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Computer – History
Computer through the Ages
We give below an overview of the developments which have taken place upto the time when 1st
Generation computers came into existence.
These are milestones which played some role later on
towards our achievements in the present day computer age.
16th Century
Abacus. This is considered as the first baby
step towards computers
Johan Napier
Napier’s Bones
Blaise Pascal
First Calculating Machine
Gottfried Von Leibntiz
Calculator (Modified Pascal’s machine)
Joseph Jacquard
Card of holes for weaving patterns
Charles Babbage
Difference Engine and Analytical Engine
Herman Hollerith
Howard Aitken and Grace Hopper
Dr John Vircent Atanassoff
ABC (Atanassoff-Berry-Computer)
JP Eckert and JW Mauchly
ENIAC (Electronic Numerical and Calculator)
H Goldshine, AW Burks and Johan
Von Neumann
Stored Program Concept
Lady Ada
Tabulating machine using punch
Binary number System
Johan Von Neumann
EDSAC (Electronic Delayed Storage
Automatic Computer)
Moor School in USA
EDVAC (Electronic Discrete Variable
Automatic Computer)
Eckert and JW Mauchly
UNIVAC-1 (Universal Automatic Computer)
Computer – Fundamentals of Computer
Binary System – Bit vs Byte
What is Binary System :
A system in which information can be
expressed by combinations of the digits 0 and 1. The modern day origin of this can be
traced to late 1930s, when Claude Shannon showed that it was possible to carry out
logical operations by assigning the number 1 to “true” and 0 to “false” while using switches
which were closed for “true” and open for “false,”.
What is Bit? Or What is Bits ? : The term
or bits means “binary digit“, meaning 0 or 1 in binary numbering. . Thus, we can say
that it is the smallest unit of information which can be manipulated by a digital machine.
(While writing in short form we merely use a lowercase b to represent bits). With two bits,
you can have four different states (2*2):
With 3 bits, you can have eight different states (2*2*2), and so on.
bits, it is possible to represent 2n values.
Thus, for a group of n
What is Byte? : The byte is a unit of information composed of 8 bits. It can
be used to store, among other things, a character, such as a letter or number. (While
writing in short form we merely use an uppercase B to represent a byte).
For a byte, the smallest number possible is 0 (represented by eight zeroes, 00000000), and
the largest is 255 (represented by eight ones, 11111111), making for 256 different possible
The data and instructions (code) that a CPU uses are coded into bytes. For example, capital
letter „A‟ in ASCII (PC) code is byte 0100 0001. A lower case „a‟ is byte 0110 0001.
A 16-bit unit of information is usually called a word.
A 32-bit unit of information is called a double word (sometimes called a dword).
Tips :
Bit Vs Byte :
A bit is always represented by a small “b”, a Byte is always represented by a large
It has become common practice to use bits in reference to interface speeds and bytes in
reference to memory and storage capacities.
Kilobytes and Megabytes :
Till 1998 , the following system for presenting various values was prevalent
(Some softwares still use the following system)
One kilobyte (kB) = 210 bytes = 1024 bytes
One megabyte (MB) = 220 bytes = 1024 kB = 1,048,576 bytes
One gigabyte (GB) = 230 bytes = 1024 MB = 1,073,741,824 bytes
One terabyte (TB) = 240 bytes = 1024 GB = 1,099,511,627,776 bytes
However, in December 1998, , the International Electro technical Commission weighed in on
the issue and issued new guidelines which are known as IEC‟s standardised units.
One kilobyte (kB) = 1000 bytes
One megabyte (MB) = 1000 kB = 1,000,000 bytes
One gigabyte (GB) = 1000 MB = 1,000,000,000 bytes
One terabyte (TB) = 1000 GB = 1,000,000,000,000 bytes
The earlier system of representing bytes has
been redefined by IEC and is known as binary kilo (kibi), binary mega
(mebi), binary giga (gibi), and binary tera (tebi).
They are defined as:
One kibibyte (kiB) is worth 210 = 1024 bytes
One mebibyte (MiB) is worth 220 = 1,048,576 bytes
One gibibyte (GiB) is worth 230 = 1,073,741,824 bytes
One tebibyte (TiB) is worth 240 = 1,099,511,627,776 bytes
Computer – Basic operations and
Computer Overview – Basic Concepts
What is a computer ? Define a Computer ?
A computer is an electronic device, which can compute and process data as per the
programmed set inside it.
However, these days the term is mostly used to refer to the
“Desktop” and “Laptop” computers that are used by most of us.
If you have seen inside a
computer, you must have noticed that it is not a single part machine.
These machines
(Desktop and laptops) are also popularly known as Personal Computers or PC.
computer consists of number of technical parts which are assembled in the required
Broad Categories of Computers :1.Based on Uses :
1.1 Analog Computer : It measures pressure, temperature, length, etc, of physical
quantities and converts into its numerical values. They are mainly used for scientific
and engineering purposes.
1.2 Digital Computer : It is used in counting of numbers, words or other special
symbols. It is also used in fuel control of automobiles and banking processes.
1.3 Hybrid Computer : It is the combined form of analog and digital
computer. Information is continuously converted into data that are received in the
form of input. Output may be in form of analog and digital. They are used in factories
and machines.
2. Based on Sizes : computers are also classified based on their size viz :
2.1 Micro Computer : It is the smallest computer in which ALU and CPU are based
on the same chip.
2.2 Personal Computer : It is single user system used generally in homes and
small businesses. Desktop and Laptops are examples of PCs, as these are best for
day to day small operations.
2.3 Mini Computer : It is more powerful than micro computer and can be used by
many users at the same time. It processes data very fast.
2.4 Main Frame Computer : They are giant in size and of highly storage capacity.
They can process an ample amount of data very rapidly. They are used in banks,
large organization and public sectors.
2.5 Super Computer : They are capable of processing the huge amount of data in
fraction of seconds. They are used in very complex calculation.
What are the Major Parts of the Computer :-
Central Processing Unit (popularly known as CPU) – it consists of different technical
parts like processor, motherboard, hard disc, RAM, CD Drive and cabinet with SMPS.
What are major accessories of the computer system ?
In addition to the above referred major components of the computer, we find the following
accessories attached to most of the computers :
Explain the concept of CPU:
Central Processing Unit or CPU is considered as the brain of computer.
CPU consists of
electronic circuits that interpret and execute instructions. It communicates with the input,
output and storage devices. CPU, with the help of memory, executes instructions in the
repetition of machine cycles. The speed of computer is measured in megahertz, MHz. A
MHz is a million machine cycles per second. A personal computer of 500 MHz has a
processor capable of handling 500 million machine cycles per second. Another measure of
speed is gigahertz (GHz), which means a billion machine cycles per second.
Explain the concept of Memory – RAM / ROM :
Memory or internal memory or primary storage works with the CPU to hold instructions and
data in order to be processed.
after being input.
It is in the memory that data and instructions are placed
(a) Moreover, the information is also placed in memory after processing so as to be
returned to an output device.
This kind of memory holds data only temporarily till electrical
current flow continuously. If current is interrupted, data is lost. Random Access memory
(popularly known as RAM) is an example of this kind of memory.
when we switch off the computer, the data is lost.
Thus, in this memory
The users access data in RAM memory
randomly as per needs. RAM can be erased or written over at will by the computer
(b) Another kind of memory is Read Only Memory (ROM). It contains prorams and data
that are permanently recorded when the computer is manufactured. It is read only and is
used by the processor. It is permanent in nature. and can not be altered or deleted by the
Thus, we can say that RAM is like a slate where you can write something for immediate
reference and then wipe / change data by adding or deleting when it is not needed, but
ROM is like a printed book, where once the text is printed then it cannot be altered.
(c) Secondary memory is also known as external memory or storage. It consists of Hard
Floppy Disc (now a days out of fashion) , CDs and DVDs as well as pen
drives. External device consists of more storage space and most dynamic in terms of
storing data.
Memory is measured in bytes. A byte is usually made up of 8 bits and represents one
character – a letter, digit or symbol.
The number of bytes that can be held is a measure of
the memory and storage capacity. Bytes are usually measured in groups of kilobytes,
megabytes, gigabytes and terabytes.
What are the Functions of the major components / accessories of the compute
system:CPU is the main unit of processing data, a mother borad is an electronic circuit for different
functions, hard disc is for storing the data, CD drive is to read and write data on CDs
(compact discs).
Monitor is for displaying the data, and is also popularly known as screen
or display unit. Keyboard is used to input the data.
Mouse is a pointing or selection
unit. Speakers, we all know, are used to hear the sound / music. Printer is used to take
the print of the data from the computer system. Scanner is used to scan and then store the
image / pictures in the computer. Modem is used to connect to internet.
File Extensions and Rules
File Extensions
File extensions are an important part of the name of a file.
Most of the software open a file
with a fixed name of file extensions. In case file extension is changed arbitrarily, the file
may not open in the desired software and / or may termed as corrupted and thus data may
be lost forever, if the user does not know how to set the same right. Let us first understand
basic concepts about Folders, Files and their extensions :What are Files / Folders / Directories :
Let us now learn about certain basic operations we need to do whenever we work on a
computer. Suppose, we have created some document i.e. we have typed some document,
then at the end of it, we would like the same to be saved for future reference or take print
out. In order to save a new document or file, you must first choose the Save command.
Most modern software place this command in a menu which you can access with the mouse
button or Alt key. When one such document is saved it is called a file. While saving the
document, it will ask you about the name you wish to give to this new document. Alongwith
giving a name to this file, the user has a choice to decide as to where such a file should be
saved. Such files can be saved within a Folder or Directory. Thus while giving a new name
to the file, users must also choose a directory and/or disk to store the file in. Some software
programs will automatically save files in specific directory that is created when the program
is installed (default settings).
Modern software place this command in a menu which you can access with the mouse
button or Alt key. When one such document is saved it is called a file. While saving the
document, it will ask you about the name you wish to give to this new document. Alongwith
giving a name to this file, the user has a choice to decide as to where such a file should be
saved. Such files can be saved within a Folder or Directory. Thus while giving a new name
to the file, users must also choose a directory and/or disk to store the file in. Some software
programs will automatically save files in specific directory that is created when the program
is installed (default settings).
Thus, a folder or directory can hold any number of files.
Sometimes, we install new software on our computer. In such cases also, the setup
executable file automatically creates new directories / folders and stores all the software
files in such newly created folders / directories.
Thus, we can say that user can create and delete directories or folders as the need arises.
Older operating systems require that the directory be emptied of files before it can be
deleted. When deleting / removing a directory, user must always check that no important
files is left in such directory or sub-directory. You should delete the directory only after
ensuring that it doesn‟t contain files you still need.
You can easily move files from one folder or directory to another, through either the use
menu commands or drag & drop using the mouse or a file utility
On the disk (it can be your hard disk, our floppy disc, CD or Pen Drive) you can create any
number of directories / folders – each of such directories / folders can contain number of
files. Moreover, These directories or folders could be compared to a filing cabinet. All files
are stored in a directory / folder. Most hard disks have many directories or folders and files
can be stored in any of them.
Directories can have sub-directories and sub-sub-directories many levels down. The
directory immediately below the current directory is called the child directory. The directory
immediately above the current one is called the parent directory. The top of the directory
structure is called the root directory.
Some common rules are:
• All files are saved on a disk or storage device.
• A disk is usually broken up into directories and sometimes into partitions.
• A directory or folder is a way of keeping like files in a common area.
Rules for File Names and Extension
Computers using DOS 6.X or older followed the 8.3 rule i.e. a filename can only be 1 to 8
characters long followed by a 1 to 3 character extension separated by a dot. Three
character extensions are common because of this.
Modern operating systems allow computer users to use filenames up to 256 characters. Mac
users, Windows 9X & NT/2000 and UNIX/LINUX (along with a few other) use long file names
but names using over 32 characters get unwieldy. It is better to use a directory or folder to
help describe them and keep common files together with shorter filenames.
Many modern software programs (applications) add their own extension to filenames. These
extensions allow operating systems to recognize certain filenames and associate (match)
them to the program that created it.
File Types, Appropriate Extensions And Software Used to Open Such Files
Type of File
Used By Which Software
3D Image Files
Rhino 3D Model
3D Image Files
QuickDraw 3D Metafile
Audio Files
Advanced Audio Coding File
Audio Files
Audio Interchange File Format
Audio Files
Interchange File Format
Audio Files
Media Playlist File
Audio Files
Audio Files
Audio Files
MP3 Audio File
Audio Files
MPEG Audio File
Audio Files
Real Audio File
Audio Files
Real Audio Media
Audio Files
WAVE Audio File
Audio Files
Windows Media Audio File
Backup Files
Backup File
Backup Files
Norton Ghost Backup File
Backup Files
Backup File
Backup Files
Original File
Backup Files
Temporary File
Compressed Files
Debian Software Package
Compressed Files
Gnu Zipped File
Compressed Files
Mac OS X Installer Package
Compressed Files
WinRAR Compressed Archive
Compressed Files
Self-Extracting Archive
Compressed Files
Stuffit Archive
Compressed Files
Stuffit X Archive
Compressed Files
Zipped File
Data Files
Lotus 1-2-3 Spreadsheet
Data Files
Comma Separated Values File
Data Files
Data File
Data Files
Database File
Data Files
Dynamic Link Library
Data Files
Microsoft Access Database
Data Files
PowerPoint Slide Show
Data Files
PowerPoint Presentation
Data Files
Structured Query Language Data
Data Files
Microsoft Works Spreadsheet
Data Files
Microsoft Excel Spreadsheet
Data Files
XML File
Developer Files
C/C++ Source Code File
Developer Files
C++ Source Code File
Developer Files
Java Source Code File
Developer Files
Perl Script
Disk Files
Mac OS X Disk Image
Disk Files
Disc Image File
Disk Files
Toast Disc Image
Disk Files
Virtual CD
Encoded Files
Macbinary II Encoded File
Encoded Files
BinHex 4.0 Encoded File
Encoded Files
Multi-Purpose Internet Mail Message
Encoded Files
Uuencoded File
Executable Files
Mac OS X Application
Executable Files
DOS Batch File
Executable Files
Common Gateway Interface Script
Executable Files
DOS Command File
Executable Files
Windows Executable File
Executable Files
Program Information File
Executable Files
VBScript File
Executable Files
Windows Script
Font Files
Font File
Font Files
Generic Font File
Font Files
OpenType Font
Font Files
TrueType Font
Game Files
Saved Game File
Game Files
Nintendo (NES) ROM File
Game Files
N64 Game ROM File
Game Files
Saved Game
Graphical Interchange Format
Adobe Illustrator File
Graphical Interchange Format
Drawing File
Graphical Interchange Format .dxf
Drawing Exchange Format File
Graphical Interchange Format
Encapsulated PostScript File
Graphical Interchange Format
JPEG Image File
Graphical Interchange Format
JPEG Image File
Graphical Interchange Format
Portable Network Graphic
Graphical Interchange Format
PostScript File
Graphical Interchange Format
Photoshop Document
Graphical Interchange Format
Paint Shop Pro Image File
Graphical Interchange Format
Scalable Vector Graphics File
Graphical Interchange Format
Tagged Image File
Image Files
Multiple Network Graphic
Image Files
Picture File
Misc Files
Windows Installer Package
Misc Files
BitTorrent File
Misc Files
Yahoo! Messenger Data File
Page Layout Files
Adobe InDesign File
Page Layout Files
Portable Document Format File
Page Layout Files
QuarkXpress Document
Page Layout Files
QuarkXpress Project File
Plugin Files
Photoshop Plug-in
Plugin Files
Mac OS X Application Plug-in
Plugin Files
Excel Add-In File
Raster Image Files
Bitmap Image File
Raster Image Files
Graphical Interchange Format File
Settings Files
Configuration File
Settings Files
Windows Initialization File
Settings Files
Registration Information
System Files
Windows Cabinet File
System Files
Windows Control Panel
System Files
Windows Cursor
System Files
Windows Memory Dump
System Files
Device Driver
System Files
Security Key
System Files
File Shortcut
System Files
Windows System File
Text Files
Microsoft Word Document
Text Files
Log File
Text Files
Mail Message
Text Files
Rich Text Format File
Text Files
Plain Text File
Text Files
WordPerfect Document
Text Files
Microsoft Works Word Processor Document
Video Files
3GPP Multimedia File
Video Files
Advanced Systems Format File
Video Files
Microsoft ASF Redirector File
Video Files
Audio Video Interleave File
Video Files
Apple QuickTime Movie
Video Files
MPEG-4 Video File
Video Files
MPEG Video File
Video Files
Apple QuickTime Movie
Video Files
Real Media File
Video Files
Macromedia Flash Movie
Video Files
Windows Media Video File
Web Files
Active Server Page
Web Files
Cascading Style Sheet
Web Files
Hypertext Markup Language File
Web Files
Hypertext Markup Language File
Web Files
JavaScript File
Web Files
Java Server Page
Web Files
Hypertext Preprocessor File
Web Files
Extensible Hypertext Markup Language File
Home » Computer Awareness » Computer – Hardware Parts of the Personal Computer
Computer – Hardware Parts of the Personal
Computer Hardware
Rajesh Goyal
The Major Parts of the Computer : Central Processing Unit (popularly known as CPU) – it consists of different technical
parts like processor, motherboard, hard disc, RAM, CD Drive and cabinet with
 Monitor / Screen
 Keyboard
 Mouse
The major accessories of the computer system ?
. In addition to the above referred major components of the computer, we find the following
accessories attached to most of the computers : Speakers
 Printers
 Scanners
 Modem
 Microphone
Various Hardware Components of A Personal Computer :
PC Case :
It consists of a thin sheet metal enclosure that houses
the motherboard, power supply and various drives (HDD, FDD, CD,
DVD). These cases come in two shapes / styles – desktop and
tower. Now a days the tower type is predominant. It stands upright and is
much taller than it is wide. It is usually placed on the floor near the desk or
under the top of the desk. On the other hand desktop version is pizza box
profile and usually placed on the desktop.
Motherboard :
The motherboard is the main circuit board in a
PC. It contains all the circuits and components that run the PC.
Components found on the motherboard are:
CPU processor.
Full form of CPU is Central Processing Unit or commonly known as
CPU consists of electronic circuits that interpret and execute
instructions. It communicates with the input, output and storage devices. CPU,
with the help of memory, executes instructions in the repetition of machine
It is the brain of every PC. We can say that the CPU is the hardware device
in a computer that executes all of the instructions from the software. All
scheduling, computation and control occurs here.
1. There are two major makers of CPUs namely Intel and AMD. We often hear that CPU
is Intel Pentium or Celeron. Currently the Pentium chip or processor, made by
Intel, is the most common CPU though there are many other companies that
produce processors for personal computers. like CPU made by Motorola and
AMD. The speed of a microprocessor is measured in megahertz, or cycles per
A MHz is a million machine cycles per second. A personal computer of
500 MHz has a processor capable of handling 500 million machine cycles per
second. Another measure of speed is gigahertz (GHz), which means a billion
machine cycles per second.
Full form of BIOS is Basic Input Output System.
It is a non-volatile
memory that contains configuration information about the PC. It contains all the
code required for the CPU to communicate with the keyboard, mouse video display,
disk drives and communications devices.
When a PC is powered on it uses the BIOS „boot code‟ to set up many required functions
that bring the PC to a point where it is ready to work.
Full form is „Real Time Clock‟.
This chip keeps date, day and time in a
24 hour format just like our watch. The PC uses this clock to „time stamp‟ files as
these are created and / or modified.
Chip Set - these are large chip(s) that integrate many functions that
used to be found in separate smaller chips on the motherboard. They save space
and cost.
The functions performed by these chip sets often broken into two devices with one providing
an interface from the CPU to the memory and the other providing controllers for IDE, ISA,
PCI and USB devices (see below).
In addition to above, in a PC, you will notice a number of connectors on the
mother board.
(a)Primary Connectors :
(b)Power -
Some of such primary connectors are :
A 20 pin connector accepts a plug from the power supply.
This plug carry DC power to all the circuits on the motherboard.
©Keyboard - A Mini-din 6-pin (round) connector found at the back of the
motherboard is where the keyboard plugs in.
(d) Mouse - A Mini-din 6-pin connector found next to the keyboard
connector is where the where the mouse plugs in.
(e) Display - This connector is not integrated into the motherboard but is
included in this list since its function is absolutely necessary. It is a 15-pin, D-shell type
connector found on a video card that plugs into the AGP connector of the motherboard (see
(f) IDE - stands for Integrated Drive Electronics. These are 40 pin
connectors that provide a place to connect the ribbon cables from the drives (hard and
CD/DVD). All data between the motherboard and the drives is carried in these cables. They
are not accessible unless the PC cover is removed.
(g) FDD connector -
it is similar in function to the IDE connector.
It is a 34 pin ribbon connector that carries data between the motherboard and any floppy
drive installed in the PC. Not accessible with PC cover on.
(h) DRAM -
Dynamic Random Access Memory connectors for SIMM and
DIMM type memory modules. Not accessible with chassis cover on.
PORTS or Connectors
enable us to connect external output or input
devices to our computer. The basic types of ports are: Parallel ports can be used to connect
printers, zip drives, video capture (such as Snappy), external hard drives, or digital
Serial ports that are frequently used to connect all of the above except
printers. In addition, there are some serial port mice. PS2 ports are used to connect some
types of mice. There are also places on your computer to attach a keyboard and s-video
(A)Serial Connectors
Standard Serial Connector - This connector has been around
in PCs since they first appeared. It was originally located on ISA expansion type cards (see
below). Today it is an integral part of newer motherboards. It is a 9- pin, D-shell connector
that allows you to connect external devices with serial ports to your PC. The maximum data
rate is 115 KB/s.
USB – Universal Serial Bus This is a relatively new serial bus.
Originally specified as low speed, 1.2 Mb/s, it was enhanced to full speed, 12Mb/s. The
latest version 2.0 is specified as high speed, 400 MB/s.
Someday USB will completely replace the standard serial connector that has been the
workhorse serial port in earlier PCs. USB is now a standard connector on all new
Unlike serial and parallel ports, the USB port is designed to power
devices connected to it. The devices must be low power devices and must be able to
reduce their current draw to less than 0.5uAmps when commanded to do so by the PC.
(B)Parallel Connectors
Centronix or Standard Parallel -
This connector has
been around in PCs since they first appeared. It has 37-pins and is now integrated on new
motherboards. It is usually used to connect your printer to the PC and moves data at about
SCSI - Small Computer System Interface moves data at a maximum of up to 80Mb/s. It
not integrated into most PC motherboards. It can be added to a PC as an Expansion card
(see below). Some printers and hard disk drives use SCSI interfaces.
Expansion Card Connectors -
The CPU connects to expansion
card connectors through one of the chip set ICs mentioned above. They are located on the
motherboard near the rear of the PC. These connectors allow special function cards to plug
into and work with the PC.
Before motherboards integrated the serial and centronix connectors they were found on
expansion boards that plugged into ISA slots.
Most PCs have the following expansion connector types:
Industry Standard Architecture connectors have been around since 1980 and
first appeared in the IBM XT PC. This type of slot still appears on some newer motherboards
so that older expansion boards can still be used. However, many motherboards no longer
have ISA connectors on them.
Peripheral Component Interconnect is a newer and faster interface that
accepts all expansion cards that have a PCI interface.
Accelerated Graphics Port is a connector that is designed to work with video
cards. Your video display plugs into and is controlled by one of these video cards. Many
modern video cards offer enhanced 3D-graphics and fast, full motion video.
Power Supply :
A power supply is installed in the back corner of
the PC case, next to the motherboard.
It converts 120 / 240 vac (standard house
power) into DC voltages that are used by other components in the PC. A 20
conductor cable carries +5vdc, -5vdc +12vdc, -12vdc and ground to the
A mouse is an acronym for Manually Oscillating Utensil Sonically
Engaged. It is the electronic finger of the computer. One type of mouse has a round
ball under the bottom of the mouse that rolls and turns two wheels which control
the direction of the pointer on the screen. Another type of mouse uses an optical
system to track the movement of the mouse. Laptop computers use touch pads,
buttons and other devices to control the pointer. Hand helds use a combination of
devices to control the pointer, including touch screens
It is used to point at items in the window environment. The mouse arrow indicates your
position on screen. It can change its shape depending upon your position on screen or the
program you were using. In a word processor the mouse will appear as a flashing
cursor or insertion point. Moving and clicking the mouse can move the cursor onscreen.
The mouse has 2 buttons. The left button is used to send signals to programs. The right
mouse button gives the user various menus. By double clicking the left mouse button,
programs can be opened. A new mouse, the Intellimouse, allows the user to scroll a screen
in a program using a center wheel.
The monitor is the computer‟s screen or display. Monitors come in
sizes from 14 inch, 17 inch, to as large as 36 inch monitor. The resolution of the monitor
determines the sharpness of the screen. The resolution can be adjusted to control the
screen‟s display. The monitor shows information on the screen when you type. This is
called outputting information.
When the computer needs more information it will display a message on the screen, usually
through a dialog box..
Most desktop computers use a monitor with a cathode tube or liquid crystal display.
Most notebooks use a liquid crystal display monitor. To get the full benefit of today‟s
software with full colour graphics and animation, computers need a color monitor with a
display or graphics cards
The keyboard has keys similar to our old typewriter but It
also has some additional keys. The keyboard is used to type information into the computer
or input information.
There are many different keyboard layouts and sizes with the most common for Latin based
languages being the QWERTY layout (named for the first 6 keys).
Function keys are found at the top of the keyboard. These control programs
and are labeled F1 to F12. F1 always provides help in windows environment.
Cursor control keys are arrows that allow you to move the cursor in four
directions (up, down, right, left).
Numeric keys are found on the right side of the keyboard and act much like a
calculator pad, however, “key must be pressed on in order for these keys to function.
ESC or the escape key allows you to exit or escape some programs.
/ Front slash key is used in web addresses on the Internet.
\ Back slash key signals a sub-directory.
Page up and page down keys allow you to move up or down in
a document.
Shift key and caps lock key change the case of the letter when
ALT key moves the cursor to the menu bar, which is useful in the event the mouse
is not functioning.
Pause key pauses text on screen in DOS.
ALT + Ctrl + Delete keys reboots or restarts the computer when they are pushed in that
sequence. This is called a warm boot. A cold boot simply means turning the computer off for
a minute and then turning it back on. These boots are necessary if a program fails to
Backspace key erases errors when the mouse is placed after the error.
Delete key erases errors when the mouse is placed before the error.
7.Printers - The printer takes the information on your screen and transfers it to
paper or a hard copy. There are many different types of printers with various levels of
quality. The three basic types of printer are; dot matrix, inkjet, and laser.
Dot matrix printers work like a typewriter transferring ink from a ribbon to paper
with a series or „matrix‟ of tiny pins.
Ink jet printers work like dot matrix printers but fires a stream of ink from a
cartridge directly onto the paper.
Laser printers use the same technology as a photocopier using heat to transfer toner
onto paper.
Scanners allow you to transfer pictures and photographs to your
computer. A scanner „scans‟ the image from the top to the bottom, one line at a time and
transfers it to the computer as a series of bits or a bitmap.
You can then take that image
and use it in a paint program, send it out as a fax or print it. With optional Optical
Character Recognition (OCR) software you can convert printed documents such as
newspaper articles to text that can be used in your word processor. Most scanners
use TWAIN software that makes the scanner accessible by other software applications.
A Raster Image Processor (RIP) is a component used in a printing system which
produces a raster image also known as a bitmap. The bitmap is then sent to a printing
device for output. The input may be a page description in a high-level page description
language such as PostScript, Portable Document Format, XPS or another bitmap of higher or
lower resolution than the output device. In the latter case, the RIP applies either smoothing
or interpolation algorithms to the input bitmap to generate the output bitmap.
9.Digital cameras allow you to take digital photographs. The images are
stored on a memory chip or disk that can be transferred to your computer. Some cameras
can also capture sound and video.
Computer – Input Devices and Output Devices
Difference between Input Devices and Output
Input devices are those parts of the computer which accept data in a form that can be
utilized by the computer.
Thus input devices help us in feeding the data into the computer
system. Output devices are those parts which show us the data we desired to extract from
the computer. The examples of input / output are :-
A) Input Devices:
A1 : Hand Operated Input Devices
Keyboard and Mouse are the most commonly used hand operated input devices.
Some of the hand operated input devices along with keyboard and mouse are as follow:
Track Ball :
It is used as an alternate of mouse.and has to move its ball
in order to utilize it that causes the pointer to move on the screen.
Joystick : It is very popular among the people fond of computer games, but
today different types of game controllers are replacing them gradually. Joystick is used to
control the machine such as crane in the process of building constructions.
Digital Camera :
Digital camera can take the image and also
records the videos. The images and videos taken by digital cameras are recorded in files.
These files can get copied into the computer that can be further edited for many purposes.
Microphone :
Microphone is used to input the sound. It can be used to
enter text in any word processing application with voice recognition software in the
Touch Screen :
There is a network of light rays in touch sensitive
visual display unit or in screen that recognizes the touch. Touch screen is used in many
mobile phones. They are often used in cash machines and chopping centres.
Video Digital :
Video digital takes the images from video camera or
television and stores it into the computer for further use. The video sequences taken by
video digital are mainly used in multimedia presentation.
Scanner : Scanner is used to convert an image into its digital form. It is
similar to photocopier but it makes digital copy of an image instead of its hard copy. It is
used to scan the text with the software optical character recognition.
Graphic Tablet : There is a flat pad on the graphic tablet upon
which an user writes with the help of a special pen. Pictures can also be drawn on the
screen using that pen in this way.
B) Output Devices :
The means through which computer gives output are known as Output Devices.
of the most popular output devices are as follow:
Sound Card
Video Card
Projector is that hardware device which projects an image on the flat surface like computer
screen. These devices are generally used in meetings, seminars and presentations because
each person can easily see the image projected by it sitting in a big room.
Sound Card
It is also known as Sound Board or Audio Card. Sound card is an expansion card or unified
circuit that enables computer to produce sound through speaker or headphone
It is the device which presents the sound produced during any programme. This is
connected to sound card and gives the sound produced by card in the form of output.
Video Card
It is also known as Graphics Card, Video Board or Video Controller. This is an internal circuit
board that allows the image displaying devices like monitor to display the images.
Integrated Input and Output Devices :
Modem is a connector and is used both as input and output device.
Thus, modem is both
an input device and an output device. Similarly, we can say the latest touch screen display
units also act as input and output devices simultaneously, as we can send instructions to
computer by merely touching the screen and then results are also displayed on the same
MODEM : Full form of modem is MOdulator and DEModulator. The modem is a
converter of analog to digital and digital to analog. Thus, we can say that a modem is a
mechanical means of translating computer information or retrieving information from the
Internet via a phone line. It needs communication software in order to work and can be
attached internally or externally.
Internet transmission can also take place over an
ISDN line or the even faster T1 line. No modem is necessary for these types of transmission
but you will need an ISDN adapter. Modems are measured by the speed that the
information is transferred. The measuring tool is called the baud rate. Originally modems
worked at speeds below 2400 baud but today analog speeds of 56,000 are standard. Cable,
wireless or digital subscriber lines can transfer information much faster with rates of
300,000 baud and up.
The details of the functions performed by each of the hardware are given in the
hardware section.
Computer – Memory in Computers and Disks /
Different Types of Computer Memory
· What is RAM ? The full form of RAM is „Random Access Memory).
as main memory.
Computers can write and read data from RAM.
This is also known
This is in contrast to
ROM which permits you only to read data. However, most RAM is volatile, which means
that it requires a steady flow of electricity to maintain its contents. As soon as the power is
turned off, whatever data was in RAM is lost. The users access data in RAM memory
randomly as per needs. RAM can be erased or written over at will by the computer
What is ROM ?
The full form of ROM is „Read only Memory):
Computers almost
always contain a small amount of read-only memory, commonly known as ROM. This
memory holds instructions for starting up the computer. As name indicates you can only
read from this memory and cannot write anything on it. Moreover, it is non-volatile in
nature i.e. even when power is switched off, the memory is not lost.
Thus, we can say that RAM is like a slate where you can write something for immediate
reference and then wipe / change data by adding or deleting when it is not needed, but
ROM is like a printed book, where once the text is printed then it cannot be altered.
· PROM : The full form of PROM is „Programmable Read-Only Memory‟.
memory chip on which you can store a programme.
A PROM is a
But once the PROM has been used,
you cannot wipe it clean and use it to store something else. Like ROMs, PROMs are nonvolatile.
· EPROM (erasable programmable read-only memory): An EPROM is a special type of
PROM that can be erased by exposing it to ultraviolet light.
· EEPROM (electrically erasable programmable read-only memory): An EEPROM is a
special type of PROM that can be erased by exposing it to an electrical charge.
Memory is measured in bytes. A byte is usually made up of 8 bits and represents one
character – a letter, digit or symbol.
The number of bytes that can be held is a measure of
the memory and storage capacity. Bytes are usually measured in groups of kilobytes,
megabytes, gigabytes and terabytes.
Disk Drives
Secondary memory is also known as external memory or storage. It consists of Hard
Floppy Disc (now a days out of fashion) , CDs and DVDs as well as pen
drives. External device consists of more storage space and most dynamic in terms of
storing data.
The disk drive determines the path by which you send and receive information to the
computer. Information stored on a disk is measured in bytes.
the methods used to represent bytes
We have already explained
1. a : drive and b: drive: The A and B drives on a desktop computers were originally
reserved in the BIOS for floppy disks as at that time floppy drives were very popular and at
one time there used to be floppy drives of different sizes. Floppy disk or diskette used to
comes in two basic sizes; 5.25 inch and 3.5 inch. Both have a low and high density versions
though 3.5 inch high density disks are the most common. The later date diskettes that were
inserted into the a: drive were 3 ½ inch size which could hold 1.44 megabyte of
Initially these disk had to be formatted before being put to use, but later
on pre-formatted disks were available. Formatting prepares the disk to be written upon.
Diskettes can also be write-protected. This prevents you from writing on the disk. To writeprotect a disk, slide the corner tab to uncover the opening. However, now a days most of
the PCs do not have either A or B drives as floppy has become obsolete.
2. c: drive is popularly reserved for the hard disk drive in computers
It is a thick Frisbee-
like disk inside the computer, which can hold considerable highe r information than a
diskette. The hard disk drive reads and stores information faster than the a: drive. The
memory size of these hard disks has greatly enhanced in last few years.
3. d: drive is mostly used for CD-ROM i.e. for playing the CDs . CDs are inserted into this
drive. A CD can contain more information than 100 diskettes. Computers are not able to
write to the CD-ROM drive unless a CD Burner is present. The CD-ROM drives read
information at various speeds. However, sometimes d: drive is a part of the Hard Disk as
such disks are partitioned into more than one segment where c:, d: and even e: are used
for hard disk which has been partitioned.
In addition to above standard features for drives, now a days :
4. Some computers today come equipped with a zip drive. A zip drive provides additional
storage space. A zip disk is inserted into the zip drive. The zip disk can hold 100 megabytes
of information. Zip drives can be attached to an existing computer.
5. DVD (Digital Versatile Disc) drive is a new technology that stores more information than
a CD-ROM and can be written upon. A DVD disk is inserted into this drive. The drive may
come built into the computer or may be attached. These disk often are used to store movies
or interactive video games. The disk resembles a CD but has 7 times the storage capacity.
6. Pen Drives are now popular and may be shown as e: or f: drives.
store data which needs to be carried somewhere else.
Disk size
Amount of storage
These are used to
Approximate printed
8.5 x 11 inch pages
3.5 high density
1.44 Mb
720 pages
650 Mb
a small library
4.5 Gb
a feature length movie
DVD dual layer
8 Gb
a long feature length movie with extras
Methods Used for Reading of Memory :
Sequential access refers to reading or writing data records in sequential order, that is, one
record after the other. To read record 10, for example, you would first need to read records
1 through 9.
This differs from random access, in which you can read and write records in any
Some programming languages and operating systems distinguish between
sequential-access data files and random-access data files, allowing you to choose between
the two types.
Sequential-access files are faster if you always access records in the same
order. Random-access files are faster if you need to read or write records in a random
Devices can also be classified as sequential access or random access. For example, a tape
drive is a sequential-access device because to get to point q on the tape, the drive
needs to pass through points a through p.
The disk drive, on the other hand, is a
random-access device because the drive can access any point on the disk without
passing through all intervening points.
Computer – Software
Software Overview
Software are computer programmes that allow the user to complete a
Broadly speaking the software can be an operating system or an
application which is work specific and works within the environment of the
operating system.
However, sometimes words – software and application – are
interchangeably used.
Software needs to be accessed before it can be used.
There are many terms used for process of accessing software including running,
executing, starting up, opening, and others.
We can classify the software to be Operating Systems, Word processors,
Spreadsheets, Database, Internet Browsers, Emails, Graphic programmes.
All software are stored in files.
some storage devices available.
These files are stored on a disk, card, tape or
There are millions of different pieces of
software available for almost every conceivable need.
Such Software are
available commercially through stores and mail order and also available on the
Internet. Software are also sometimes available through an
Open Source license which allows anyone to use the same free of charge as long
as the license is maintained. If you can‟t find the application that you need,
software development companies can design software as per your specific needs.
An operating system consists of a set of programs, which control, coordinates and
supervises the activities of the various components of a computer system. Its function is to
link between the computer hardware and user. Without an operating system, a computer is
useless. Thus, we can say that operating system software have direct control and
access to the computer hardware and memory locations . They perform I/O
operations on various memory locations , and control the hardware , to make the
application software do a task .
Some examples of Operating systems
/ system software are :
1) Microsoft Windows
2) Linux
3) Unix
4) Mac OSX
5) DOS
6) BIOS Software
7) HD Sector Boot Software
8) Device Driver Software i.e Graphics Driver etc
9) Linker Software
10) Assembler and Compiler Software
It is among the older operating system software and now a days
rarely used as Windows have replaced this once very popular software.
The term
DOS stands for Disk Operating Systemdeveloped by Microsoft for micro computer. It is
the only OS, which can be loaded in the main memory of the computer using a single disk.
It is a single user operating system.
It has a character user interface.
MS DOS provides all the commands for file handling.
Characteristics of DOS
It is not case sensitive.
The file names are restricted to 8 characters only.
It does not support space entries in the file name.
Broad Categories of Operating System
a) Graphic User Interface (GUI) : Itcontains graphics and icons that can be regulated by
mouse. Some of the GUI operating systems are as follows:
System 7.X ;
Windows 98 ;
Windows CE
b) Multi-user : With the help of multi-user operating system, a computer can be used by
more than one user at the same time or in different time intervals. Some of the examples of
multi-user operating system are as follows:
Linux ; Unix ; Windows 2000
c) Multi-processing : Multi-processing operating system is capable of getting the work
done from the computer by extending support to more than one processors. Some of the
examples of multi-processing operating system are as follows:
Linux; Unix ; Windows 2000
d) Multi-tasking : With the help of such operating system, a number of softwares can be
executed at one time. Some of the examples are as follows:
Unix ; Windows 2000
e) Multi-threading : With the help of such operating system, different parts of a software
program can be executed simultaneously. Some of the examples are as follows:
Linux ; Unix; Windows 2000
Application Software
Application software run under System Software , and are made to do a specific
task. These software are popularly called as application softwares.
examples such applications are :
Some good
Web browser (Internet Explorer, Chrome, Opera, Safari, Mozilla, Netscape, Firefox) –
Used for viewing pages on World Wide Web;
Word processing software, ( MS Word, Corel WordPerfect, Abiword) – used for
writing letters, reports, essays, novels and other types of text
Spreadsheet software (MS Excel, Lotus 123, VisiCalc ) – Track budgets, balance
sheets, investments
Database software (MySQL, Access, Oracle, Sybase, 4 th Dimension)
Photo Editors (Photoshop, Fireworks, PhotoPaint, Gimp)
Presentation graphics software (MS Powerpoint) – create slideshows for meetings
Music / Sound Software (iTunes)
Audio / Video Software (VLC Medica Player)
Graphic Software (Adobe Photoshop)
Email clients (Outlook, Eudora, Entourage) – Used for sending emails and files to
other people
Desktop Publishing (PageMaker, InDesign, QuarkXPress) – used for making a
magazine a poster or an advertisement;
Computer-aided Design software (AutoCAD, SolidWorks, MicroStation) – used to
create blueprints or designs;
We have already clarified that all computers need some sort of Operating System
(OS) so as to access and control the hardware.
Now a days, on most of the PCs
we use some form of Microsoft‟s operating systems. The original Microsoft
operating system was called DOS (Disk Operating System), but the same has now
become obsolete.
Now most computers use Windows. Windows comes in various
versions beginning with version 3.x then 95, 98, ME, XP, Vista and currently
version 7 and Version 8.1. In some computers, people use IBM‟s O/S2. Apple‟s
Mac use their own operating system beginning with OS 1 though to OS 10.x.
Some computer professionals, Internet Service Providers (ISP) and mainframe
computer users use an operating system such as UNIX (or a variant such as
Linux), Windows NT or 2000 (Win2k) or one of the other network or server based
operating systems.
Computer – Microsoft WORD
MicroSoft Word
Microsoft Word is a word processor designed by Microsoft. It was first released in
1983 under the name Multi-Tool Word for Xenix.
A word processor can be used to manipulate text data to produce a letter, a report,
a memo, an e-mail message, or any other type of correspondence. Text data is any
letter, number, or symbol that you can type
on a keyboard.
The grouping of the
text data to form words, sentences, paragraphs, and pages of text results in the
creation of a document. Thus, we can say that a word processor is a program
used to type documents. Such Documents can be saved, closed and the opened
again to continue working on them.
It was not initially popular, since its user interface was different from the leading word
processor at the time, WordStar.
1987, was named Word 3.0
The second release of Word for Macintosh, shipped in
In 1993 Word for Windows 6.0 version was
released. Thereafter, we had Word 95, Word 97, Word 98, Word 2000, Word 2002, Office
Word 2003, Office Word 2007, were released. In 2010, was released Word 2010 and now
in 2013, Word 2013 which is also part of Office 2013 has been released.
The purpose of this tutorial is not to teach as to how to operate Word software,
but to give you idea to some of the commands and procedures followed in day to
day use of the application.
The material given here has been compiled keeping
in view the questions asked in the competition exams.
What is MS Word used for?
MS Word is used for creating documents such as letters, brochures, learning activities,
tests, quizzes and students‟ homework assignments. There are many powerful features
available in Microsoft Word to make it easier to learn for students with disabilities.
The components of a word window are as
a)Title Bar : It shows the name of the file on which you are working. It also consists of
three buttons as Minimize button reducing the window to an icon, Restore button bringing
word window to the maximum original size and close button bringing us out of word.
b) Menu Bar: It consists of various commands.
c) Standard Tool Bar : It displays the symbols for the common operation like open, print,
save, etc.
d) Formatting Tool Bar: It displays the options which can be used to format our document
like font type. Size of the font, bold, underlines, bullets, alignment, etc.
e) Ruler : It shows the width of the document which can be increased or decreased.
f) Workspace :It is the area, where the text can be entered.
g) Vertical Scroll Bar : It is used to see the text at various positions.
h) Horizontal Scroll Bar : It is used to move from left side to right side in the document
and vice-versa.
i) Drawing Tool Bar :This is used for making drawings in the document.
j) Status Bar :This Bar will always show you your current position as for the text goes.
What is a Cursor :
In computers, a cursor is an indicator used to show the
position on a computer monitor or other display device that will respond to input from a text
input or pointing device. The flashing text cursor may be referred to as a caret in some
cases such as in caret browsing. The mouse cursor may be referred to as a pointer, owing
to its arrow shape on some systems.
What is an insertion Point :
An insertion point is the location on the screen where
the next character typed will be inserted. This location may be in a text document, a form
field, a Web browser address bar, or anywhere else on the screen that allows text
input. The insertion point is often identified by a flashing cursor. This cursor is called an “Ibeam pointer” and is shaped like a capital “I” or a long vertical line. When you type a
character on the keyboard, it will appear on the screen directly to the right of the flashing
cursor. The insertion point continues to move to the right as each character is entered.
In word, we can insert the text anywhere by clicking the mouse at the relevant
point. On clicking the mouse button, blinking insertion point of I shape will
appear on the screen the insertion point. Now if any text is typed, it will appear
just to the left of the insertion point / cursor. The text appears at the cursor.
Use space bar to create space between two characters;
Use backspace to erase to the left of the cursor; and
Use delete to erase to the right of the cursor.
Use Enter (or Return) to move the cursor down a line.
Word processors allows you to type your text in Bold, Italics or Underline. To
activate Bold, Italics or Underline click the icon button on the Toolbar, type the
text that you wish to have highlighted then press Toolbar icon again when you are
finished. The indicator on the Toolbar will appear highlighted as long as the
highlight style is on.
There are large number of short-cuts available for various commands in MS
Word. We give below some of the major short cuts that are available:
Common tasks in Microsoft Word
To do this
Make letters bold.
Make letters italic.
Make letters underline.
Decrease font size one value.
Increase font size one value.
Decrease font size 1 point.
Increase font size 1 point.
Remove paragraph or character formatting.
Copy the selected text or object.
Cut the selected text or object.
Paste text or an object.
Paste special.
Paste formatting only
Undo the last action.
Redo the last action.
Open the Word Count dialog box.
Working with documents and webpages Create, view and save documents
To do this
Create a new document.
Open a document.
Close a document.
Split the document window.
Remove the document window split.
Save a document.
Find, replace and browse through text
To do this
Open the Navigation task pane (to search
Repeat find (after closing Find and
Replace window).
Replace text, specific formatting, and special
Go to a page, bookmark, footnote, table,
comment, graphic, or other location.
Switch between the last four locations that you
have edited.
Open a list of browse options. Press the arrow
keys to select an option, and then press ENTER
to browse through a document by using the
selected option.
Move to the previous browse object (set in
browse options).
Move to the next browse object (set in browse
Edit and move text and graphics
Delete text and graphics
To do this
Delete one character to the left.
Delete one word to the left.
Delete one character to the right.
Delete one word to the right.
Cut selected text to the Office Clipboard.
Undo the last action.
Cut to the Spike.
Computer – Microsoft Excel Overview
Microsoft Excel
MS Excel stands for MicroSoft‟s spreadsheet programme that is used for storing, organizing
and manipulating data. This software is a powerful computer programme is a part of the
MS Office and is available for operating system of Microsoft Windows and Mac OS X. This is
the most used spreadsheet programme these days. We give below a screen shot of Excel
Screen with some inputs about how it can be useful for calculation of salary of employees in
an organisation. It has the ability to perform complex operations, save time and improve
Microsoft Excel is a spreadsheet application.
It is a part of MS Office.
It features calculation, graphic tools, pivot
tables and a macro-programming language called
Visual Basic For Applications (VBA).
A look at the above Excel screen shows that “spreadsheet” is a rectangular table with grids
of rows and columns. The horizontal rows are identified by numbers (1,2,3,4,5….) and the
vertical columns with letters of alphabet (A,B,C,D,E….).
MS Excel popularly known as “Excel” is a very powerful software with so many features that
it is not possible to discuss even a fraction of these in these pages. The features include
calculation, graphing tools, pivot tables and a macro programming language called Visual
Basic for Applications.
What is a Cell in Excel ?
The intersection point (i.e. the small rectangular box) between a column and a row is called
a Cell. This “cell” is the basic unit for storing data in the spreadsheet. There can be
thousands of cells in a spreadsheet depending on the amount of data you are storing. To
identify or refer to data stored in a particular cell, it is identified by so called “cell
reference”. For example, in the above screen shot, 5000 is in cell referred as B4. Thus,
we can say that cell reference is a combination of the column letter and the row number.
Can You Give Me Some of the Uses of MS
Excel :
Excel is used for a large number of functions. Some of the functions for which Excel is
widely used includes, (a) Managing data records like name list (you are easily sort
alphabetically); (b) Analysis through pivot tables; (c) corporate budgeting; (d) creating
forms and consolidating results; (e) inventory management ; (f) Breakeven analysis.
Some important terms relating to MS Excel :
a) Worksheet : It is a grid of cells made up of horizontal rows and vertical columns. It
contains 65536 rows and 256 columns.
b) Row Number : Each row is given a number 1,2,3,4, …. So on.
c) Column Letter : Each column is given a letter starting from A…Z, AA….ZZ,
BA…BZ, ….IA – IV.
d) Cell : It is basic unit of worksheet where numbers, text, formulae, etc, can be place.
e) Cell Pointer : It is a cell boundary that specifies which cell is active at that moment.
f) Current Cell : It is a cell which is active.
g) Range of Cell : It is a group of contiguous cells that forms a rectangular are in shape.
h) Work Book : A worksheet is a grid of cells made up of rows and columns. Multiple
worksheets can be combined under a file known as Work Book.
i) Data in Worksheet : Three types of data can be entered, numbers/characters,
text and formulae.
j) Formula : It is a sequence of values, cell address, names functions or operators in a cell
that produces a new value from existing values.
k) Cell Referencing : Each cell in worksheet has a unique address, when cell address is
referred in formulas, it is called Cell Referencing.
l) Relative Referencing : Cell referencing in which the cells are referred by their relative
position in the worksheet relative to a particular cell.
m)Absolute Referencing : Cell referencing in which the cells are referred by their fixed
position in the worksheet.
n)Mixed Referencing : Combination of relative and absolute referencing is called Mixed
o)Functions : Functions are predefined formulae that perform calculations by using specific
values called arguments.
p) Structure : The structure of a function begins with the function name, followed by an
opening parenthesis, the arguments for the function separated by commas and a closing
q) Charts : Charts are the pictorial representation of worksheet data.
r) Area Chart : An area chart emphasizes the magnitude of change over time.
s) Column Chart : A column chart shows data changes over a period of time.
t) Bar Chart : It illustrates comparisons among individual items.
u) Line Chart : It shows trends in data at equal intervals.
Excel Keyboard Shortcuts
The following keyboard short cuts can be used to increase the speed and smooth
functioning in the MS Excel spreadsheet work.:
Hide / Unhide shortcuts:
Hide the selected row(s)
Unhide any hidden row(s) within selection
Hide the selected column(s)
Unhide any hidden column(s) within selection
Navigation shortcuts:
Move to the beginning of the Row
Move to the beginning of the Worksheet
Move to the bottom-most and right-most used cell in the
Move to the Next Sheet in the workbook
Move to the Pervious Sheet in the workbook
Move one screen to the Right
Move one screen to the Left
Selection shortcuts:
Select the current sheet and next sheet
Select the current sheet and previous sheet
Select the entire COLUMN
Select the entire ROW
Select current range
CTRL+SHIFT+O(letter O)
Select cells that contain Comments
Select the current region around the active cell
Select the array containing the active cell
Select all cells that contain formulae that directly reference
active cell
Select all cells that contain formulae that directly or
indirectly reference active cell
Date & Time related shortcuts:
Insert current date
Insert current time
Number Formatting shortcuts:
General Format the numbers in selected range
Apply Percentage format to numbers in selected range
Apply Currency format to numbers in selected range
Apply date format (dd/mm/yy) to the selected cell(s)
Apply Exponential number format with 2 decimal places to
the selection
Apply Number format with 2 decimal places, thousands
separator and minus sign for -ve numbers
General Cell / Range Formatting shortcuts:
Format cells menu
Apply outline border to the selection
CTRL+SHIFT+ _ (underscore)
Remove the outline border to the selection
Apply (or remove) Strikethrough format to the selection
Apply (or remove) Bold format
Apply (or remove) Italic format
Apply (or remove) Underline format
Copy data shortcuts:
Fill Down
Fill Right
CTRL+, (comma)
Copy formula from cell above to the active cell
CTRL+” (double quotes)
Copy value from cell above to the active cell
Other shortcuts:
Insert hyperlink menu
Toggle formula view
Repeat last action
Chart selected data
Computer – Microsoft PowerPoint
Microsoft Power Point Software
Powerpoint is the presentation graphics part of MS Office suite.
Powerpoint can create various presentation materials like charts, graphics, slides,
handouts, overheads, etc.
Powerpoint even creates slide shows.
Auto Content Wizard, Design Templates, Sample Presentation and Blank Presentation
are the methods for creating new presentation.
Presentation can be saved and run in any of the file formats: the 2003 default .ppt
Pps (powerpoint show) or .pot (template).
Custom animation can be used to create small story boards by animating pictures to
enter, exit or move.
Powerpoint presentation can be made up of a number of pages or slides.
Computer – Microsoft Access
Microsoft Access Software
Microsoft Access is a relational database management system that combines the
relational Microsoft Jet Database Engine with a graphical user interface and software
development tools.
It stores data in its own format based on the Access Jet Databases.
It can also import or link directly to data stored in other Access databases.
A database is a collection of data of a particular type.
Data in a database is stored in the form of tables.
A table is a row and column arrangement of information.
A table is also called a Relation.
The table contains data organized under specific categories.
Each such category is arranged vertically in a table and is called a Column.
Every column in a table has a unique name.
A column can also be referred to as a field.
Data organized horizontally is termed as a row.
Relational Database Management System (RDBMS) is a multi-table database where
the tables in the database have to be related for storing or retrieving data.
Microsoft Access is an RDBMS that enable to manage relational database in a
windows environment.
MS Access enable you to enter, retrieve and modify data and also create forms and
Database Objects
a) Table :
They store data in a row and column format similar to spreadsheets.
b) Queries : They enable you to view data from a table.
c) Forms : They enable you to enter, view and modify in a table.
d) Reports :
They enable you to generate reports based on tables and query
e) Data Access Page : They are web pages to view data from the
internet where the data is stored in an Access database.
f) Macros : They are a series of commands and functions that can be executed
whenever a task is needed to perform.
g) Modules :
They are a set visual basic procedures and declarations stored as
one unit.
Computer – What happens when we switch on
the computer
What Happens When We Switch On Computer
When we put power on in our computer, it first of all loads the operating
system. This procedure popularly is known as „booting‟ up of computer.
Thus, we
can say that the computer starts from scratch every time we turn the power
It checks all its components. In case there is any problem with any
component, it will usually display a message. Loading the operating system is
usually automatic.
On most PCs these days, Microsoft Windows is used. However, Mac OS or Linux as their
operating system are also used by some users.
All these Operating Systems (OS) are
Graphic User Interface (GUI) systems and thus allows the user to control or run the
computer using a Mouse and clicking on the icons. The user simply moves the mouse on a
flat surface, rolls the trackball, or moves their hand over the touch pad to control a pointer.
They then choose the option they want by pressing a button or touching the pad.
Without a GUI the user controls the computer using the keys on the keyboard. This is
referred to as a Command Line Interface (CLI) which was popular under DOS environment.
Once the system is loaded the user can start the application or program that they are going
to use.
A typical computer process includes
(a) inputting the information;
(b) Processing the information;
(c) Outputting the information.
The information is inputted through input devices like keyboards, mouse, disks, scanners
and other devices.
The information is processed in CPU and the processed information
displayed either on Monitor (soft copy), stored on the disk, or taken as a hard copy through
a printer.
Computer – Data Communication and Network
Some Basic Facts
Signals are electric or electromagnetic encoding of data and signaling is propagation
of signal along suitable communication medium.
Transmission is communication of data achieved by the propagation and processing of
In parallel data transmission, each wire carries a bit of information.
In series data transmission, each bet is sent sequentially one after another and it is
slower than that of parallel transmission.
In synchronous transmission, characters are transmitted as groups, with control
characters in the beginning and at the end of the bit train.
In a synchronous transmission, each character is transmitted separately.
In simplex mode of communication, channel is used in one direction.
In half duplex mode of communication, channel is used in both directions.
In full duplex mode, the communication channel is used both directions at the same
Computers are connected with each other for communication creating the
computer network. Computer network is of three types:
1. Local Area Network (LAN)
2. Metropolitan Area Network (MAN)
3. Wide Area Network (WAN)
Local Area Network (LAN) It is a data communication network, which connects many
computers of workstations and permits exchange of data and information among
themselves, within a localized area.
Metropolitan Area Network (MAN) It is a network of computers of a large region. For
example, all the branched of an electric department of a city and the network of computers
of all the offices.
Wide Area Network (WAN) It is a network linking separate geographical locations.
Internet is the best example of it.
Computer – Topology
Topologies Used in Computer
A network topology is the physical layout of the network in which all the
devices are connected among themselves. The point of connection to the network
by the stations are called Computer Nodes or Link Stations.
When a number of stations are connected directly to the central station or
controller it is known as Star Topology.
When all the stations are connected to a single communication line that is
referred to as a bus, it is known as Bus Topology.
When all the stations are connected with each other in a logically circular form, it is
known as Ring Topology. Failure of a station in a ring topology causes the disruption in the
entire ring framework.
Computer – Uniform Resource Locator
Each Internet service employs a particular protocol. This specific protocol defines
the rules of engagement for computers conveying the information on that
particular service. This protocol is shown at the beginning of the Uniform
Resource Locator (URL) for each site. For example, the URL for a website is
frequently in the form of, indicating that this is an HTTP
URLs are sometimes known as a Uniform Resource Identifier (URI), or popularly in
short as an „address.‟.
URLs can contain both uppercase and lowercase letters, although it doesn‟t usually matter
which case is used for any of the letters. In all instances, however, they can only contain
standard ASCII characters, corresponding to those that you can actually see on your
computer keyboard. Note that spaces or other control codes are not permitted.
Suffixes and Top-Level Domains :
Most of the time we use
.com at the end (i.e. suffix) of the domain
However, some of other common URL suffixes, are:-
Kind of Site
Academic body
Business organisation
Commercial business (not USA)
Commercial business (USA or
Co-operative organisation
Educational establishment
Civilian government
Information site
Military government
Named individual
Network gateway
Non-commercial organisation
Professional body
With the internet become bigger and bigger, some other countries have started new
suffixes, which identify the region. An extra code is often required to identify the region,
which is commonly known as the top level domain (TLD). Here are a few examples:-
European Union
Ex-Soviet Union state
United Kingdom
USA (Other sites)
Computer – Important Terms Used in Internet
Internet – Overview and Terms Used
An Internet is a global connection of computers linked together by cables and telephones
and makes the communication possible among them.
We can also say that an internet is
a ” computer network consisting of a worldwide network of computer networks that use the
TCP/IP network protocols to facilitate data transmission and exchange”.
some of the basic rules used for transferring the data across internet.
The following are
For such communication, the address of the destination and a safe means of moving
data are required.
The rules governing the sending and receiving of data on the Internet are
implemented in two parts asTransmission Control Protocol (TCP) and Internet
Protocol (IP).
Transmission Control Protocol divides the data into little data packets.
The rule of Internet Protocol here is put destination addressing information on such
Hosts are in general, individual machines at a particular location.
Domains are general category that a computer on the internet belongs to.
E-mail is mainly used for sending electronic piece of text.
Use net and news groups are set up by people sharing common interests ranging
from current topics to cultural heritages.
Telnet is a program that allows and Internet host computer to became a terminal of
another host on the Internet.
Gopher displays a set of resources on the Internet in the form of menus or lists of
Users of Internet and Some Basics :
At present internet contains billions of web pages which have been created by people and
companies across the world.
Thus, it has almost limitless location and is used to access
information and entertainment. The Internet also has thousands of services that help make
life more convenient. For example, banks offer online banking that enables a user to
manage and view their account online. Similarly, youth can apply for jobs online.
The Internet is explored, which is more commonly referred to as surfing, using a
computer browser.
Finding information on the Internet is achieved by using a search engine e.g. Google
Users browse web pages by following hyperlinks.
Files, pictures, songs, and video can be shared by uploading and downloading.
The Internet is also used for communicating with others through social networks,
forums, chat, e-mails, and IM, for example Facebook, Skype
Some Common Terms Used in Internet
Hypertext Markup Language (HTML) is a language to create documents for words
wide web.
Standard Generalised Markup Language ( SGML) is used to define the structure
and mange the content of a digital document.
World Wide Web (WWW) is a giant collection of hypertext pages on the Internet.
Hyper Text Transfer Protocol (HTTP) is used to manage all the linkings between
one hypertext document and another.
On the Internet, a home page may be related to a single person a specific subject, or
to a corporation.
Uniform Resource Locator(FTP) is a way to avail of Internet resources.
File Transfer Protocol(FTP) is used to access a remote Internet host.
Modem is a device allowing a computer to transmit information over a telephone
line. It acts as a modulator and demodulator while the process of transmitting and
Wide Area Information Service (WAIS) is a type of service to access text
databases or libraries on the Internet.
Mosaic gives access to Internet resources by using graphical user interface allowing
users to navigate through hypertext documents.
Archie is used to locate files available by anonymous FTP, it is also known as Global
Home » Computer Awareness » Computer – CAPTCHA
Computer – CAPTCHA
What is CAPTCHA ?
A CAPTCHA is a program that can generate and grade tests that humans can pass
but current computer programs cannot. For example, humans can read distorted
text (as the one given below), but current computer programs can‟t
What is full form of CAPTCHA :
The full form of CAPTCHA is “Completely Automated Public Turing test to tell
Computers and Humans Apart”. This is a trademark of Carnegie Mellon
University, and can be termed as a type of challenge-response test used in
computing to determine whether or not the user is human. The term was coined in
2000 by Luis von Ahn, Manuel Blum, Nicholas J. Hopper of Carnegie Mellon
University, and John Langford of IBM.
The most common type of CAPTCHA was first invented by Mark D. Lillibridge,
Martin Abadi, Krishna Bharat, and Andrei Z. Broder. This form of CAPTCHA requires
that the user type the letters of a distorted image, sometimes with the addition of
an obscured sequence of letters or digits that appears on the screen. Because the
test is administered by a computer, in contrast to the standard Turing test that is
administered by a human, a CAPTCHA is sometimes described as a reverse Turing
test. This term is ambiguous because it could also mean a Turing test in which the
participants are both attempting to prove they are the computer.
What are the uses of CAPTCHA ?
CAPTCHAs have several applications for practical security. Some of the important
uses of CAPTCHA are as follows:•
It Prevents Comment Spam in Blogs – We have heard that in some cases
bogus comments are submitted either as a spam or to to raise search engine ranks
of some website.
Usually, such spam comments are generated through computer
programmes. Thus, by using a CAPTCHA websites can eliminate such spam
comments as in that case only humans can enter comments on a blog.
To Prevent Fake Registration – There are many companies which offer
free email services. Till few years back, most of such services experienced bots
attack that would sign up for thousands of email accounts every minute.
problem was resolved by introduction of CAPTCHA before final submission of the
details as it ensured that only humans obtain free accounts.
In general, free
services should be protected with a CAPTCHA in order to prevent abuse by
automated programs.
Online Polls important role.
In order to prevent fake polling votes , CAPTCHA plays an
Preventing Dictionary Attacks.
dictionary attacks in password systems.
CAPTCHAs can also be used to prevent
The idea is simple: prevent a computer
from being able to iterate through the entire space of passwords by requiring it to
solve a CAPTCHA after a certain number of unsuccessful logins.
Worms and Spam. CAPTCHAs also offer a plausible solution against email
worms and spam: “I will only accept an email if I know there is a human behind
the other computer.” A few companies are already marketing this idea
A virus is a program or code that replicates itself onto other files with which it comes in contact; that
is, a virus can infect another program, boot sector, partition sector, or a document that supports
macros, by inserting itself or attaching itself to that medium. Most viruses only replicate, though many
can do damage to a computer system or a user‟s data as well.
A worm is a program that makes and facilitates the distribution of copies of itself; for example, from
one disk drive to another, or by copying itself using email or another transport mechanism. The worm
may do damage and compromise the security of the computer. It may arrive via exploitation of a
system vulnerability or by clicking on an infected e-mail.
A Trojan Horse portrays itself as something other than what it is at the point of execution. While it
may advertise its activity after launching, this information is not apparent to the user beforehand. A
Trojan Horse neither replicates nor copies itself, but causes damage or compromises the security of
the computer. A Trojan Horse must be sent by someone or carried by another program and may
arrive in the form of a joke program or software of some sort. The malicious functionality of a Trojan
Horse may be anything undesirable for a computer user, including data destruction or compromising a
system by providing a means for another computer to gain access, thus bypassing normal access
Computer Virus
A computer virus is a computer program that can copy itself and infect a computer. A virus can spread
from one computer to another when its host is taken to the target computer, for instance because a
user sent it over a network of the Internet, or carried it on a removable medium such as a floppy disk,
CD, DVD or USB drive. Viruses can increase their chances of spreading to other computers by infecting
files on a network file system or a file system that is accessed by another computer.
Important Facts Related to Computer Virus
The Creeper virus was first detected on ARPANET, the forerunner of the Internet, in the early
The Reaper Program was created to delete creeper.
The actual term „virus‟ was first used in David Gerrold‟s 1972 novel, when HARLIE was one.
A program called “Elk Cloner” was the first computer virus to appear “in the wild” this is, outside
the single computer or lab where it was created
It attached itself to the APPLE DOS 3.3 operating system and spread via floppy disk.
The first PC virus in the wild a boot sector virus “Brains” created in 1986.
With the spread of personal computer, traditional computer viruses emerged in 1980. Bulletin
board-driven software sharing contributed directly to the spread of Trojan horse programs. Shareware
and boot leg software were equally common vectors for viruses on BBS.
Macro Viruses have become common since the3 mind 1990.ost of these viruses are written in
the scripting languages for Microsoft Programs such as word and Excel and spread throughout
Microsoft Office by infecting documents and spreadsheets.
Viruses that spread using cross site scripting were first reported in 2002 and were academically
demonstrated in 2005. There have been multiple instances of the cross site scripting viruses in the
wild, exploiting websites such as My space and Yahoo.
The most popular five computer virus came into light as far as follows :
I Love You (2000) It spreads through e-mails.
Code Red (2001) It affects window server.
Nimada (2001) It is the most rampant virus.
Melissa (1999) It spreads through World Macro and e-mails.
Sasser (2004) It spread by attaching to port 445 on the network windows system.
Antivirus Software and Other Preventive Measures
Antivirus software can destroy the viruses by finding them. The antivirus software uses two common
methods in order to detect viruses.
Using the Virus Signature Definitions list.
By using Heuristics Algorithm
Some antivirus programs are capable of „On the Fly‟ scanning of received e-mails along with scanning
of the open files. This process is known as „On-Access‟ scanning.
Antivirus software does not alter the efficiency of the host software for the communication of viruses.
These software need to be updated regularly so that the new viruses can be detected.
The loss incurred by the viruses can also be negated by the regular backup of data on other mediums.
If any data get misplaced due to this virus then we can retrack it by backup.
Five new Computer Antivirus Software are as follows:
Kaspersky Antivirus 2010
Symantec Norton Antivirus 2010
McAfee Antivirus Plus 2010
Panda Security Antivirus Pro 2010
Trend Micro Antivirus + Anit Spyware 2010
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