons. Some of the
program icons are illustrated in figure 2.4. To run the program, you need to
double click the mouse on its program icon. For example, to execute Date/Time
program, you will have to double click the mouse on its icon.
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Figure 2.4 program icon
Objects Icons
All those icons that represent objects like devices, files, folders etc. are called
object icons.
Some of the object icons are illustrated below.
To select an option from the bar menu, you need to either click the mouse on
the option or press underlined key along with ALT key. For example, to select
Edit option from the bar menu, you can either click the mouse on Edit option or
press ALT and E keys together. This combination of ALT and underlined key
is called hot key.
Pull Down Menu
Pull down menus appear as submenu, when you select an option from some
other menu. For example, when you select any option (say Edit) from the bar
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menu, a pull down menu appears on the monitor screen. To select an option
from the pull down menu, you need to click the mouse on it.
Popup Menu
These menus appear as independent menus, when you click the left button of
your mouse on some object. They automatically disappear when you click the
mouse at some other place. For example, when you click the mouse on "Start"
button, Start menu pops up as an independent menu. These menus do not
appear everywhere but remain available at some special location. A popup
menu is illustrated in figure 2.3.
Shortcut Menu
Shortcut menus appear when you right click the mouse. For example, when
right click the mouse on desktop; a shortcut menu appears on the monitor
screen. To select an option from the shortcut menu, you need to click the
mouse on the option. When you select the option, corresponding activity takes
place and popup menu disappears from the screen.
Toolbars
A row of small buttons, with icons in them forms a toolbar. Each button
performs a specific task when you click the mouse on it. To find out, what a
button of toolbar does, rest the mouse pointer on the button for a while. Don't
click on it, a label called tool tip will appear near the button. Generally labels
are such that they give idea of button's function.
Dialog Box
A dialog box is special type of window that allows you to enter specifications
for performing a task, as per your choice. For example, when you open a file, a
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dialog box, appears on the screen. Using this dialog box, you can specify drive,
folder, file name etc. of the file, which you wish to open.
Menu Bar
Bar menu appears in the form of a horizontal strip, with options written inside.
A typical bar menu, is illustrated in figure 2.5. To select an option from the bar
menu, you need to either click the mouse on the option or press underlined key
along with ALT key. For example, to select Edit option from the bar menu, you
can either click the mouse on Edit option or press ALT and E keys together.
This combination of ALT and underlined key is called hot key.
CHAPTER THREE: WORD PROCESSING SOFTWARE
3.1 Word processing concepts
Word processors are application programs used for creating, editing, printing
and saving documents. By using a word processor it is possible to prepare
reports, announcements, journals, books, etc. In this unit you will learn about
Microsoft Word 2007, the most popular word processor of nowadays computer
world. This product has so many features that it is not possible to learn all in
one experiment, nevertheless after completing this chapter you will not only be
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able to do a lot of these things, but also learn how to learn the other features by
yourself, using Help Menu.
A key advantage of word processing software is that users easily can make
changes in documents.
3.2 Common features of word processor
Insert text and delete text
Allows you to insert text anywhere in the document and erase characters,
words, lines, or pages as easily as you can cross them out on paper
respectively. The insertion of text is done at an insertion point. See figure
below
Word-wrap
This feature enables Automatic arrangement of text in lines of specified length
without the necessity of touching the return key. The word processor
automatically moves to the next line when you have filled one line with text,
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and it will readjust text if you change the margins. The following diagram
shows an example of word wrap in word 2007. When the sentences reaches the
end it automatically start another line.
Hyphenation
Option of inserting a hyphen to break a word that ends a line: the hyphen does
not print if later editing moves the word to the middle of a line. The following
figure shows the hyphenation at word necessity that is ne-cessity
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Alignment:
Positioning text or numbers to specified margin and tab settings. there are four
alignment options- left, right, center and justification (or full justification). In
justification the text is aligned in both the left and right margins. See the figure
below
Decimal Alignment:
Positioning columns of numbers with the decimal points vertically aligned.
This figure shows how decimal alignment works. The arrow in diagram shows
the decimal alignment.
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Indents and adjustments
The setting of temporary margins within a document differing from the primary
margins used. Indents determine how close each line of a paragraph comes to
the margin. Adjustments realign of text to new margin and tab settings. Using
this feature it possible to align different paragraph using different margin. The
following shows the four paragraph with different adjustments
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Page size and margins
Allows you to define various page sizes and margins, and the word processor
will automatically readjust the text so that it fits. See the figure for page size
and margin features.
Layout:
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Allows you to specify different margins within a single document and to
specify various methods for indenting paragraphs. The figure below describes
the layout in Microsoft word 2007
Over striking (Over-type)
The substitution of new text for old by typing over the old text. the highlighted
text in following figure shows this feature.
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Search and Replace:
Allows you to direct the word processor to search for a particular word or
phrase. You can also direct the word processor to replace one group of
characters with another everywhere that the first group appears. You go from
edit menu -->Find & Replace.
Copying or Cutting and paste
This allows the duplication or moving of blocks of text within a document. The
Clipboard group in ms word 2007 embeds these features. See figure below.
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Template (Boilerplate)
This are predesigned documents that have preset margin, fonts, paragraph
formats, heading etc from which standard documents can be built. When you
define your template make sure you save it as a template and not a normal
document. The figure below shows how you can save in template in MS Word
2007. The highlighted option saves a document as template
Sections
Word processor allows you to divide a document into sections and apply a
different format to each section. The following figure shows the document with
two sections
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Column
The pages can be divided into different columns. This can be used when
creating a newsletter.
Headers, Footers and Page Numbering
Allows you to specify customized headers and footers that the
word processor will put at the top and bottom of every page.
Also it provides automatic sequential numbering of pages. The
figure show an example of footer and page number in Ms Word
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Form Letter Merging
Automatic combining of a form letter with a mailing list to generate multiple
copies of the letter with the different addresses and other variable information
filled in. This is particularly useful for generating many files that have the same
format but different data. Generating mailing labels is the classic example of
using merges. See the figure below.
File management
Many word processors contain file management capabilities that allow you to
create, delete, move, and search for files.
Font specifications
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Allows you to change fonts within a document For example, you can specify
bold, italics, and underlining. Most word processors also let you change the
font size and even their typeface. In Ms Word there is Font group for this task.
See the figure below.
Footnotes/endnotes and cross-references
Automates the sequential numbering and placement of footnotes/endnotes and
enables you to easily cross-reference other sections of the document. See the
figures below
Graphics
This allows you to embed illustrations and graphs into a document. Some word
processors let you create the illustrations within the word processor; others let
you insert an illustration produced by a different program. In MS Word an
illustration group gives this feutres.
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Macros
A macro is a character or word that represents a series of keystrokes. The
keystrokes can represent text or commands. The ability to define macros allows
you to save yourself a lot of time by replacing common combinations of
keystrokes. In Ms Word this feature is not enabled by default. The Screenshot
below shows how macro looks like in MS Word.
Language tools
The word processors contain spellchecker, grammar checkers and thesaurus
utilities to manage the language. Spellchecker is a utility that allows you to
check the spelling of words. It compares words in the text against an on-line
dictionary, flagging items not found in the dictionary by highlight any words
that it does not recognize and offers alternative spellings and a means of
correcting the errors. Grammar Checkers utility works like spellchecker, but
they inspect sentences with grammatical errors. This tool compares yours
sentences against the standard one and notifies you whenever grammatically
sentence is found. Thesaurus is a built-in thesaurus that allows you to search
for synonyms without leaving the word processor.
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Tables of contents and indexes generators
Allows you to automatically create a table of contents and index based on
special codes that you insert in the document
Windows
Allows you to edit two or more documents at the same time. Each document
appears in a separate window. This is particularly valuable when working on a
large project that consists of several different files.
Print:
Allows you to send a document to a printer to get hardcopy.
3.3 Advantages of word processor
a. Corrections can easily be made to your work before a document is printed
or saved. Facilities like spell check further improve the capability to
locate errors and make corrections
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b. Easy formatting of document - for example centering and right
justification. You can also specify fonts, bold, italics etc. You can make
use of the many formatting features available with the software e.g.
borders, text layout
c. You can save your current work, close the document and come back to it
later time
d. Editing your work several times is possible in word processor and you
can save different versions and go back to an earlier one.
e. You can make use of large number of templates available or you could
create your own template and house style
f. You can import data from database or spreadsheet or any other
application and then include it in your document
g. Different type of objects - such as diagrams and pictures can be easily
inserted between text
h. Ability to make templates for your work. If you have lab reports to do
every week, for example, you can create the form that is required and
save it as a template. Then, all you need to do is fill in the blanks.
i. Facilities like mail merge allow a document created once to be used to
create multiple documents with same part of the document changed.
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j. The cut/copy and paste facility makes it easier to copy from one
document to another, or to make a new document by making changes in
copy of another one.
k. The language tools available in word processor software give us
advantages, too. If you misspell a word, possible correct spellings are
offered to you. Some grammatical errors are pointed out to you, although
the Word's grammar checker is not always accurate since it can show
something is incorrect while it is correct. A thesaurus is available in
most word processing programs, too. This offers you synonyms for
words, which can add some variety to your word choices.
3.4 Disadvantage of word processor
a. You need to have access to computer which has word processing software
installed
b. It takes time to learn the program effectively
c. If you want to write something quickly, it takes more time to switch the
computer on, open the word processor and set up the document.
sometimes pen and paper is faster
d. People can become on using word processor and their handwriting skills
can deteriorate
e. People can become reliant on spell checker and not proof reed their work
properly
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3.5 Review Questions
1. What is word processor?
2. What word processors are on our computer?
3. How does spell checker works?
4. What happens when you press Enter key in word processor?
5. What is template? and what is the advantage of using it?
6. What are tab stop?
7. Explain the kind of formatting that you can do on text in word processor
8. What is the difference between spell checker and thesaurus?
9. When do you use an over type mode in word processor?
10. How do I modify text? Bold, Italic, Underline Change the font and size of
text? Change the color of text? Highlight text?
11. How do I make corrections to a mistake which I find later after typing?
12. What is difference between a text file .txt and a formatted document?
13. What is meant by cut and paste?
14. When would you use up and down arrows with a document? When do
you use backspace or delete button ?
15. What’s the difference between using save or save as ?
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16. If you opened a long document, how would you find a certain word in
that document quickly without looking through the entire document
17. As a student how do you use word processors?
18. Give advantages and disadvantages of word processor.
CHAPTER FOUR: ELECTRONIC SPREADSHEET SOFTWARE
4.1 Electronic spreadsheets concepts
Electronic spreadsheet is a software tool for entering, calculating, manipulating
and analyzing set of numbers. These numbers can be changed and the
spreadsheet quickly recalculates the new results. In this chapter you will learn
about Excel, a very popular spreadsheet. This is also application software.
Spread sheets can be used for evaluating results of surveys and elections,
preparing statistical summaries, taking financial decisions, making accounting
calculations, etc…
A spreadsheet allows you to enter rows and columns of information and then to
manipulate the data in a variety of ways. The power of the spreadsheet lies in
the ability to experiment with your data and to see immediately the results of
the changes thus making it easy to perform ‘What if?’ analyses.
Microsoft Excel includes a wide range of statistical functions. However, if you
have a lot of statistical analysis to do, or if the analysis is complex, then you
should consider using a specialist statistical package such as SPSS or SAS.
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Similarly, spreadsheets allow you to sort and select data, but for complex data
manipulation you should consider using a database package such as Access.
Thus, although spreadsheets are powerful and relatively easy to use, do not
assume that a spreadsheet will solve all your problems.
The spreadsheet document is organized in several Worksheets. The collection
of related worksheet you work in is called a workbook. Every worksheet is
composed of a cell. Cell is an intersection of rows and columns and it is
regarded as a smallest building block of worksheet. Columns and rows are
identified by letters (e.g. A, B etc) and numbers (e.g. 1, 2, 3 etc).A cell is
identified by the combination of both letters and numbers e.g. A1, C2 etc. a
group of adjacent cells in a rectangular area is called a range. The cell can hold
many data type but most common are labels, value or numbers, formulas and
dates. The description of each data type is as follows:
1. labels - provide descriptive information about entries in the spreadsheet
2. value or numbers - is an actual number entered into a cell; and
3. Formulas – these are instructions to the spreadsheet program to perform a
calculation. Functions are like preprogrammed (predefined) formula.
4. Dates - shows when was created and can be used in calculation like late loan
repayment
4.2 Common features on most all spreadsheet
Rows and columns
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The spreadsheet is composed by rows and columns. The intersection of row
and column forms the cell where the data can be inserted. The rows are
identified by numbers while the column are identified by letters
Dynamic calculation
A spreadsheet is very fast on a modern computer, so you can set up a powerful
model with thousands of calculations and yet you can expect an answer very
quickly. For example a chart in which whenever the cell contents changes, then
they are reflected to a graph.
Use of formulas
A model needs to be able to do mathematics on the input values and this is just
what formulas can do. Usually the formulas are defined by the individual user
to solve his/her mathematical problem.
Use of functions
This is a real time-saver as spreadsheets have hundreds of functions you can
use for building up the model - for instance there is a function that can do
compound interest calculations. If it did not support functions then you would
have to do all the hard calculations yourself by using formulas. The function
are predefined formulas that come with excel. The following shows how the
functions are included in Ms Excel. The next figure show the use of functions
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Cell Formatting
Cells may be formatted using the format pages, which let you specify the font
style, borders, text and background colors, the size of cells and text alignment
within the cells. Through cell formatting it is also possible to specify height and
width of the cell. The number, alignment and styles can be applicable to cell to
give it an impressive view. The following screen shot shows the groups in Ms
Excel that can be used to format the cell.
Conditional formatting
This feature provides the spreadsheet to apply a certain formatting to particular
data item when certain condition is met. Suppose you have a list of students
who did an exam, through this feature it be easily to locate the student who
failed by making their names font color to be in red. The figure below is dialog
in ms Excel that can be used to make this kind of formatting.
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Multiple Worksheets
Spreadsheet provides support for multiple sheets within a workbook. When you
press the worksheet button, worksheets are presented in a horizontally
scrollable page, allowing you to quickly flick between all the worksheets in the
workbook. A worksheet may be selected simply by tapping on it. You can
create new worksheets and delete or rename existing worksheets. You can also
create cross-sheet formulas and copy and paste between sheets.
Searching and Sorting
Spreadsheet provides the ability to search the worksheet for any phrase,
number or other text, letting you easily scroll between search results. It is also
possible to sort a range of cells by any row or column. The editing group in MS
Excel provides these features. See the figure below.
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Graphs and Charts
Graphs and charts let you present the data in a visual or pictorial form. Humans
find it easier to spot trends and analyses data in a graph rather than in a table of
numbers.
Data Analysis
Spreadsheet software gives you the ability to analyze your data in ways other
than simply looking at grids and lines. Most spreadsheet software can
automatically create graphs and charts from your data, giving you different
ways of comparing and analyzing information. These visual representations can
also be printed and emailed, or exported into slide shows for presentations.
Examples of analysis are what-if analysis and goal-seeking analysis. Besides
the graphs and charts, spreadsheet provides features for filtering and sorting.
Also using What-if analysis feature it possible to have advanced way of
analyzing your data. The figure below shows some the analysis tools that are
present in MS excel 2007
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Protect and password cells
To give the security to your content, spreadsheets provides the password
facility to protect an individual cell or the whole document.
Pivot tables and Pivot Charts
The Pivot Tables tool is one of the most powerful yet intimidating features in
Excel. Pivot tables allow you to quickly summarize and analyze large amounts
of data in lists and tables--independent of the original data layout in your
spreadsheet--by dragging and dropping columns to different rows, columns, or
summary positions. Use a PivotChart report to visualize that summary data in
a PivotTable report, and to easily see comparisons, patterns, and trends. Both a
PivotTable report and a PivotChart report enable you to make informed
decisions about critical data in your enterprise.
Look Up tables
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All spreadsheets support lookup functions, tools that return a value from a table
by looking up another value in the table.
4.3 Ms Excel Formulas and Functions
One of Excel's most useful features is that it allows users to create custom
formulas to perform calculations on their data. Excel also contains built-in
formulas called functions that make it easy to perform common calculations on
data. Here you will find step by step tutorials, tips and shortcuts on how to use
formulas and the common and less common functions available in Excel.
Formula Basics
Formulas in Microsoft Excel begin with an equal sign. The equal sign tells
Excel that the succeeding characters constitute a formula. If you don't enter the
equal sign, Excel will treat your entry as text and the calculation will fail.
To show how formulas work, we'll begin with a simple exercise by selecting
blank cell A1. Then type =5+5, and press Enter. Excel performs the calculation
and produces a result of 10 in cell A1.
Notice the formula bar shows the formula you just
typed. What appears in the cell is the result; what
appears in the formula bar is the underlying value,
which is a formula in this case.
Order of Operation
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When performing calculations in a formula, Excel follows certain rules of
precedence: Excel calculates expressions within parentheses first. Excel
calculates multiplication and division before addition and subtraction. Excel
calculates consecutive operators with the same level of precedence from left to
right.
For example, the formula = 10+10*2 gives a result of 30 as Excel multiplies 10
by 2 and then adds 10. However, the formula =(10+10)*2 produces a result of
40. This is because Excel calculates the expression (10+10) within the
parentheses first. It then multiplies by 2.
If you want to overrule the precedence order in which Excel calculates, use
parentheses. Parentheses also make your formulas easier to read.
4.3 1 Ranges and Individual Cells
As you start to write excel formulas, you
may realize you want to use a range of cells
or nonadjacent cells in your formula. A range of cells will include the value of
every cell within the range specified (for example, the range A1:A4 includes
the cells A1, A2, A3 & A4). Ranges of cells are identified with a colon.
Nonadjacent cells can be listed in the formula by separating them with a
comma rather than a colon. For example, =SUM(A2,A4) will add cells A2 and
A4, but not A3.
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Copy a Formula
There two ways of copying the formula
1. Using the Fill Handle
2. Using Traditional Copy & Paste
Referencing Cells in Formulas
You can include or reference other cells in a formula. When you do, the result
of the formula depends on the values in the referenced cells and changes
automatically when the values in the referenced cells change. This is extremely
powerful in what-if scenarios.
To see how this works, enter 10 in cell A1. Now select cell A2 and type
=A1*2, and press ENTER. The value in cell A2 is 20. If you change the value
in cell A1 from 10 to any value, the value in cell A2 will also change. Cell
references are especially helpful when you create complex formulas, or
conduct what-if analysis.
Relative Cell References
By default Excel uses Relative Referencing. In relative reference, you actually
refer to cell that is above or below or left or right to a number of rows or
columns. For example, if you refer to cell D2 from F2, you are actually
referring to a column that is two columns to the left of cell D2 and in the same
row (the second ‘2’row). When a formula that possesses a relative reference is
copied from one cell to another cell, the value in the copied cell also changes.
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i.e., if you copy a formula =C2+D2 from E2 to the cell F2, the formula in F2
adjusts in such a way that when the cell F2 is dragged downwards by one row,
the formula automatically changes to C3+D3 and places the resulting value of
C3+D3 in cell F3.
Absolute Cell References
In case, if you wish to maintain the original references as they were, then you
should make use of the absolute references. If you want to make the above
example retain the original reference when it is copied, then you should
precede the columns A2 and B2 and the row number by a Dollar ($) symbol.
i.e., you should use the formula as =$C$2+$B$2 so that when you copy the
formula the original reference is retained.
To make the cell appear in absolute format ($) click on the cell you would like
to edit and press [F4] and press enter. You will observe the cell A1 turn into
=$A$1.
For example, if you copy or fill an absolute reference in cell B2 to cell B3, it
stays the same in both cells =$A$1.
Mixed Cell References
In some situations, you may need to make the cell reference as ‘Mixed’
reference, so that you can lock either a column or a row by preceding it with a
Dollar ($) symbol. For example, if you use a formula as =$D4+E4, then you
are making the value that is present in cell D4 as absolute and the value in cell
E4 as Relative.
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Understand Error Values
Common errors in MS excel:-
• ##### The column is not wide enough to display the content. Increase
column width, shrink contents to fit the column, or apply a different
number format.
• #REF! A cell reference is not valid. Cells may have been deleted or
pasted over.
• #NAME? You may have misspelled a function name
4.3.2 Commonly Used Functions & Formulas
Below is a list and description of commonly used formulas within Excel.
AVERAGE Function
The AVERAGE function, one of Excel's statistical functions, is used to find the
average or arithmetic mean of a given list of arguments.
The syntax for the AVERAGE function is: = AVERAGE ( argument1,
argument2, ... argument255 ) Argument1, argument 2, … argument 255 can be
numbers, named ranges, arrays, or cell references.
Tip: Up to 255 arguments can be entered.
MAX Function
The MAX function, one of Excel's statistical functions, is used to find the
largest or maximum number in a given list of values or arguments.
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The syntax for the MAX function is: =MAX( argument1, argument2, ...
argument30 )
Argument1 ... argument 30: The arguments can be numbers, named ranges,
arrays, or cell references. Up to 30 arguments can be entered.
MIN Function
The MIN function, one of Excel's statistical functions, is used to find the
smallest or minimum value in a list of numbers or arguments.
The syntax for the MIN function is: =MIN ( argument1, argument2, …
argument30 )
Argument1 ... argument 30: Arguments can be numbers, named ranges, arrays,
or cell references. Up to 30 arguments can be entered.
PRODUCT Function
The PRODUCT function provides a quick way to multiple numbers in a Excel.
The advantage of using this function becomes apparent if you have several
numbers to multiply together. It is easier then building a long formula.
The syntax for the PRODUCT function is: =PRODUCT( Number1, Number2,
… Number255 )
TIP: Up to 255 numbers can be entered into the function.
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COUNT Function
Excel's COUNT function is one of a group of Count Functions that can be used
when you need to total the number of cells in a selected range. The COUNT
function's job is to only add up the cells in a selected range that contain
numbers. It ignores empty cells or those contain text. If a number is later added
to an empty cell the function will be automatically updated to include this new
data.
Be aware that dates, times, functions, and formulas are stored as numbers in
Excel. The COUNT function will, therefore, include any cells containing these
types of data in the total.
The syntax for the COUNT function is: =COUNT( Range )
• Range - the group of cells the function is to count.
COUNTA Function
Excel’s COUNTA function is one of a group of “Count Functions” that can be
used when you need to total the number of cells in a selected range. The
COUNTA function's job is to add up the cells in a selected range that contain
numbers,dates, or text labels. It ignores empty cells. If data is later added to an
empty cell the function will be automatically
updated to include the addition.
The syntax for the COUNTA function is: = COUNTA ( Value1, Value2, ...
Value255 )
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Tip: Up to 255 values can be entered into the function.
COUNTBLANK Function
The COUNTBLANK function, one of Excel's COUNT functions, is used to
count up the number of blank cells in a selected range.
The syntax for the COUNTBLANK function is: =COUNTBLANK( Range)
Range - the group of cells the function is to search.
4.3.3 Logical functions
IF Function
The IF function, one of Excel’s logical functions, tests to see if a certain
condition in a spreadsheet is true or false.
The syntax for the IF function is: =IF ( logical_test, value_if_true,
value_if_false )
• logical_test – a value or expression that is tested to see if it is true or
false.
• value_if_true – the value that is displayed if logical_test is true.
• value_if_false – the value that is displayed if logical_test is false.
COUNTIF Function
The COUNTIF function, one of Excel's COUNT functions, is used to count up
the number of cells in a selected range that meet specified criteria.
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The syntax for the COUNTIF function is: =COUNTIF ( Range, Criteria)
• Range - the group of cells the function is to search.
• Criteria - determines whether the cell is to be counted or not. This can be
a number, expression, cell reference, or text string.
SUMIF Function
The SUMIF function is used to add up the values in cells in a selected range
that meet certain criteria.
The syntax for the SUMIF function is: = SUMIF (Range, Criteria, Sum Range)
• Range - the group of cells the function is to search.
• Criteria - determines whether the cell is to be counted or not.
• Sum Range - the data range that is summed if the first range meets the
specified criteria. If this range is omitted, the first range is summed
instead
4.3.4 Lookup & Reference functions
VLOOKUP Function
Excel's VLOOKUP function, which stands for vertical lookup, is used to find
specific information that has been stored in a spreadsheet table. Note: The data
in the table should be sorted in ascending order (alphabetically A to Z).
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The syntax for the VLOOKUP function is: = VLOOKUP ( lookup_value ,
table_array , col_index_num, range_lookup ).
• lookup _value: The value you want to find in the first column of the
table_array.
• table_array: This is the table of data that VLOOKUP searches to find the
information you are after.
The table_array must contain at least two columns of data. The first column
contains the lookup_values.
• col_index_num: The number of the column in the table_array that
contains the data you want returned.
• range_lookup: A logical value (TRUE or FALSE only) that indicates
whether you want VLOOKUP to find an exact or an approximate match
to the lookup_value. Typing False will return exact matches only.
TRANSPOSE Function
The TRANSPOSE function, one of Excel's Lookup & Reference functions, is
used to copy data located in a row into a column or copy data located in a
column into a row.
The syntax for the TRANSPOSE function is: { = TRANSPOSE ( Array )}
• Array - the range of cells to be copied from the horizontal to the vertical
or vertical to the horizontal.
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The curly braces " { } " surrounding the function indicate that it is an array
function.
4.3.5 Date & Time functions
NETWORKDAYS Function
The NETWORKDAYS function, one of Excel's Date and Time functions, can
be used to count the number of working days between two dates - such as the
start and end dates for a project. The function automatically removes weekend
days from the total. Specific holidays can also be omitted.
The syntax for the NETWORKDAYS function is: = NETWORKDAYS
( Start_date , End_date , Holidays )
• Start_date - the start date of the chosen time period.
• End_date - the end date of the chosen time period.
• Holidays - can be used to exclude one or more dates from the total
number of working days (optional).
DAYS 360 Function
The DAYS360 function, one of Excel's Date and Time functions, can be used
in accounting systems to calculate the number of days between two dates based
on a 360-day year (twelve 30-day months).
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The syntax for the DAYS360 function is: = DAYS360 ( Start_date , End_date ,
Method )
Start_date - the start date of the chosen time period.
End_date - the end date of the chosen time period.
Method - A Boolean value (TRUE or FALSE).
• If TRUE -- the function uses the U.S. method of calculating start and end
dates.
• If FALSE -- the function uses the European method of calculating start
and end dates.
WORKDAY Function
The WORKDAY function can be used to calculate the end date or start date of
a project for a given number of business days. The number of business days
cannot include weekend days. Specific holidays can also be omitted.
The syntax for the WORKDAY function is: = WORKDAY ( Start_date , Days ,
Holidays )
• Start_date - the start date of the project or time period in question.
• Days - the number of days work on the project occurred after the
Start_date.
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• Holidays - can be used to exclude one or more dates from the total
number of working days (optional).
NOW Function
The NOW function, one of Excel's date and time functions, is used to add the
current time and date to a spreadsheet.
The syntax for the NOW function is: = NOW ( )
Note: The NOW function takes no arguments.
4.4 Advantages of using Spreadsheets
1 a wide range of built-in functions makes a spreadsheet a very powerful
tool for many types of analysis;
2 it is easy to make repeated calculations on a large number of figures; the
results of any changes to the figures are automatically recalculated and
displayed;
3 spreadsheets include charting facilities which make it very easy to present
results in graphical form;
4 Spreadsheets are used to solve a wide variety of problems such as business
applications, business plans and accounting, scientific calculations and in
various types of data manipulation;
5 Excel can perform both simple and complex calculations, filter data from
a database or spreadsheet list and chart data in a wide range of formats;
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6 The grid encasing the cells in the spreadsheet can either be visible or
hidden in print outs, enabling reports to be formatted from the display of
the spreadsheet.
7 Spreadsheets can also interact with databases to populate reference fields,
automating almost the entire creation phase of the spreadsheet.
8 “What If” Analysis - allow you to change one or more value, view the
results, before the final decision is made on keeping (saving) the
spreadsheet
9 Labour saving from having to calculate large amounts of data by hand
10Templates containing the formulas for regularly used spreadsheets
increase productivity by removing the need for highly educated operators.
4.5 Disadvantages of Spreadsheets
1. Workers no longer need to have specialist skills, and must compete with
cheaper unskilled labor.
2. Individual spreadsheets installed on each of the PCs in an office also
enable individuals to hoard data and make their own forecasts without
cooperating with colleagues.
3. This phenomenon leads to duplication of both data and effort throughout
the organization.
4. The structure of the spreadsheet increases storage requirements over the
needs of raw data.
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5. The results depend on how good the model is and how much data was
used to create it in the first place.
6. The equipment and software are expensive to purchase.
7. Staff need to be trained how to use the software and equipment.
4.6 Review Questions
1. Why do we use a spreadsheet instead of a calculator or paper and pencil?
2. Define the following row, column, cell, range.
3. What is the difference between a spreadsheet and worksheet?
4. Define the difference between the following cell data types: labels,
constants, formulas.
5. What are the uses of spreadsheet?
6. What is the difference between a function and formula?
7. Mention the kind of data analysis that can be achieved in spreadsheet.
8. Why the following statement is true: “It is best to reference as much data
as possible as opposed to typing the data in equation.
9. Name some basic math functions that are building into spreadsheets.
10. How can you copy information from one cell to another?
11. How would you format a number a $?
12. List at least two types of charts that can be created in a spreadsheet
program.
13. Give advantage and disadvantages of spreadsheet
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CHAPTER FIVE: COMPUTER NETWORKING
5.1 Introduction
When two or more objects of same kind join together to work in co-ordination
with each other, they form a network. For example, when many marketing
persons unite together to sell a product, they form a marketing network.
Similarly, when two or more computers connected together with the objective
communicating with each other and sharing their resources, they form a
computer network.
Figure 5.1 computer network
Refer to the figure 5.1 above and note that in this network, four computers are
connected together to form a computer network. In this network, any computer
can communicate with any other computer. For example, computer-1 can send
message to computer-4 and computer-4 can replay back. Similarly, computer -2
and computer-4 can exchange data among them. In computer network,
computers share their resources among them. For example, computer- 3 can
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print its documents on the printer that is attached to computer-4. Similarly
computer- 1, computer -3 and computer-4 can store their data on computer- 2's
disk.
Therefore a computer network can be defined as an interconnected collection
of autonomous computers with the following purposes:
• Resource sharing: programs (O.S., applications), data, equipment
(printers, disks) are available to all users of the network regardless of
location.
• High reliability: By replicating files on different machines and having
spare CPUs, users are more immune from hardware/software failure.
• Less cost: Small machines have about 1/10 the power of a mainframe but
1/1000 the cost. By using such machines with file server machine(s), a
local area network LAN can be cheaply installed. It is easy to increase the
capacity by adding new machines.
• Communications medium: Users have access to email and the Internet
5.2 Types of Computer Networks
Computer networks can be broadly categorized into two categories. One is
called Local Area Network or LAN in short and other is called Wide Area
Network or WAN.
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Local Area Network, as the name suggests, is a network built in a limited area
by using LAN cables, switches and LAN cards. One example is a network of a
university or a business office at one location. The computers on a Local Area
Network are connected to a network switch. You can either make this network
a workgroup (share limited resources) or domain (share all kind of resources
and services). On domain, you have the privilege to grant permissions to users
to share resources or limit them to use certain services. As LAN can only work
within a certain distance, we need WAN to connect institutions and offices at
different locations.
LANs are used in many offices, schools, colleges and hospitals. Because of the
short distances involved they are typically (though not necessarily) faster than
WANs in that it is cheap to use high quality communications media such as
coaxial cable and optical fibre. They can carry data at very high speeds e.g.
from 10 Mbps to 100 Mbps being very common speeds, while speeds of up to
1000 Mbps are possible.
5.2.1 Advantages of LANs
• Hardware such as printers can be shared so individual workstations do not
need their own printer. When they print, the data is stored in a queue on a
server. The data is then passed to the printer.
• All the users work can be stored in a central place (the dedicated file
server) so a user can access their work through any computer on the
network.
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• Software can be shared; software packages are stored on the server and
downloaded to workstations as requested. Note that a license still has to
be bought for each copy of the software needed.
• Data can be shared because database files stored in the server are
available to users around the network; data from CD-ROMs can also be
shared across the network.
• Central back-up can take place automatically at regular intervals. A user
will usually be able to retrieve work that has been deleted by mistake.
• Messages can be sent to people working at other computers on the
network which can save time and paper.
• It is possible to set up a local intranet such as that on the KLB school
network. The web pages of information can be accessed only over the
LAN. An intranet is free because it does not involve phone links.
• There is a control over users’ access rights to programs and data.
5.2.2 Disadvantages of LANs
• Printing can be slow. Where a lot of workstations are served by only one
or two printers, long print queues may develop.
• A virus can spread more easily. If a virus gets into one computer, it is
likely to spread quickly across the network because it will get into the
central backing store.
• As data is shared there is a greater need for security. Users of the network
have to have authentication techniques such as user ids and passwords.
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Unique user ID's control access to the files and settings on the network
while passwords prevent unauthorized users from logging onto the
network. Data may also have to be encrypted so that it is meaningless if
intercepted.
• If the server fails, all the workstations are affected. Work stored on shared
hard disk drives will not be accessible and it will not be possible to use
network printers either.
• The cost of installing the equipment is greater. Cabling can be expensive
to buy and to install.
• Damage to cables can isolate computers. Some sections of the network
can become isolated and will not be able to communicate with the rest of
the network.
• Because networks can be complicated to maintain, a network manager
may be need to be employed to run the system.
A WAN spans a large geographic area, such as a state, province or country.
WANs often connect multiple smaller networks, such as local area networks
(LANs) or metro area networks (MANs) and this is possible with the use of
devices like routers. The world's most popular WAN is the Internet. WANs
generally utilize different and much more expensive networking equipment
than do LANs.
In Wide Area Network, distantly located computers are connected together.
Generally they are located over a distance of more than 1 kilometer. For
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example, when computers of different localities, cities, states or countries are
connected together, they form Wide Area Network.
There are many ways to build a Wide area network. You can either lay down
your own cables between two or more locations or you can use leased lines.
Most companies use leased lines as very limited companies can bear the cost of
thousands dollars for it.
Advantages of WANs:
• These are similar to those of LAN's except the scale of sharing etc.
becomes far greater and can be world-wide.
Disadvantages of WANs:
• Again these are similar to those of LAN's except that issues such as
security become even more important as potential hackers could break
into a computer system from anywhere in the world rather than having to
physically be in a building.
• Encryption of secure data such as financial transactions is necessary
because it is even easier to intercept data.
5.3 Client-Server Model of Computer Systems
Networks often provide services on one or more machines for all users of the
network. The machines providing the service are called servers. The machines
(users) using the service are called clients. Several servers may be used so that
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if one crashes, users can still access their data and the network services. This is
a decentralised computing system whereby users can avail of local processing
on their own machines as well as the shared services of the network.
A good example is a LAN with a file server. The users store files access
software on the file server, but use their own PCs for processing. Dedicated
servers may also be used for email or for printing: mail servers and print
servers.
5.4 Advantages of Computer Network
There are many advantages of computer network. Few of them are described
below:
1. Distantly located information becomes available in no time. For example,
if computer-A at Mwanza is connected with computer-B at Mbeya over
WAN then information among them can be exchanged within few
seconds. This enables efficient working and fast decisions.
2. Costly devices such as magnetic tapes, printers etc. can be shared among
different computers of the network. For example, one printer can be
connected in LAN, so that all the users make use of same printer. This
saves operational cost.
3. Since in a network, many computers remain available for use hence on-
going work continues even if few computers are down. Thus in a
computer network, time and resources are utilized efficiently.
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4. Since distantly located data remains available locally, hence useful
applications can always be developed. One such application is student
admission system
5. Fast communication takes place among different users of the network.
They can exchange words, messages or letters among them. Electronic
mail is the best example of fast communication. Electronic mail neither
gets delayed nor gets lost in transit, as usual mail does.
5.5 The Internet
When many computer networks of the world were connected together, with the
objective of communicating with others and sharing their resources, Internet
was formed. In other words, you can say that Internet is network of computer
networks, which spreads all across the globe. Therefore the Internet can be
defined as a global system of interconnected computer networks that use the
standard Internet protocol suite (often called TCP/IP, although not all
applications use TCP) to serve billions of users worldwide
Initially the size of Internet was small; it was limited to few geographical
locations only. But soon, people become aware of its utility and advantages.
Within short span of time, numerous computers and networks got themselves
connected to Internet. Its size increased multi fold within few years of its birth.
Today Internet comprises of many million computers. There is hardly any
country of the world and important city of the country, where Internet is not
there. A conceptual diagram of Internet is given in figure 11.2.
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Figure 8.2 Conceptual for the internet
Internet is basically a large computer network, which extends all across the
globe. In Internet, millions of computers remain connected together through
well-laid communication system. Recall that telephone communication system
is well-defined, time proven system. Computers of Internet are connected to
each other through this system. Thus like a telephone, any computer of any city
can establish a connection with any other computer of any other city and
exchange data or messages with it.
5.6. Classification of Internet Computers
Computers of Internet can be broadly classified into following two categories:
i. Web Servers
ii. Web Clients
Role and requirements of both types of computers are explained below.
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Web Servers
Those computers of Internet, which provide information or services to other
computers, are called web servers. For example, if a computer in an
organization named Hotmail provides electronic mail services to Internet users
then that computer will be categorized as web server.
Web servers provide services/data to millions of Internet users, so they
generally possess following characteristics:
1. They are fast.
2. They are equipped with large memory and large disk space.
3. They remain connected to Internet all through the day i.e. seven days a
week, 31 days a month and 365 days a year.
4. They make use of fast communication lines.
Web Clients
Those computers of Internet, which take information or services from web
servers, are called web clients. For example, if you make use of Hotmail's web
server to send electronic mail to your friends or relatives then your computer
will be termed as web client. Since web clients interact with web servers on
one-to-one basis and that too when service/information is required hence they
possess following characteristics:
1. They need not be very fast computer.
2. They need not have large memory and disk space as servers have.
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3. They get connected to Internet, when they need information/service from
it. After taking it, they disconnect from Internet.
4. They generally make use of slow connection like telephone lines, to get
connected to Internet.
5.7 Identification of Computers on Internet
Like houses of any city are identified by a unique address, similarly computers
of Internet are identified by a unique address called IP address. IP address
comprises of four numbers separated by dots (.). For example, 150,
075,100.085 is a valid IP address. Each number in IP address can range from 0
to 255. So IP address can range from 0.0.0.0 to 255.255.255.255. Thus if IP
address of a computer is known, it can be accessed over Internet.
5.8 Web Site
Web site is basically, well-identified location on web server, which holds the
information of either an individual or an organization or place etc. Each web
site of Internet is identified by a unique name, called domain name. For
example, suanet.ac.tz, hotmail.com, yahoo.com, indianrail.gov.in, sanchar.net
etc. are valid web sites.
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Domain name comprises of two or more strings of characters separated by dots
(.). First string of characters is called domain name. It identifies the name of the
web site, For example, in suanet.ac.tz, suanet identifies the name of the web
site. Second string of characters identifies the nature of the web site. For
example in hotmail.com, com indicates that it is commercial web site. Standard
strings that are used at second place in the domain name are as follows:
String Type of web site
com Commercial organizations (profit making)
edu Educational institutes
gov Government organization
mil Military
net Network service providers
org Non profit making organizations
Third string in the domain name is always indicative of country.
For example, "in" is used for India. "au" is used for Australia,
"uk" is used for United Kingdom, "fr" is used for "France", “tz”
is used for “Tanzania” etc.
If domain name of a web site is known, it can always be accessed
and its contents can be viewed.
Web Page
Information or services on any web site are arranged in the form
of web pages. A web page may contain elements like text
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graphics, sound, animation video and hyper links in it.
A web site may consist of interlinked multiple web pages. When
you access a web site, its first page gets displayed on your
computer. Since web pages of a web site remain interlinked
through hyperlinks hence you can always access other web
pages, after accessing the first web page.
Hyperlink
When a link between two objects, is maintained in such a way
that when you click the mouse on first object, second object gets
displayed then such a link is called hyperlink.
Hypertext
The text that remains linked to other objects like text, graphics,
audio etc. through hyperlink is called hypertext.
Web Browser
The software, using which you traverse over Internet and access
web sites, is called web browser. Internet Explorer, Netscape,
Mozila, google chrome, etc. are few famous web browsers. Most
of the Internet operations are done, using web browser.
5.6 Searching Contents on Internet
Internet is an ocean of information. Be it any topic, science, culture,
entertainment, tourism, medical or aviation, volumes of information can be
found on Internet. This information remains available on web sites and can be
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availed by visiting the web site Now the questions is, there are millions of web
sites on Internet so how do you come to know, which information is available
on which site and what is its domain name? Well, Internet itself provides
solution for this problem. There are certain web sites, which provide search
facility for searching the content on Internet. For example, yahoo.com is a web
site, which provides search facility. To get the information on any desired
topic, perform following steps:
1. Enter the search term in text box. For example, if you wish to get the
information on "Examination Taking Techniques" enter this term (called,
search term) in the text box and click the mouse on "Search" button.
2. When you do so, a program called Search Engine will search its
information database and find the links to the information. Found links
will get displayed in the form of a list. In technical term, this list is called
"Hit List".
5.7 Introduction to E-Mail
E-mail is a service, using which you can send letters and documents to your
friends and relatives. You can also receive reply from them over Internet within
few seconds. For example, if a letter is sent from Tanzania to America by
normal post, it takes around 15 to 20 days. But if the same letter is sent, using
email, it reaches America within 15 to 20 seconds. On top of this, there remains
no possibility of letter getting lost in the way. E-mail software remains
available in different forms. Most of the commercial web sites provide the use
of this software free to their visitors. For example, yahoo.com, hotmail.com,
rediffmail.com are the names of few web sites, which provide free e-mail
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services to their visitors. If the visitors wish to avail e-mail facility of any web
site then, once forever, they have to open an e-mail account on that web site.
After that they are assigned a unique e-mail address. Using this e-mail address
they can then send and receive letters.
Title Meaning
Sender It signifies the name of the person who has sent the e-mail.
Subject This is the title of the letter, which gives an idea of the contents of
the letter.
Date It specifies the date, on which the e-mail was received.
Size It signifies the size of the mail in Kilobytes.
Other Services of Internet
As mentioned earlier, Internet is an ocean of information and services. Wide
varieties of services remain available on Internet. Whosoever wishes, can avail
these services by visiting the website. Few popular services of Internet are
described below.
1. Internet telephony is a service that enables its users to communicate with
other persons. Using this service an Internet user can ring other person's
normal telephone. If other person picks up his phone, communication
path between the two gets established and they talk in the same way as
two telephone users do. This type of telephony is called Net-To-Phone
telephony.
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2. News group is very popular service of Internet, in which a person has to
become a member of a predefined group. Each group relates to a specific
topic like wind surfing, multimedia, physics, video gaming, vintage cars
etc. Members of the group exchange information, news, problems,
solutions etc. among them.
Due to the categorization of group, likeminded people become the
member of the group. This keeps the discussion inline and helps members
in seeking solutions for their questions and problem from other group
members.
3. These are various web sites on Internet, which provide electronic greeting
cards for all occasions and all reasons. These cards are generally very
colorful, attractive and often animated. People access these web sites and
send card to their friends and relatives.
4. There are various web sites on Internet, which provide facility for reading
newspapers, magazines and articles on Internet.
5. Astrological web sites of Internet provide horoscope, future predictions
and suggestions to the visitors, who visit the web site.
6. There are various web sites on Internet, which provide job opportunities
to the persons seeking job. They also help employers in searching the
right candidate.
7. Music, songs and radio can also be enjoyed over Internet.
8. There are various web sites, which sell different kinds of products. These
web sites can be visited and products can be purchased from there. These
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web sites are often referred to as e-mall. Payment for the purchased items
is made on-line through credit cards.
9. Numerous, free and paid computer games are available on Internet. They
can be downloaded and played.
10. Advance booking in hotels, trains, aero planes etc. can be done
through Internet.
1. What name is given to the activity of visiting web sites?
2. Which software is used for web surfing?
3. Write a valid IP address.
4. Which two words will be essentially there in the domain name of Indian
government web site?
5. Using which service of Internet, people seek advice, opinion, information
and solutions for their problems?
6. Name any two famous services of Internet.
7. What name is given to those computers of Internet, which take
information from other computers?
8. Name a website, which provides search facility.
9. Is Internet an example LAN or WAN?
10. Define the term Internet. Name any three services of Internet.
11. What is IP address? What it is used for? How it is constituted?
12. What is domain name? Write general format of domain name.
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13. How do you search information on a given topic on Internet?
14. What is e-mail? Write at least 2 advantages of e-mail.
15. What is Internet chat? How it is different from news group?
16. What is Internet Telephony? What advantage it has over normal
telephony?
17. What is web browsing? How do you perform it through Internet
Explorer?
18. Explain the term hypertext, by taking a suitable example.
19. Write two advantages of Internet.
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CHAPTER SIX: COMPUTER VIRUSES
6.1 Background
Traditional computer viruses we`re first widely seen in the late 1980s, and they
came about because of several factors. The first factor was the spread of
personal computers (PCs). Prior to the 1980s, home computers were nearly
non-existent or they were toys. Real computers were rare, and they were locked
away for use by "experts." During the 1980s, real computers started to spread
to businesses and homes because of the popularity of the IBM PC (released in
1982) and the Apple Macintosh (released in 1984). By the late 1980s, PCs were
widespread in businesses, homes and college campuses.
The second factor was the use of computer bulletin boards. People could dial
up a bulletin board with a modem and download programs of all types. Games
were extremely popular, and so were simple word processors, spreadsheets, etc.
Bulletin boards led to the precursor of the virus known as the Trojan horse. A
Trojan horse is a program that sounds really cool when you read about it. So
you download it. When you run the program, however, it does something
which is not cool like erasing your disk. So you think you are getting a neat
game but it wipes out your system. Trojan horses only hit a small number of
people because they are discovered quickly. Either the bulletin board owner
would erase the file from the system or people would send out messages to
warn one another.
The third factor that led to the creation of viruses was the floppy disk. In the
1980s, programs were small, and you could fit the operating system, a word
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processor (plus several other programs) and some documents onto a floppy
disk or two. Many computers did not have hard disks, so you would turn on
your machine and it would load the operating system and everything else off of
the floppy disk.
Viruses took advantage of these three facts to create the first self-replicating
programs.
6.2 Origins
People create viruses. A person has to write the code, test it to make sure it
spreads properly and then release the virus. A person also designs the virus's
attack phase, whether it's a silly message or destruction of a hard disk. So why
do people do it?
There are at least three reasons. The first is the same psychology that drives
vandals and arsonists. Why would someone want to bust the window on
someone else's car, or spray-paint signs on buildings or burn down a beautiful
forest? For some people that seems to be a thrill. If that sort of person happens
to know computer programming, then he or she may funnel energy into the
creation of destructive viruses.
The second reason has to do with the adventure of watching things blow up.
Many people have a interest with things like explosions and car wrecks. When
you were growing up, there was probably a kid in your neighborhood who
learned how to make gunpowder and then built bigger and bigger bombs until
he either got bored or did some serious damage to himself. Creating a virus that
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spreads quickly is a little like that -- it creates a bomb inside a computer, and
the more computers that get infected the more "fun" the explosion.
The third reason probably involves bragging rights, or the thrill of doing it. Sort
of like Mount Everest. The mountain is there, so someone is compelled to
climb it. If you are a certain type of programmer and you see a security hole
that could be exploited, you might simply be compelled to exploit the hole
yourself before someone else beats you to it. "Sure, I could TELL someone
about the hole. But wouldn't it be better to SHOW them the hole???" That sort
of logic leads to many viruses.
Of course, most virus creators seem to miss the point that they cause real
damage to real people with their creations. Destroying everything on a person's
hard disk is real damage. Forcing the people inside a large company to waste
thousands of hours cleaning up after a virus is real damage. Even a silly
message is real damage because a person then has to waste time getting rid of
it. For this reason, the legal system is getting much harsher in punishing the
people who create viruses.
6.3 Introduction
Computer viruses tend to grab our attention. On the one hand, viruses show us
how vulnerable we are. A properly engineered virus can have an amazing
effect on the worldwide Internet. On the other hand, they show how
sophisticated and interconnected human beings have become. There are two
key aspects of a virus:
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4. They are self executing. Typically, a virus will attach itself to another
program on your computer, so that it is activated when that program is
used.
5. They are self-replicating. Viruses are designed to spread from machine to
machine and across networks. To achieve this, a virus will usually copy
itself to other programs on a computer, before executing any intended
tasks.
There are a huge number of viruses in existence, carrying varying degrees of
risk. Some are extremely malicious, with the ability to delete or damage files
and programs. Others are less destructive, but prove debilitating by jamming
resources, causing systems to crash with consequent loss. Some of the most
well known viruses are: Bugbear, Klez, Lovebug, Melissa, Bubbleboy, Code
Red, Nimda, ILOVEYOU etc.
For example, experts estimate that the Mydoom worm infected approximately
a quarter-million computers in a single day in January 2004. Back in March
1999, the Melissa virus was so powerful that it forced Microsoft and a number
of other very large companies to completely turn off their e-mail systems until
the virus could be contained. The ILOVEYOU virus in 2000 had a similarly
devastating effect. That is impressive when you consider that the Melissa and
ILOVEYOU viruses are incredibly simple.
6.4 Types of Infection
When you listen to the news, you hear about many different forms of electronic
infection. The most common are:
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20. Viruses - A virus is a small piece of software that piggybacks on
real programs. For example, a virus might attach itself to a program such
as a spreadsheet program. Each time the spreadsheet program runs, the
virus runs, too, and it has the chance to reproduce (by attaching to other
programs) or wreak havoc.
21. E-mail viruses - e-mail virus moves around in e-mail messages,
and usually replicates itself by automatically mailing itself to dozens of
people in the victim's e-mail address book.
22. Worms - A worm is a small piece of software that uses computer
networks and security holes to replicate itself. A copy of the worm scans
the network for another machine that has a specific security hole. It
copies itself to the new machine using the security hole, and then starts
replicating from there, as well.
23. Trojan horses - A Trojan horse is simply a computer program. The
program claims to do one thing (it may claim to be a game) but instead
does damage when you run it (it may erase your hard disk). Trojan
horses have no way to replicate automatically.
6.4.1 Viruses
Computer viruses are called viruses because they share some of the traits of
biological viruses. A computer virus passes from computer to computer like a
biological virus passes from person to person.
There are similarities at a deeper level, as well. A biological virus is not a
living thing. A virus is a fragment of DNA inside a protective jacket. Unlike a
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cell, a virus has no way to do anything or to reproduce by itself -- it is not alive.
Instead, a biological virus must inject its DNA into a cell. The viral DNA then
uses the cell's existing machinery to reproduce itself. In some cases, the cell
fills with new viral particles until it bursts, releasing the virus. In other cases,
the new virus particles bud off the cell one at a time, and the cell remains alive.
A computer virus shares some of these traits. A computer virus must
piggyback on top of some other program or document in order to get executed.
Once it is running, it is then able to infect other programs or documents.
Obviously, the analogy between computer and biological viruses stretches
things a bit, but there are enough similarities that the name sticks.
Different Types of Virus
Although there are a large number of viruses, they fall into three main types:
Macro viruses use features within standard applications, such as
Microsoft Word and Excel, to perform unexpected tasks. For example,
inserting unwanted phrases or figures
File viruses normally affect program files and are usually transferred
by disk, file transfer or e-mail attachments
Boot sector viruses infect parts of your computer that are used when it
starts up, typically the floppy disc and the hard disc. In doing so, the
very act of starting a PC will activate the virus.
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6.4.2 Worm
A worm is a computer program that has the ability to copy itself from machine
to machine. Worms normally move around and infect other machines through
computer networks. Worms are often used to drain computer resources such as
memory and network access, simply by replicating on a large scale. In addition,
worms sometimes delete data and spread rapidly via e-mail. Using a network, a
worm can expand from a single copy incredibly quickly. For example, the
Code Red worm replicated itself over 250,000 times in approximately nine
hours on July 19, 2001.
A worm usually exploits some sort of security hole in a piece of software or the
operating system. For example, the Slammer worm (which caused mayhem in
January 2003) exploited a hole in Microsoft's SQL server.
6.4.3 Trojan Horse
A Trojan horse is a malicious programme, usually disguised as something
useful or desirable. When activated, they can cause loss, damage or even theft
of data.
The critical difference between a Trojan horse and a virus is that a Trojan horse
cannot replicate itself. The only way that a Trojan horse can spread is if you
help it. For example, saving the program from an e-mail attachment, or
downloading it from the Internet.
Just because Trojan horse programs are not self-replicating, it does not mean
that they are less destructive than a virus. Some common features of Trojan
horse programs include:
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f. Making configuration changes
g. Distributing security information
h. Providing unauthorized access paths (known as backdoors and trapdoors)
6.4.4 E-mail Viruses
The latest thing in the world of computer viruses is the e-mail virus, and the
Melissa virus in March 1999 was spectacular. Melissa spread in Microsoft
Word documents sent via e-mail, and it worked like this:
Someone created the virus as a Word document uploaded to an Internet
newsgroup. Anyone who downloaded the document and opened it would
trigger the virus. The virus would then send the document in an e-mail message
to the first 50 people in the person's address book. The e-mail message
contained a friendly note that included the person's name, so the recipient
would open the document thinking it was harmless. The virus would then
create 50 new messages from the recipient's machine. As a result, the Melissa
virus was the fastest-spreading virus ever seen. As mentioned earlier, it forced
a number of large companies to shut down their e-mail systems.
The ILOVEYOU virus, which appeared on May 4, 2000, was even simpler. It
contained a piece of code as an attachment. People who double clicked on the
attachment allowed the code to execute. The code sent copies of itself to
everyone in the victim's address book and then started corrupting files on the
victim's machine. This is as simple as a virus can get. It is really more of a
Trojan horse distributed by e-mail than it is a virus.
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6.5 An Ounce of Prevention
Computer viruses implant instructions in other programs or storage devices and
can attack, scramble, or erase computer data. The danger of computer viruses
lies in their ability to replicate themselves and spread from system to system.
Few computing systems are immune to infection.
The following activities are among the most common ways of getting computer
viruses. Minimizing the frequency of these activities will reduce your risk of
getting a computer virus:
• Freely sharing computer programs and system disks, or downloading files
and software
• Downloading executable software from public-access bulletin boards or
web sites
• Using your personal disk space (e.g., floppy disks, flash disks) with
public computers or other computers that are used by more than one
person
• Opening email attachments from people you don't know or without first
scanning them for viruses
• Opening any email attachment that ends in .exe, .vbs, or .lnk on a
computer running Microsoft Windows
• Continually running your Windows computer as an administrator
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6.6 Signs of a virus infection
If your computer begins to act strangely, or if it stops being able to do things it
has always done in the past, it may be infected with a virus. Symptoms such as
longer-than-normal program load time, unpredictable program behavior,
inexplicable changes in file sizes, inability to boot, strange graphics appearing
on your screen, or unusual sounds may indicate that a virus is on your system.
However, it is important to distinguish between virus symptoms and those that
come from corrupted system files, which can look very similar. Remain calm
and objective, and rule out more standard causes before suspecting a virus.
6.7 How to avoid computer viruses
Prevention is a matter of caution and avoiding contact with unknown files, web
sites, and disks. It is usually the unwary who get computer viruses. Following
is a list of some recommendations for safe computing:
• Install virus detection software and keep the virus patterns up to date.
Antivirus programs perform two general functions: scanning for and
removing viruses in files on disks, and monitoring the operation of your
computer for virus-like activity (either known actions of specific viruses
or general suspicious activity). Most antivirus packages contain routines
that can perform each kind of task.
3. Run secure operating system and keep your operating system current with
the latest patches and updates. The writers of viruses and worms often
exploit bugs and security holes in operating systems and other computer
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software. Software manufacturers frequently release patches for such
holes.
4. Back up your files. Viruses are one more very good reason to always
back up your files.
Note: If you back up a file that is already infected with a virus, you can
re-infect your system by restoring files from the backup copies. Check
your backup files with virus scanning software before using them.
5. Keep your original application and system disks locked (or write-
protected). This will prevent the virus from spreading to your original
disks.
6. If you must insert one of your application disks into an unknown
computer, lock (write-protect) it first, and unlock your application disk
only after verifying that the machine is virus-free.
7. Check newly downloaded software thoroughly using reputable virus
detection software on a locked floppy disk for any signs of infection
before you copy it to a hard disk. This can also help protect you from
Trojan horse programs.
8. Quarantine infected systems. If you discover that a system is infected
with a virus, immediately isolate it from other systems. In other words,
disconnect it from any network it is on and don't allow anyone to move
files from it to another system. Once the system has been disinfected, you
can copy or move files.
2. You should make sure that Macro Virus Protection is enabled in all
Microsoft applications, and you should NEVER run macros in a document
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unless you know what they do. There is seldom a good reason to add
macros to a document, so avoiding all macros is a great policy.
Select the Macro option under Tool menu and click Security in
Microsoft Word and make sure that the High option is enabled, as shown.
3. You should never double-click on an attachment that contains an executable
that arrives as an e-mail attachment. Attachments that come in as Word files
(.DOC), spreadsheets (.XLS), images (.GIF and .JPG), etc., are data files
and they cannot damage (noting the macro virus problem in Word and
Excel documents mentioned above). A file with an extension like EXE,
COM or VBS is an executable, and an executable can do any sort of
damage it wants. Once you run it, you have given it permission to do
anything on your machine. The only defense is to never run executables that
arrive via e-mail. By following those simple steps, you can remain virus
free.
• What is a computer virus?
• Besides viruses, what are other types of destructive programs are there?
• How are viruses transmitted?
• How has the influence of the online world (the Internet, networks,
bulletin board systems, and e-mail) affected the world of viruses?
• Will you get in trouble if you report a virus?
• What can viruses and other destructive software do to your system?
• How do you prevent viruses?
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• How do you know if you have a virus?
• How do you stop a virus once you discover you have one?
• Why do people write viruses and other destructive software?
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Compendium for computer application