for the Students of University of Madras
HARAT SANCHAR NIGAM LIMITED
(A Government of India Enterprise)
RAJIV GANDHI MEMORIAL TELECOM TRAINING CENTRE
(ISO 9001:2008 Certified)
INTRODUCTION TO COMPUTERS
INTRODUCTION TO COMPUTERS
We are living in an informa
tion age dependent
upon digital information. Digital information is electronic information, the result of
computer processing. Every type of job relies upon getting information, using it,
managing it, and relaying information to others. Computers enable th
processing and storage of information.
Classifications of Computer
The capability of computer depends upon the amount of data stored in the main
memory, the speed of operation, the number of peripheral devices, amount and
types of programs
available for the use with the computer system. Accordingly,
computer can be classified as follows:
1.1.1 Mainframe computers
, the larger of the computers can literally fill a room.
These large computers
are used to fulfill the computing needs of large companies
and corporations and are also used in large telecommunications centers. They are
very powerful with huge amount of storage and processing capability. The
drawbacks to the mainframe computer for us
e as a personal computer are its size,
its immense amount of computing power, and its price, which can run into crores
was developed to serve the computing needs of smaller
companies and the larger departments of corporations
. It has essentially the same
functionality of the larger mainframe computer but on a smaller scale. The
mainframe was scaled into a smaller package with most of its functions remaining
and a little less storage and processing power, sold at reduced price.
advances in technology, today's minicomputer can fulfill the entire computing
needs of a small
sized company as well as serve as a very powerful
communications server. But mini computer are much too big, in terms of
and size, not to mention price, to be used as a personal
is the smallest one and is often seen on the desk therefore
is referred to as desktop. It has a good processing power, though not of the same
degree as of mini or ma
inframe, with a much smaller size, with affordable price and
is quite effective for personal uses.
Two further types of computer need mentioning i.e. Super Computer & Embedded
is an extremely powerful computer used mostly in
search and space, military and governmental applications. A super computer is
the costliest one and can cost crores of rupees. It is equivalent of thousands of
personal computers that share in the processing load to solve very large and
complex problems in
hours or days instead of weeks, months, or years. A
supercomputer is the largest and most powerful computer, sometimes equaling the
power of several mainframes combined.
is built into another device to control, monitor, or
e some activity for the device. Virtually all electronic devices have an
embedded computer built inside for example a microwave oven, modern televisions
etc. They have very small and single purpose processors. A personal computer also
has an embedded compu
ter in its microprocessor but it is a multifunctional device
capable of controlling more than a single process or activity.
1.2. Role of
As we hurtle towards the 21st century, we must accept the
inevitability of a computer revolution
in the near future. It is an
inseparable part of
development, as demonstrated by other countries. Computers are no longer luxury
or the sole property of the advanced countries. Their appropriate uses in India can
help us solve the unique problems of a dev
eloping country and bring about the
desired changes in increasing literacy, optimizing resources, inc
productivity and quality.
Already computers have become such an important part of our lives
in airports, banks, railway stations and
pped modern office. As
computer continues to proliferate in ever increasing numbers across large
segments of Government, business and industry, the common man is beginning to
believe hesitantly that computers can actually deliver a good par
t of the promise
that they had offered. Society is gradually accepting the fact that computers will
indeed change the manner in which the things are done
Computers can substantially save valuable man
hours by help
people through communication to mak
e reservation of tickets, operate their bank
accounts, to pay for electricity water and telephone bills, insurance premium and
also do routine shopping. Trains can be operated automatically by computers and
traffic signals be computer co
ordinate to produc
e best traffic patterns, increase
reliability and safety and generally provide for more efficient services.
The basic industry of India is 'agriculture'. In areas of agri
irrigation, computers are making possible better match
ing of soil char
and crop. This coupled with better use of resources like water, fertilizers and
sunlight and more precise prediction of monsoons can help India in increasing crop
Computer in health is bringing new hope for the sick. In areas
health and medicine, expert systems and data bases on blood groups availability,
eye banks medical history of patients etc, can bring about a marked improvement
in our health services. Expert system can help in more accurate diagnosis of
ital Information Systems' can help improve the efficiency of our hos
pitals reduce mortality and death
rates and in general provide better and speedie
health care to our people.
While this realization is gaining firmer ground in areas like the utility
ervices, railways, airlines, agriculture, health etc., as well as organization control,
there is area where the role of compu
ters as the prime agents of change has still
not been recognized. That is the area of education. In our country there are over
0,000 primary schools of which l/3rd are single
teacher schools. 64% of total
population of our country is illiterate. The number of illiterates at present is higher
than that at independence. To tackle a problem of such gigantic proportions, it is
al that a modern aids offered by Information Technology are made use of to
spread education to the rural areas where most of the illiteracy is concentrated.
Computer based lessons developed in various subjects by experts in that area
could be used to educa
te the masses. The computer is a rapidly evolving tool that
can now deal quite effect
ively with all fine forms of information that man deals with
for better education are
data, text, image, graphics and voice.
One thought can take place in our minds f
or a moment that 'the
computer will replace the teacher
that would be a suicidal thought. But we should
fully accept the reality that the computer will radically change the manner in which
cesses take place. The role of the teacher wi
ll undergo a
radical change. From being a mere "information dumping machine", the teacher
will once again rise to the height of being a mentor, philoso
pher and guide
developing, instilling values, ideas, creating challen
ges and nurturing feelings,
ents and empathy in young minds. In the wider prospective, these are what
are required for building a strong nation
intellectually spiritually and economically.
In the most important area of government administration, to enable
administration take the r
ight decision at the right time, accurate, relevant and up
date information should be made available to them. Modern computerized
communication network can significantly help bureaucracy cut its red tape.
Therefore, computers are synonymous with deve
appropriate computer usage and quality of life applications, India will be able to
effectively tackle its unique problems. The entire society will undergo a
transformation and what would emerge is a society that is more intellectually
nd which values its time, intellect and dignity. A society armed with
computer expertise can meet with confidence the exciting new India of tomorrow.
1.3 Inside Computers
1.3.1 Computer and its functions:
Computer is an electronic data processing device
capable of doing arithmetic
computations and other complex operations at a very high speed. The computer
does these operations on the basis of instructions given to it by a human being.
Thus a computer does not do anything by itself; it is only a tool and
does what you
ask to do. If you feed wrong information into it, the result also will be wrong.
Basic functions that a computer can perform are:
For different functions the computer has different component namely:
al Processing Unit
Arithmetic & Logic Unit
It consists of devices through which the data and/or program can be
communicated with the computer. The input device converts the data and/or
program from the hu
man readable form to the machine readable form i.e. into a
machine code. The various input devices in computer are:
Central Processing Unit
Control Unit, Arithmetic & Logical U
nit and Memory
Unit collectively act like the heart of the computer and are referred to as the central
processing unit. It is here that actual processing of data takes place on execution of
is responsible for overall control of
program execution. It receives
instruction from memory unit and on deciding the action to be taken, directs other
units of the computer to carry out respective functions. This unit, thus, performs
the following important functions:
Directing the flow of da
Executing instructions operations
after hardware and program errors
Control the sequence of the operation of various units.
Arithmetical & Logical Unit
All calculating functions like addition, subtraction,
multiplication, and division are c
arried out in this unit.
This unit stores instructions and/or data. This unit is also called
as main or internal memory. In this context two terms needed to be introduced i.e.
RAM & ROM.
(Random Access Memory) is the actual usable memor
y where the instructions
and data are made to reside during execution. The contents of this area exist there
as long as power is on.
(Read Only Memory) contains programs (of permanent nature) in machine
code which do not get wiped out even when power
goes off. The method of storage
of this memory is such that, it is neither erasable nor replaceable. Programs in this
area include operating system, monitor programs, etc.
Auxiliary or external memory is the additional memory used to supplement the
capability. Magnetic tape, floppy, disc, etc. are examples of this category.
The final result for a given problem residing in main memory can be
inscribed on an appropriate output device in the output unit of the computer. The
output can be
in either visual or audio or printer form. The output devices which
are in use today are:
Visual Display Unit
The various input and output devices of the computer are termed are termed as
The physical and tang
ible components of the computer i.e. those components
which can be touched and seen are called
It includes central
processing units consisting of resistors, capacitors, ICs etc. and peripherals
consisting of input devices and output devices.
all these devices are mere junks of there is no proper software. Software is the
program which gives life to the hardware. There are three major categories of
e are programs usually written by computer
manufacturers. These programs are inbuilt into the computer and are used to
govern the control of the computer hardware components, such as processors,
memory devices and input/output devices. They, in fact, act a
s an interface
between the user's programs and the computer components and facilitate in the
execution of programs.
This software is used to translate the programmer written
instructions into machine code instructions. This is machine
and is popularly known as assembler /compiler.
Application programs are user
written programs to perform
certain specific jobs. They are unique in their construction and can be used only
for identical jobs. MS Wor
d, Excel, etc. are common example of it.
Computers generally are of three type i.e. mainframe, mini and personal. What we
see on our desk is a personal computer. It has only been developed after the
mainframe and mini computer. Mainframe a
nd mini computers, though fast in
processing, were large in size, costly and needed experts for use and application.
But the Personal Computer (PC) has removed all these limitations and has made
the computing popular. Now we shall study the component of a
computer. In other words we shall study the hardware of a PC.
The hard wares of a typical PC include:
Visual display unit
Keyboard / Mouse
System unit, which contains the motherboard, disk drive, expansion card, and
Visual Display Unit (VDU)
The two general categories of PC visual presentation are monitor and display. A
has a Cathode Ray Tube (
) and looks something like a traditional
television set. On the other hand, a
is a flat
d Crystal Display
) that can be attached to a PC or hung on the wall. A display is really an
adaptation of the monitor, but because it uses different technology, they are treated
as two different components.
A monitor has some advantages over the displ
ay. It is bright, well
economical and produces excellent color and graphic qualities. A monitor uses the
same technology common to the television set. The monitor is basically a funnel
shaped glass tube (technically known as cathode ray tube) that
uses electron guns
to light up (technically known as
) phosphor elements on the back of display
glass. The lighted phosphorous blend to form images and movements and is shown
through the display of the CRT for the user to view. The user views the
osphorous through a single pane of glass, which is why the display is so bright
and why it is easily viewed from an angle.
But if there is limitation of space on a desk or worktable an LCD display is a more
suitable option than a CRT monitor. A typical CRT
monitor are 12 inch or more
from front to back, which can take a considerable amount of workspace on a desk.
panel LCD displays are typically only a few inches deep including its foot,
which makes them perfect for small desks or places where a large
would negatively impact the aesthetics or decor. Even the new PCs that are
integrated into the same package as a flat
panel display are only inches in depth.
panel LCD display are backlit, which means the light source of the display
through several layers of filters and glass before on see it. This is why LCD
displays appear to be less bright than a CRT
style display and less legible from an
angle. However, LCD displays are digital, which means they are able to reproduce
images more a
ccurately, especially colors.
The monitor and display can be found in different sizes. The most popular sizes are
inch and 21
inch. This is the size of the CRT or LCD
measured diagonally from a top corner to an opposite botto
m corner (in the same
way a television set is measured and marketed). The viewable size of CRT, however,
is a bit less than its nominal size for the front bezel (the plastic around the edge of
the display) covers up a small portion of the display.
es displayed on a monitor are created from a pattern of dots in much the
same way as the photographs in a newspaper.
are shaded lighter or darker so
that ones eyes can form a visual image from them. The CRT creates these dots from
the phosphor on the
back of its screen using masking methods that isolate each
dot so that it can be illuminated by an electron gun.
A monochrome, or single color, monitor has phosphor of only one color, so that
when the phosphor dots are illuminated, the text and the graphic
image is a single
color on a contrasting background. Typically, the background is black and the
display color is green, amber or white.
The image produced on a color monitor is created by illuminated small triangles of
phosphor dots called picture elemen
for short. In the CRT, one
the dots are red dots, one
third are green dots, and one
third are blue dots. These
different colored dots are interspersed evenly on the screen so that a dot of each
color can be grouped with a dot of each
of the other colors to form a triangle or
A color CRT has three electron guns that are used to light up the phosphors in
each pixel. The combinations and intensities used to illuminate the phosphors
define the image produced on the screen. The elec
tronic guns sweep over the pixels
from side to side, one row at a time, to create or refresh the displayed image.
LCD displays are of two different types: passive matrix and active matrix. A passive
matrix display has a layer of LCD elements on a grid (mat
rix) of wires. When
current is applied to the wire intersections, the diodes (pixels) are lighted. A passive
matrix refreshes the display by applying current to the pixels at a fixed rate. Active
matrix displays control each LCD element (diode) individuall
y with one or more
transistors that continually refresh each element of the display.
The most common input device is the keyboard. The keyboard allows a user to
communicate with the PC through keystrokes that represent character data and
Virtually every PC sold has a keyboard included as a part of its
standard package. In fact, most people take their keyboard for granted and rarely
even think about it.
Most keyboard layouts are still a variation on the key layout of a typewriter, at leas
for the alphabetic, numerical, and special character keys. However, keyboards also
include a variety of other keys that are dedicated to specific functions or are
assigned functions by the software running on the PC, such as a keyboard‘s
The mouse is a very natural, intuitive, inexpensive pointing device on a graphical
user interface like Windows. Two types o mouse in use today are:
In a mechanical mouse, the movement of a rubber ball
causes a pair of wheels to
spin that sensors detect to send data signal to the PC. Later modification came to it
and light emitting diodes were used to sense mouse movements and thus termed
A little modification of optomechanical m
ouse when a
finger wheel was attached on the top of it, typically between the two buttons i.e. left
click button and right click button. The wheel allows the user to scroll forward and
backward through a document in place of clicking on a window‘s scroll b
ar or using
the PAGE UP and PAGE DOWN keys or the cursor control arrow keys or the cursor
control arrow keys.
The optical mouse eliminates the mouse ball, replacing it with a optical sensors
that track the movement of the mouse against the ba
ckground of the mouse pad or
whichever flat surface it‘s on.
One real advantage to the optical mouse over the
optomechanical mouse is that it does not require internal cleaning. Because it has
eliminated all moving parts, the optical mouse does not pick up
dust and other
debris that could clog up the optomechanical mouse and require it to be regularly
cleaned. Another advantage is that, according to manufacturer claims, an optical
mouse is at least 33 percent faster and many times more accurate than an
1.3.3 Internal Hardware
The major components within a typical system case are:
Chipsets and Controllers
Hard Disks and Floppy Disks
e will discuss in brief each of these components.
The microprocessor is a multi function integrated circuit that is, in essence, the
computer. The processor, which is also called the central processing unit (CPU), is
made up of several part
s. These parts work together to carry out the instructions
and actions that translate to a word processing system or a game on the PC.
Microprocessor of Intel is very popular and has a very higher clock speed. The clock
speeds of the Pentium I processor of
Intel range from 60 MHz to 200 MHz and that
of Pentium IV range from 1.3 GHz to 3 GHz.
The primary parts of the CPU are Control Unit, Protection Test Unit, Arithmetic and
Logic Unit, Floating Point Unit, Memory Management Unit, Bus Interface Unit, The
fetch Unit, Decode Unit and Registers.
A motherboard (also known as a main board or system board) aggregates all of the
PC's primary system components on a single printed circuit board. In the
motherboard's single board design all the Pc's elec
tronic circuitry that provides the
conduit through which all operations flow is located on the motherboard.
The major components found in a typical motherboard are CPU slot and socket,
Chipset, Memory sockets, BIOS ROM, CMOS battery, Power connectors, I/O
Connectors and Expansion Slots.
The chipset is technically a group of chips that helps the processor and other
components on the PC communicate with and control all of the devices plugged
into the motherboard. The chipset controls the bits (data, i
nstructions, and control
signals) that flow between the CPU, system memory and over the motherboard's
bus. The controller chip also manages data transfers between the CPU, memory
and peripheral devices and provides support for the expansion bus and power
anagement features of the system.
A PC's BIOS (Basic Input / Output System) includes the programming to perform
three vital useful functions for the PC:
It boots the computer.
It validates the PC's configuration.
It provides an interface between the
hardware of the PC and its software.
ROM (Read Only Memory) is an electronic component. The data stored on ROM can
not be changed. Moreover it is
i.e. it keeps its content even without a
power source. This makes it ideal for storing the PC
's startup instructions and
CMOS memory is based on Complementary Metal Oxide Semiconductor technology
and requires only about one
millionth of an ampere to hold any data stored on it.
Using only a lithium battery, CMOS memory is able to
store the startup
configuration of a PC for many years. The term CMOS is still synonymous with the
PC's startup configuration data.
RAM (Random Access Memory) is used in the PC for its primary memory. RAM is
where all active programs and data are stor
ed to that they are readily available and
easily accessed by the CPU and other component of PC. When a program is
executed, a copy of the program from the hard disk is copied into RAM. Once it is
in RAM, the instructions that make up the program are passed
one at a time to the
CPU for execution. Any data that the program accepts or reads from a disk is also
stored in RAM. It is a volatile but very fast in accessing the data. For example
accessing data from a hard disk takes from 8 to 16 milli
second while t
data from RAM takes from 50 to 80 nano
second. The size of the RAM is measured
e.g. kilobyte or megabyte.
Cache memory is very fast computer memory that is used to hold frequently
requested data and instructions. A cache is a
ny buffer storage used to improve
computer performance by reducing its access time. The cache is commonly found
between RAM and CPU. To speed up the transfer of data and programs from the
hard disk drive to RAM, also, a disk cache is used.
Hard Disk & Flop
py Disk Drives
Hard disk and floppy disk are types of secondary storage, with the PC's RAM
providing its primary storage. Hard disk drive is electronic equipment which stores
the data on the hard disk of the system. Whereas floppy disk drive stores the dat
of the system on the floppies which are kept outside the system and helps in the
transfer of data from one system to another.
ROM Drive with Writer
ROM (Compact Disk Read Only Memory) Drive is a new invention and has
solved the problem of secondary
storage. A huge data can be stored on a single CD.
The technology used is same as that of audio CD. Earlier once the data stored on a
CD was not re
writable but now the data can be written, read and re
written on the
CD through the CD Drive.
Expansion cards are used to connect different peripherals (like ports providing
network connection, memory expansion etc.) of the computer to its motherboard.
The PC's power supply unit converts AC power from the wall socket to DC power f
the computer. Even the devise outside the computer case use DC power. In making
this conversion, the functions the power supply performs are conversion,
rectification, filtering, regulation, isolation, cooling, and power management.
Peripheral devices s
uch as printers, external modems and disk drive use Ac power
converters to convert AC power to DC power.
1.4 Operating Systems
An operating system is a collection of programs that is needed to start and operate
the computer system. It works mostly in the
background, specially when one start
the computer system, it is the operating system which takes over and does the
household routines on the computer system and hands over the computer to that
self for operation. Moreover it checks for the various commands
that are given to
the computer to ensure that nothing wrong is happening.
Operating system also acts as an interface between a user and the hardware of the
computer. It controls and coordinates the use of the hardware among the various
ms and thus acts as a Resource Manager.
We can thus summarize the functions of operating system as follows
Execution of program
Handling File System
Detection of errors
Allocation of resources
Information and Resource Protection
l these services are ensured by the functions provided by an operating system.
The functions offered by different operating system differs from one operating
system differs from one operating system to another, but more or less they provide
the same servic
es. Most commonly used operating systems are:
MS DOS (Micro
Soft Disk Operating System)
Microsoft's Disk Operating System, simply known as MS DOS had been the
prominent software for the running of the Personal Computer (PC).
Actually it was
the big factor in popularizing the PC. Starting with version 1.0 MS DOS has now
come to the version 7.
The operating system should always remain in the main memory. The process of
transferring the operating system to the main memory is know
operating system contains three files for booting viz.:
If the floppy contains these three files in the 0 track then it is called as booting
There is a program called Bootstra
p (Boot Program) in BIOS chip in the computer.
It does the following functions.
Testing the Hardware as per configuration
Search the OS and transfer the same i.e. it reads the boot sector, which
contains DOS boot record and then transfers the same to the m
The boot record copies the IO.SYS, which contains SYSINT. Once IO.SYS is loaded,
boot record is not required. The SYSINIT will take care of further action. Now
MSDOS.SYS is loaded. Now SYSINIT searches for the CONFIG.SYS file and then
same and gives instruction to MSDOS.SYS to act on CONFIG.SYS. The
SYSINIT instructs the MSDOS.SYS to load COMMAND.COM.
The COMMAND.COM contains the I/O operation and internal commands. It is the
command interpreter. After the loading of the COMMAND.COM th
AUTOEXEC.BAT file will be executed. Finally the prompt will be displayed on the
VDU indicating that the booting is successfully completed and now the PC is ready
to accept any command.
A command is something you use to instruct MS
DOS what to do. All com
are entered in the command line following the MS
DOS prompt. A command is
entered along with the necessary parameters and switches. So,
what is to be done (What to do)
to act upon what (Where to do)
how the command
is to be carried out (How to do)
DOS commands are divided into
Internal command are memory resident. They are available in
The external commands are available in the form of a file, whose
name is same as
the command with extension as either COM or EXE. Whenever the command is
issued the processor refers to the file and executes the command.
Windows is also a product of Microsoft. From Windows 95 to Windows xp it has
ral version with each newer version improved over the older. What makes
it different from the MS
DOS is that it is based on Graphic User Interface (GUI).
Here the user is not required to write a command in the command line as in the
MS DOS rather he can us
e different menus of commands available on the screen.
Moreover it is mouse compatible. So a user is required to click the mouse only to
access different commands.
Another feature of this operating system is that multiple works can be carried out
everal windows which can be operated simultaneously. For example,
while the system is copying the file from the computer to floppy one can also read
another file. This feature of window has made it much popular and time saving.
titasking operating system that is widely used as the master
control program in workstations and servers. The Open Group holds the trademark
for the UNIX name (spelled in upper case) on behalf of the industry and provides
compliance certification to the UN
Unix is written in C. Both Unix and C were developed by AT&T and freely
distributed to government and academic institutions, causing it to be ported to a
wider variety of machine families than any other operating system. As a result,
me synonymous with "open systems."
Unix is made up of the kernel, file system and a shell, which is the command line
interface with more than 600 commands for manipulating data and text. The major
shells are the Bourne shell (original), C shell and Korn s
Varieties of commercial applications run on Unix servers, and many Web sites run
under Unix. Over the years, there have been many different versions of the OS,
and, except for the PC world, where Windows dominates, almost every hardware
s Unix as its primary or secondary operating system. Sun has been
singularly instrumental in commercializing Unix with its Solaris OS (formerly
SunOS). HP, IBM, SCO and Digital (before it merged with Compaq) have also been
major Unix promoters.
A very popular version of the Unix operating system that runs on a variety of
hardware platforms including x86, Itanium, PowerPC and IBM's entire product line.
Linux is widely used as a server OS and is gaining ground in the desktop market.
In 1990, Fin
nish computer science student Linus Torvalds turned Minix, a popular
classroom teaching tool, into Linux, which is closer to the real Unix. Torvalds
created the kernel, and most of the supporting applications and utilities came from
the GNU project of the
Free Software Foundation. Many programmers have
contributed to the Linux/GNU system.
Linux is the most popular open source operating system in use now. Its source
code is available free of charge; however, Linux is distributed along with technical
and training for a fee from several vendors such as Red Hat Software
(www.redhat.com) and SUSE Inc. (www.suse.com). The distribution CD
include the complete source code as well as hundreds of tools, applets and utilities.
the storage media in PC systems operate on magnetic principles. Hard disk
is the largest external memory of a PC system. It can be classified as exchangeable
& fixed. It is attached to a PC system through an IDE(Intelligent Drive Electronics)
or SCSI(Small Computer System Interface) adapter port. It is available
in different capacities like 20 GB, 40 GB, 80 GB,100 GB etc.
A Hard Disk Drive is a sealed unit that a PC uses for non
volatile data storage.
Nonvolatile, or permanent storage, in thi
s case, means that the storage device
retains the data even when there is no power supplied to the computer. Because
the HDD is expected to retain its data until a user deliberately erases it, the PC
uses it to store its most crucial programming and data.
As a result, when the Hard
Disk fails, the consequences are usually very serious.
1.5.1 Hard Disk
A Hard disk drive contains rigid, disk
shaped platters, usually constructed of
aluminium or glass. A motor spins the platters at 5400 or 7200 rpm when the dr
is operating. In order to increase the amount of information the drive can store,
most hard disks have multiple platters and read/write heads.
Data is stored on the surface of a platter in sectors and tracks. Tracks are
concentric circles and sectors
shaped wedges on a track.
A sector contains a fixed number of bytes
say 256 or 512 bytes. Sectors are often
grouped together into clusters.
The identically positioned tracks on each side of every platter together make up a
cylinder. A HDD normall
y has one head per platter side, with all the heads on a
common carrier device, or
The process of low
level formatting a drive establishes the tracks and sectors on the
platter. The starting and ending points of each sector are written onto the platt
High level formatting then writes the file
storage structures like the file
table into the sectors. This process prepares the drive to hold files.
A Hard disk drive is designed to be used with more than one operating system.
ables a single HDD to run more than one type of Operating Syst
or it can enable a single Operating System to use the disk as several volumes or
Operating System assigns a drive letter or name.
1.5.2 Floppy Disk
Floppy disk is another
magnetic storage device. It is made of thin, flexible Mylar
plastic coated with magnetic material and protected by an envelop. Earlier, 5.25”
floppy disk with capacity 360 KB were in use. Nowadays 3.25” floppy disks are only
available in the market with c
On the basis of recording density and capacity of a sector, floppy can be classified
as single density and double density disk.
The major parts of a Floppy disk drive include:
: Located on both sides of a diskette, they
move together on
the same assembly.
: A very small motor that spins at either 300 or 360 rotations per
: This motor makes a precise number of stepped revolutions to
move the read/write head assembly to the proper tra
: A system of levers that opens the little protective window
on the diskette to allow the read/write heads to touch the dual
: Contains all of the electronics to handle the data read fr
written to the diskette.
CDROMs are used for storing large software packages and can contain all types of
multimedia data storing over 650MB of data. They are optical storage devices.A CD
is a simple piece of plastic about 1.2 mm thick a
nd 12cm in diameter. CD consists
of an injection
molded piece of clear polycarbonate plastic. Once the clear piece of
polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the
disc, to make the surface reflective. The colour of a CD
can be cyanine
yellow or azo
blue. Then a thin acrylic layer is sprayed over the
aluminum to protect it. The label is then printed onto the acrylic.
A CD has a single spiral track of data, circling from the inside of the disc to th
outside. The data track is approximately 0.5 microns wide, with 1.6 microns
separating one track from the next.
The track always circles from the inside of
the disc to the outside.
(often shortened to
) is the
, and maintaining the
. This source code is written in one or
. The purpose of programming is to create a set of
ctions that computers use to perform specific operations or to exhibit desired
behaviors. The process of writing source code often requires expertise in many
different subjects, including knowledge of the application domain,
1.6.2 Need for Languages:
, particularly a
languages can be used to create
that control the behavior of a machine
nd/or to express
The earliest programming languages predate the
invention of the computer
were used to direct the behavior of machines such as
. Thousands of different programming languages have be
en created, mainly
in the computer field, with many more being created every year. Most programming
languages describe computation in an
style, i.e., as a sequence of
commands, although some languages, such as those that support
, use alternative forms of description.
The description of a programming language is usually split into the two
(meaning). Some languages are defined
by a specification document (for exam
programming language is specified
Standard), while other languages, such as
5 and earlier, have a
that is used as a
A vocabulary and set of grammatical rules for instructing a
specific tasks. The term
usually refers tohigh
languages, such as
has a unique set of
(words that it understands) and a
level programming languages, while simple compared to human languages,
re more complex than the languages the computer actually understands,
. Each different type of
has its own unique machine
Lying between machine languages and high
level languages are languages
. Assembly languages are similar to machine languages,
but they are much easier to program in because they allow a programmer
for numbers. Machine languages consist of numbers only.
Lying above high
level languages are languages called
). 4GLs are far removed from machine
languages and represent the class of computer languages closest to human
Regardless of what language you use, you eventually need to
to machine language so that the computer can understand it. There are two ways
to do this:
for more information about these two methods.
The question of which language is best is one tha
t consumes a lot of time and
energy among computer professionals. Every language has its strengths and
weaknesses. For example, FORTRAN is a particularly good language for processing
data, but it does not lend itself very well to organizing large
Pascal is very good for writing well
structured and readable programs, but it is not
as flexible as the C programming language. C++ embodies powerful
, but it i
s complex and difficult to learn.
The choice of which language to use depends on the type of computer the program
on, what sort of program it is, and the expertise of the programmer.
1.6.3 Skills Needed In Programming
Programming does not represe
nt a theoretical subject like Biology, Physics,
Mathematics or Chemistry. Consequently it is not necessary to have an advanced
degree in order to do very well or rather become perfect at programming.
In comparison to a variety of so
called physical tasks s
uch as writing poetries,
singing, painting, gymnastics or rhyming, programming is not in need of special
innate talents or skills. So programming does not require strength, power,
condition or coordination. In order to do very well at programming it is nec
be careful and have a special capacity like craftsmanship.
Things that are required for doing very well at programming are attention to detail,
specialized and technical knowledge, stupidity, good memory and the specific
ability to think in an ab
stract way in both all respects and every sense.
Attention to detail
Considering the matter of programming details are
playing a significant and very important role. So if the respective
programming language says it is necessary to declare and specify var
before using them, you have to do so. However, if the programming language
requires the usage of parentheses, brackets and square brackets, you have
to do so as well.
Specialized and Technical knowledge
If you want to do very well at
u should have a profound specialized and technical
knowledge considering programming languages, programming in
, servers, etc. Be sure that you possess expert know
how considering all things that have to do with web sites and web
pment as well as other related issues such as for instance
configuration, optimization and practical use of both servers and web
You certainly will not believe, but in spite of all it is true that
computers are incredibly stupid. Fact i
s that computers do only those things
you tell them to do
no more, no less. When it comes to programming in
connection with the so
called stupidity of computers it is helpful to think as
stupidly as computers do.
Programming requires a very
good memory. Because of the
fact that there are loads of important things and details to remember, it is
essential to be able to memorize basic and relevant programming facts.
Some of these are for instance the syntax of the respective programming
, prewritten functions and parameters, variables and specific
functions, bugs you have had in the past and you want to avoid in the
future, etc. So the more of this basic know
how and details you are able to
keep in mind, the more successful you will be at
Ability to think in an abstract way
The specific ability to think in an
abstract way on several levels as well as in all respects is certainly the most
essential skill in programming. Strictly speaking computers do represent one
of the most
extensive and complex systems of all which do require knowing
and memorizing every single basic aspect and function of this system at all
levels as well as in all respects.
The term network usually means a set of computers and
erals (printers, modems, plotters, scanners, and so on) that are connected
together by some medium. The connection can be direct (through a cable) or
indirect (through a modem). The different devices on the network communicate
with each other through a pre
defined set of rules called the protocol. Computer
networks allow people and machines to communicate, using a number of services.
The networking of computers become essential for two reasons:
Networks offer th
e capabilities of multi
user access to the organisational Data.
Shared files may exist in one location with multiple people accessing them or
updating parts of them. Database applications are found in virtually every
computerised organisation. Transmitting
mail is one method of sharing data.
This avoids the face to face contact of people and improves the faster data flow.
Not only data files may be shared, but executable files may be shared as well. When
a user invokes an executable file on a network ser
ver, a copy of it is transmitted
over the network into the memory of the local user's workstation. That is where the
actual execution takes place, not on the file server
One of the distinct benefits of networking is the ability to share
example Laser Printer is costly and for a small office one can not afford to purchase
more than one printer to attach for each PCs. Instead one Laser Printer can be
shared by more PCs when the PCs are connected through Network. The abilit
sharing printers and disk space has been the driving force behind many companies
The Line configuration defines the attachment of Network devices to a link. There
are basically two type of line confi
gurations are there, they are:
Point to Point
The Point to Point line configuration provides a dedicated link between two Network
devices. The entire band width is available for transmission.
The Multi point Line configuration is also called
Multi drop. In Multi Point Line
configuration more than two devices share the media. The bandwidth is shared
either Spatially or Temporally. If several devices can use the link simultaneously it
is a spatially shared line configuration. If the user must ta
ke turns, it is a time
shared Line configuration
The Physical layout or how the transmission media are wired together is known as
the Physical topology.
There are different type of topologies used in the Network they are:
The Bus Topology
The bus network is the simplest, comprising a single main communications
pathway with each device attached to a single transmission media.
A bus topology is a multipoint line configurati
on. A bus topology uses a single
transmission media to which network devices are attached. This single
transmission media acts as backbone. Because all workstations share this bus, a
workstation checks for any information that might be coming down the back
before sending their messages. All messages pass the other workstations on the
way to their destinations. Each workstation then checks the address of each
message to see if it matches its own.
The primary advantage of a bus network is that it allows f
or a high
Another advantage of the bus network is that it is usually immune to problems.
Ends are terminated with a terminator called Head End to avoid signal reflection.
Advantages of a BUS Topology
Easy to connect a computer or peripheral to
a linear bus.
Requires less cable length than a star topology.
Disadvantages of a Bus Topology
Entire network shuts down if there is a break in the main cable.
Terminators are required at both ends of the backbone cable.
Difficult to identify the prob
lem if the entire network shuts down.
Not meant to be used as a stand
alone solution in a large building.
Ring topologies consist of several nodes joined together to form a circle. In a ring
topology each device has a dedicated point to poi
nt line configuration only with the
other two devices on the either side of it. Ring consists of series of 150 Ω shielded
twisted pair cable connecting each station to its neighbour. Output port of one
device is connected to input port of its neighbour.
Messages move from one node
to the next, in one direction only. When a node receives a message that is
addressed to itself, the message is copied and sent back with a modification that
indicates it was received. Data was transmitted Uni
d the ring.
Each workstation acted as a repeater, accepting and responding to packets
addressed to it, and forwarding on the other packets to the next workstation
―downstream.‖ (i.e the frame is passed to each station in sequence, where the
frame is exami
ned, regenerated and then passed to the neighbour).
Multi Access Unit
A disabled or disconnected node may block the Ring. To avoid this an
automatic switch will by pass the faulty NIC. Once the
node comes live it will be
put in to the Ring. For practical purpose these switches are combined into a
centralised devices called Multi Access Unit (MAU). The Multi Access Unit will have
multiple ports to connect the devices.
The benefit of
such LANs was that response time was fairly predictable.
The more devices there were in the ring, the longer the network delays.The entire
network could be completely disabled if one of the workstations failed.
The star topolo
gy uses a central device with drop cables extending in all directions.
Each networked device is connected point
point to the central device, or hub. In
Star topology, each node has a dedicated Point to Point link only to the Hub. The
devices are not dir
ectly linked. All messages in a star topology must go through the
central device (Hub) before reaching their destination. It also acts as a repeater for
the data flow. This configuration is common with twisted pair cable; however, it can
also be used with
coaxial cable or fibre optic cable.
Advantages of a Star Topology
Easy to install and wire.
No disruptions to the network then connecting or removing devices.
Easy to detect faults and to remove parts.
Disadvantages of a Star Topology
Requires more ca
ble length than a linear topology.
If the hub or concentrator fails, nodes attached are disabled.
More expensive than linear bus topologies because of the cost of the
The protocols used with star configurations are usually Ethernet or Loc
Token Ring uses a similar topology, called the star
In tree topology devices are connected to a secondary hub and that in turn
connected to central Hub. A tree topology combines characteristics of linear bus
and star t
opologies. It consists of groups of star
configured workstations connected
to a linear bus backbone cable. Tree topologies allow for the expansion of an
existing network, and enable schools to configure a network to meet their needs.
Advantages of a Tree
point wiring for individual segments.
Supported by several hardware and software vendors.
Disadvantages of a Tree Topology
Overall length of each segment is limited by the type of cabling used.
If the backbone line breaks, the entire s
egment goes down.
More difficult to configure and wire than other topologies
Mesh topology is uncommon today because of its sheer impracticality. In a mesh
topology system, every node is connected to every other node. The pervading
t behind this is to offer the maximum amount of reliability for data transit
A computer virus is a program that spreads by first infecting files or the system
areas of a computer or network router's hard drive and then mak
ing copies of itself.
Some viruses are harmless, others may damage data files, and some may destroy
files. Viruses used to be spread when people shared floppy disks and other portable
media, now viruses are primarily spread through email messages.
orms, viruses often require some sort of user action (e.g., opening an email
attachment or visiting a malicious web page) to spread.
A virus is simply a computer program
it can do anything that any other program
you run on your computer can do. Some virus
es are designed to deliberately
damage files, and others may just spread to other computers. A worm is a type of
virus that can spread without human interaction. Worms often spread from
computer to computer and take up valuable memory and network bandwidth
which can cause a computer to stop responding. Worms can also allow attackers to
gain access to your computer remotely.
A Trojan horse is a computer program that is hiding a virus or other potentially
damaging program. A Trojan horse can be a program tha
t purports to do one action
when, in fact, it is performing a malicious action on your computer. Trojan horses
can be included in software that you download for free or as attachments in email
Most viruses, Trojan horses, and worms are activated
when you open an
attachment or click a link contained in an email message. If your email client
allows scripting, then it is possible to get a virus by simply opening a message. It's
best to limit what HTML is available in your email messages. The safest w
ay to view
email messages is in plain text.
Most users get viruses from opening and running unknown email attachments.
Never open anything that is attached to an email message unless you know the
contents of the file. If you receive an attachment from a fa
miliar email address, but
were not expecting anything, you should contact the sender before opening the
attachment. If you receive a message with an attachment and you do not recognize
the sender, you should delete the message.
Selecting the option to view
your email messages in plain text, not HTML, will also
help you to avoid a virus.
Tips to avoid virus:
virus software from a reputable vendor. Update it and use it
In addition to scanning for viruses on a regular basis, install an
scanner (included in most anti
virus software packages) and configure it to
start each time you start up your computer. This will protect your system by
checking for viruses each time you run an executable file.
Use a virus scan before you open
any new programs or files that may
contain executable code. This includes packaged software that you buy from
the store as well as any program you might download from the internet.
If you are a member of an online community or chat room, be very careful
bout accepting files or clicking links that you find or that people send you
within the community.
Make sure you back up your data (documents, bookmark files, important
email messages, etc.) on disc so that in the event of a virus infection, you do
e valuable work.
Hacking is the practice of modifying the features of a system, in order to
accomplish a goal outside of the creator's original purpose. The person who is
consistently engaging in hacking activities, and has accepted hacking
as a lifestyle
and philosophy of their choice, is called a
is the most popular form of hacking nowadays, especially in
the field of computer security, but hacking exists in many other forms, such as
phone hacking, brain hacking, et
c. and it's not limited to either of them.
Due to the mass attention given to
hackers from the media, the whole
hacking term is often mistaken for any security related cyber crime. This damages
the reputation of all hackers, and is very cruel and
unfair to the law abiding ones of
them, from who the term itself originated. The goal of this website is to introduce
people the true philosophy and ethics of hackers, hopefully clearing their name and
giving them the social status they deserve.
hods for Hacking Computer Terminals(Servers):
This comprises of either taking control over terminal(or Server) or render it useless
or to crash it.. following methods are used from a long time and are still used.
1.Denial Of Service
attacks give hacke
rs a way to bring down a network without gaining internal
DoSattacks work by flooding the access routers with bogus traffic(which
can be e
mail or Transmission Control Protocol,
Sniffing refers to the act of intercepting
packets. This interception can happen
through simple eavesdropping or something more sinister.
Spoofing is the act of sending an illegitimate packet with an
(ACK), which a hacker can guess, predict, or obtain by
4. Viruses and Worms
Viruses and worms are self
replicating programs or code fragments that attach
themselves to other programs (viruses) or machines (worms). Both viruses and
worms attempt to shut down networks by flooding them with massive amount
bogus traffic, usually through e
5. Back Doors
Hackers can gain access to a network by exploiting back doors administrative
shortcuts, configuration errors, easily deciphered passwords, and unsecured dial
ups. With the aid ofcomputerized
hers (bots), hackers can probably find any
weakness in the network.
6. Trojan Horses
Trojan horses, which are attached to other programs, are the leading cause of all
ins. When a user downloads and activates a Trojan horse, the software can
e full control over the system and you can remotely control the whole
system.. great..!!! They are also
Consider the situation, everything you type in the system is mailed to the hacker..!!
dn't it be easy to track your password from that..
functionallities.. So next time you type anything.. Beware..!! Have already
and ways to protect yourself from them..
8. Social Engineering
his was one o
f the oldest trick to hack.. Try to convince your user that you are a
legitimate person from the system and needs your password for the continuation of
the service or somemaintainence.. This won't work now since most of the users are
now aware about the Sc
am.. But this Social
concept is must for you to
have to convince victim for many reasons..!!!
This is another type of
keylogging, here you have to bring the user to
created by you resembling the legitimate one and get him
to enter his
password, to get the same in your mail box..!! Use social
10. Fake Messengers
So its a form of
in the application format.. getting user, to enter
info in the software and check your
in short, is a comprehensive word processing software package.
It provides all the features of a most advanced electronic typewriter. In addition to
these, many other features are also available in
Some of the importa
nt features are given below. You can
Insert characters, words, sentences, paragraphs or pages of text anywhere in
the opened file.
Alter, insert, delete, or correct any character, paragraph, page at any time in the
Move a selected portion of text to
any location in the file using a few keystrokes
or mouse clicks.
Copy a section of text and insert it in any location using a few key strokes or
Find and replace a character, a word or phrase repeatedly.
View the document in its true form or
in miniaturized form.
Insert pictures and objects in the existing text.
Check the spelling and correct the wrongly typed words.
Check the grammar in a portion or entire document in the file.
Check the words with similar and opposite meaning for a given wor
Create a multi column document.
Introduce numbering and bullet in the document.
Insert a table.
Use different fonts of different styles for a part/entire file.
Superscript or subscript.
Draw shapes using available drawing tools.
Create borders and shade
Create headers and footers.
Resize the pages and so on.
A typical Word screen looks like Fig
Elements of Word Window
Word is built around a set of interactive windows (rectangular on
through which you communicate with the
Figure 1.1 shows two windows on the screen, one nested within the other. They are
Application window and
Application window is the outer window that contains the
workspace for all word
processing procedures. Ap
plication window frames the
entire screen of the monitor. You use it to communicate with the Word program.
Document window sits within application window. It is the
inner window where the text and images are entered.
Control Menu Box
his appears at the top
left corner of the window. When
clicked, it displays menu options to move, resize, close a window, or switch to other
They are located in the upper
right corner of the window. They are
called minimize but
ton, maximize/resize button, close button.
is located to the left of the resizing button. A click on it
reduces a Window to a button on
button, when clicked enlarges a program window
the entire screen or enlarge a document window to increase the work area
inside an application window.
Clicking on this button closes the window.
Title Bar is the band displaying the name of the application. Title bar is
of the application window. The inner window displays the contents of the
current document. Title bar displays the name of the opened document as
Document1. If you open one more document, the name of that document will be
displayed as Document2. When you sa
ve the documents,
appears and now you can opt for same name or a new one.
It contains different menus located below the Title bar. You can select
any of the options by clicking on it or pressing
key and then the underlined
phabet (Hot key). Refer figure 1.1.
When you click on a menu, a list of options
drops down. From it select any option by clicking on it. If an item appears dimmed
(usually in gray shade), it means that it is not available for use.
bar is usually located below the menu bar. It contains the
tools that are used very frequently while working with the documents. Each tool is
activated by clicking on its icon. See fig 1.1
This toolbar contains drop down menus for diffe
headings, types and sizes of fonts, borders and shades and also options of text
attributes, text alignments, bullets and indents. See fig.1.1.
Ruler contains scales that indicate the tabs, indents, and margin/paragraph
settings for the line/par
agraph in which the insertion point is currently positioned.
The settings of current paragraph may be quickly changed through the use of the
mouse and the ruler.
It is the vertical blinking line in the document window that
t location and where the next text entry or graphics will be
It is the shape of the mouse pointer when it navigates within the
text area of the document window. (The pointer will take different shapes
depending on its location in
window and the
It is the bar at the bottom of the
window that includes the page
number; section number, current page / total pages, the position of the insertion
point in inches, the current line
number and column number, current modes in
which Word runs.
They are the bars along the sides and/or bottom of a window, a dialog
box, or a list. They indicate that there is more information to be seen by scrolling.
To scroll through a docume
nt content, click on the beginning or end arrows located
on the scroll bar, or drag the scroll box slowly along the bar. The location of the
scroll box on the bar indicates the position of currently displayed information in
relation to the entire document.
The files in Word normally are called documents and
is the extension attached
by the system to the name of a Word file
2.1.1 Opening a Document
In File menu,
for opening a new document.
for the existing document
Otherwise the resp
ective icons in the standard tool bar can be clicked.
If you click
dialog box appears. In that, choose blank document (in
tab option). Click
. A blank document is opened with its name as
Document1, say, on the title bar. While saving
will appear. Choose the drive/folder/file‘s name and then click on the
The document will be saved with this new name.
If you click
in the file menu,
dialog box appears. Choose the
to be opened and click on the
button. The particular
document will be opened.
2.1.2 Saving a Document
As you enter information into a new document, the information is temporarily
stored in the computer‘s memory. The computer‘s memory will be erased wh
computer is turned off (or when you exit from your program). Saving the document
as a file on a disk provides a permanent copy of the document. A saved file can be
recalled later and its contents can be edited and can then be saved with
s included in it.
When you save a document as a file, you must give a name to it and specify the
location (drive and folder) where the file is to be stored.
Complete the following steps to save the current document.
Click on the
button on the
to display the
(see fig 2.2)
Locate the blinking insertion point in the
text box. Type the name
CTTC and do not press
Find the Drives‘ list in the
text box. Drop down the menu to choose the
either on the name of the drive shown in the
textbox, or on the drop
down arrow. Choose one from the list.
If necessary, use the scroll bar to select the name of the drive.
Locate the directory from the list below the Save in text box. Click on t
Click on the Save button to save the file.
After the file has been saved, note that the title bar on the window now reads
Modifying and Saving the Document
You have saved the document as
But still the
document is open. Make some changes or go to the end of the
document by pressing