01 Architecture of Computer

 The word computer has been derived from the Latin word 'Computare', which means
to compute or to calculate.
 A computer can be defined as an electronic device used to calculate and manipulate
the data (i.e. input) and generates an output in the form of useful information by
following a set of procedural instructions.
 British scientist Charles Babbage is considered as the Father of Computer.
 He invented the first mechanical computer in early 19th century and further in 1833,
he conceived a automatic analytical engine for performing arithmetic functions.
 Alan Mathison Turing is widely regarded as the Father of Modern Computers or
Father of theoretical computer science and Artificial Intelligence (AI).

Computer Architecture

Computer architecture deals with the functional behaviour of a computer system as viewed
by a programmer.
 It can also be described as the logical structure of the system unit that housed
electronic components.
 The computer architecture forms the backbone for building successful computer
systems. The first computer architecture was introduced in 1970.

Components of Computer

A computer consists of following three main components:

1. Input/Output Unit
2. Central Processing Unit
3. Memory Unit

Input Unit
 The computer accepts coded information through input unit by the user.
 It is a device that is used to give required information to the computer. e.g.
 Keyboard, mouse, etc.

Output Unit
 Output unit sends the processed results to the user.
 It is mainly used to display the desired result to the user as per input instructions. e.g.
Monitor, printer, plotter, etc.

Central Processing Unit (CPU)

 It consists a set of registers, arithmetic logic unit and control unit, which together
interpret and execute instructions in assembly language.
 Central Processing Unit is often called the brain of computer.
 The CPU is fabricated as a single Integrated Circuit (IC) and is also known as
microprocessor.
 A CPU controls all the internal and external devices and performs arithmetic and
logic operations.

The primary functions of the CPU are as follows:

1. The CPU transfers instructions and input data from main memory to registers, i.e. internal
memory.
2. The CPU executes the instructions in the stored sequence.
3. When necessary, CPU transfers output data from registers to main memory.

The CPU consists of following main sub-systems:

Arithmetic Logic Unit (ALU)

 ALU contains the electronic circuitry that executes all arithmetic and logical
operations on the available data.
 ALU uses registers to hold the data that is being processed.

Most ALUs can perform the following operations:

1. Logical operations (AND, NOT, & OR)

2. Arithmetic operations (addition, subtraction, multiplication and division).
3. Bit-shifting operations (shifting or rotating a word by a specified number of bit to the left
or right with or without sign extension).
 4. Comparison operations (=, ≠, <, ≤, >, ≥)

Control Unit (CU)

 CU coordinates with the input and output devices of a computer.
 It directs the computer to carry out stored program instructions by communicating
with the ALU and the registers.
 It organises the processing of data and instructions.
 The basic function of control unit is to fetch the instructions stored in the main
memory, identify the operations and the devices involved in it and accordingly
generate control signals.

Memory Unit
 This unit is responsible to store programs or data on a temporary or permanent basis.

 It has primary memory (main memory) and secondary memory (auxiliary memory).
 The input data which is to be processed is brought into main memory before processing.
 Another kind of memory is referred to as secondary memory of a computer system. This
unit is used to permanently store data, programs and output.
 This unit does not deal directly with CPU.

02 Input and Output Devices

 Computer hardware refers to the physical components of a computer that can be seen
and touched by the user.
 Hardware is one of the basic and necessary parts of a computer system.

Input Devices
 An input device is a hardware device that sends data into the computer system.
 These devices are used to input (or enter) data and instructions into the computer
system.
 All instructions are accepted by the CPU through electrical pulses from various kinds
of input devices.
Some of the input devices are explained as follows:

Keyboard
 It is the most commonly used input device which uses an arrangement of buttons and
keys.
 Both data and program, can be entered into the computer using the keyboard.
 It is an essential device for interactive processing because the user can easily issue
commands to receive the data response immediately on the computer screen.

Mouse
 Mouse is a pointing device that allows to control the movement of pointer (also
known as mouse pointer) on screen.
 Mouse performs various functions by detecting two-dimensional motion relatively to
its supporting surface.
 A mouse can be of different types like wired, wireless mouse, optical mouse,
mechanical mouse etc.
 Generally a mouse have two buttons - a right button and left button.

Joystick
 The joystick is also a pointing device like the mouse, which consists of a stick that
pivots on a spherical ball on its base.
 A joystick is similar to a mouse excepts that the moment of cursor on screen stops
working as soon as user stop moving the mouse.
 But with a joystick, the pointer continuous moving in the previously pointing
direction.

Light Pen
 A light pen is a pointing device shaped like a pen and is connected to a Visual
Display Unit (VDU).
 The tip of the light pen contains a light-sensitive element which, when placed against
the screen, detects the light from the screen.
 It enables the computer to identify the location of the tip of pen on screen.

Graphics Tablet
 A graphics tablet (or digitisers, digitising tablet, tough tablets or simply tablet) is an
 input device that consists of an electronic writing area and a special pen that works
with it.
 It allows artists to create hand-made images and graphical images with motion and
action, similar to the way a person draws images with pencil and paper.

Touch Screen
 It is an electronic visual display that can detect the presence and location of a touch
within the display area.
 The touch screen sends a signal to the computer. This signal gives the location on the
screen, which has been "touched".
 Touch screen is quick and simple to use. Generally, smartphones have a high-
resolution capacitive touch screen.

Scanner
 It is a device that allows a user to take an image or text and convert it into a digital
file, allowing the computer to read or display the scanned object.
 Scanners can be used for storing the documents in their original form that can be
modified and manipulated later.
 It is mainly used to convert a scanned document in a digital format.

Barcode Reader
 It is an input device used for reading printed bar codes (Universal Product Code)
available on product to be sold.
 A barcode reader emits a beam of light, which reflects off the barcode image.

Output Devices

An output device is a part of computer hardware equipment, used to communicate the results of
data processing which are carried out by an information processing system (such as a computer),
to the outside world.
Output devices carry the results of various operations performed by the user.

Some of the devices, which are used to display the processed result or output are as follows:
Monitor
 A monitor (called a visual display unit) is an electronic visual device used to display
the output.
 The rectangular area of the monitor, its refresh rate and dot pitch, all directly affect
the resolution of the display.

Various types of monitor are:

1. LCD (Liquid Crystal Display)


A special type of liquid is sandwiched between two plates.

It is a thin, flat and lightweight screen made up of any number of color or
monochrome picture pixels arranged in front of a light source.
2. LED (Liquid/Light Emitted Diode)


It is an electronic device that emits light when electrical current is passed
through it.
3. TFT (Thin Film Transistor)


A LCD with active-matrix displays, each pixel is controlled by one to four
transistors that can make the screen faster, brighter, more colorful than
passive-matrix and capable of being viewed at different angles.
4. 3-D Monitors

 These describe an image that provides the perception of length.

 When 3-D images are made interactive then user feel involved with the scene,
and this experience is called virtual reality.

Printer

 A printer is an output device, which produces a hard copy of documents that are
stored in an electronic form on physical print media such as paper or transparencies.
 So, Printers are the primary output devices used to prepare permanent documents.
 The speed of a printer is normally rated either by Pages Per Minute (PPM) or by
Characters Per Second (CPS).
Printers can be classified into two broad categories:

1. Impact Printer

 Dot matrix, daisy wheel, line printer, drum printer.

2. Non-impact Printer

 Inkjet printer, thermal printer, laser printer, electromagnetic printer,

electrostatic printer.

Plotter

 It is an output device similar to a printer that uses a pen, pencil, marker or other writing
tool to make a design.
 Plotters are generally used to generate the map of building and shopping malls.
 A plotter is a computer printing device for printing vector graphics.
 In the past, plotters were widely used in applications such as Computer Aided Design
(CAD) and other print jobs.
 Though they have generally been replaced with wide-format conventional printers.

Speaker

 Speaker is an output device that receives the sound in the form of electric current from
the sound card and convert it into sound format.
 Speakers are used for listening to music.
 Computer speakers (multimedia speakers) are the speakers, which are attached internally
or externally to a computer system.
03 Storage Devices

This unit stores the data and instructions, intermediate results or the processed data and thus,
provides the relevant information whenever required by the other units of computer. It consists of
two types:

Primary Memory
It is considered to be the main memory of computer that stores the data which is currently in use
by the computer.

Types of Primary Memory:

1. RAM (Random Access Memory) is a volatile memory, which loses the data when the
power gets switched OFF. There are two types of RAM:

(i) Static RAM (SRAM)

(ii) Dynamic RAM (DRAM)
2. ROM (Read Only Memory) is a non-volatile memory, which retains the data even when
the power gets switched OFF.

Program and data that cannot be altered are stored in ROM. There are three types of ROM:
(i) Programmable ROM(PROM)
(ii) Erasable PROM(EPROM)
(iii) Electrically EPROM(EEPROM).

Secondary Memory

The computer system uses secondary memory to store data, program instruction and information.
It stores the data permanently. User can access or retrieve the data whenever required. Secondary
memory devices include as follows

1. Magnetic Storage It is the manipulation of magnetic fields on a medium in order to

record audio, video or other data.
o It includes hard disk drive, floppy disk and magnetic tape.
2. Optical Storage Optical storage is any storage type in which data is written and read
with a laser.
o It includes CD, DVD and Blu-ray disc.
3. Solid State Storage It is a type of storage technique that employs storage devices built
using silicon microchips based storage architecture.
 o It includes pen/flash drive, memory card.

Hard Disk Drive (HDD)

 It is a non-volatile and random access digital data storage device.

 HDD disk is used for storing and retrieving digital information using rotating disks (platters)
coated with magnetic material.
 All programs of a computer are installed in hard disk.
 It is a fixed disk i.e. cannot be removed from the drive.

Floppy Disk (Diskette)

 It is used to store data but it can store small amount of data and it is slower to access than hard
disks.
 Floppy disk rounds in shape and a thin plastic disk coated with iron oxide.
 Data is retrieved or recorded on the surface of the disk through a slot on the envelope.
 Floppy disk is removable from the drive.
 Floppy disk is available in three sizes; 8 inch, 5 1/4 inch and 3 1/2 inch.

Magnetic Tape

 These tapes are made of a plastic film-type material coated with magnetic materials to store
data permanently.
 Data can be read as well as recorded. It is usually 12.5 mm to 25 mm wide and 500 m to 1200 m
long.
 Magnetic tapes hold the maximum data, which can be accessed sequentially.
 They are generally used to store backup data or that type of data, which is not frequently used
or to transfer data from one system to another.

Compact Disc (CD)

 It is the most popular and the least expensive type of optical disc.
 A CD is capable of being used as a data storage device alongwith storing of digital audio.
  The files are stored on this particular contiguous sectors.

Digital Video Disc (DVD)

 DVD is also known as Super Density Disc (SDD) or Digital Versatile Disc (DVD).
 It is an optical disc storage media.
 DVDs offer higher storage capacity than CDs while having the same dimensions.

Blu-ray Disc

 It is an optical disc storage medium designed to re-capture the data normally in DVD format.
 Blu-ray disc (BD) contains 25 GB (23.31 GB) per layer space.
 The name Blu-ray disc refers to the blue laser used to the disc, which allows information to be
stored at a greater density than the longer-wavelength red laser used in DVDs.

Memory Cards

 These are the data storage devices in a chip shaped which can store the data in it.
 They are commonly used in many electronic devices, including digital cameras, mobile phones,
laptop, computers. They are small, recordable, easily portable and very light weighted.

Basic Units of Memory Measurements

1 Bit = Binary Digit (0 or 1)

4 Bits = 1 Nibble

8 Bits = 1 Byte = 2 Nibble

1024 Bytes = 1 KB (KiloByte)

1024 KB = 1 MB (MegaByte)
 1 Bit = Binary Digit (0 or 1)

1024 MB = 1 GB (GigaByte)

1024 GB = 1 TB (TeraByte)

1024 TB = 1 PB (PetaByte)

1024 PB = 1 EB (ExaByte)

1024 EB = 1 ZB (ZettaByte)

1024 ZB = 1 YB (YottaByte)

1024 YB = 1 BB (BrontoByte)

1024 BB = 1 GeopByte

04 Data Representation

Number System

 It defines a set of values that is used to represent quantity.

 Digital computers internally use the binary number system to represent data and perform
arithmetic calculations.

Types of Number System

1. Binary Number System

o This system is very efficient for computers, but not for humans.
o It contains only two unique digits 0’s and 1’s. It is also known as Base 2 system.
o e.g. (101011)₂
2. Decimal Number System
o The number system that we use in our day-to-day life is decimal number system.
o It consists of 10 digits from 0 to 9. It is also known as Base 10 system.
3. Octal Number System
 o It consists of 8 digits from 0 to 7. It is also known as Base 8 system.
4. Hexadecimal Number System
o It provides a shorthand method of working with binary numbers.
o There are 16 unique digits in this system: 0-9 and A-F (A=10, F=15).
o It is also known as Base 16 system.

Decimal to Binary

To convert decimal to binary, following steps are involved:

Step 1 Divide the given number by 2.

Step 2 Note the quotient and remainder. Remainder should be 0 or 1.
Step 3 If quotient ≠ 0, then again divide the quotient by 2 and back to step 2. If quotient = 0, then
stop the process.
Step 4 First remainder is called as Least Significant Bit (LSB) and last remainder is called as
Most Significant Bit (MSB).
Step 5 Arrange all remainders from MSB to LSB.

Example (43)₁₀ → (?)₂

2 43 1 → LSB

2 21 1

2 10 0

25 1

22 0

2 1 1 → MSB

Then, (43)₁₀ → (101011)₂

Binary to Decimal

To convert binary to decimal, following steps are involved:

Step 1 Multiply all binary digits by powers of 2.

Step 2 The power for integral part will be positive and for fractional part will be negative.
Step 3 Add all multiplying digits.
e.g. (110110)₂ → (?)₁₀

(110110)₂ = 1×2⁵ + 1×2⁴ + 0×2³ + 1×2² + 1×2¹ + 0×2⁰

= 32 + 16 + 0 + 4 + 2 + 0
= 54

(110110)₂ → (54)₁₀

Computer Codes

In computer, any character like alphabet, digit or special character is represented by collection of
1’s and 0’s in a unique coded pattern. The binary coding schemes that are most commonly used
are as follows:

 BCD (Binary Coded Decimal)

 ASCII (American Standard Code for Information Interchange)
 EBCDIC (Extended Binary Coded Decimal Interchange Code)

05 Operating System

Computer Software

It is a set of instructions, programs that are used to give command to the hardware. It is an
interface between user and computer. Softwares can be divided into two major categories:

 System software It consists of several programs which are directly responsible for controlling
and managing the individual hardware components of a computer system.
 Application software It is a computer software designed to help the user to perform singular or
multiple tasks.

Operating System

An operating system is a software, or a series of programs, which performs various types of

functions in order to manage and organize files.
Functions of an operating system are
(i) Process management (ii) Memory management
(iii) File management (iv) Input/output management

An OS can be classified as follows:

 Single-user Allows only one user at a time.

e.g. MS-DOS, Windows 9X.
 Multi-user Allows two or more users to run programs at the same time.
e.g. Unix, Linux, Windows 2000/7.
 Multi-tasking Allows more than one programs to be run concurrently.
e.g. Linux, Unix, Windows 95.
 Multi-processing Supports running a program on more than one CPU.
e.g. Unix, Windows NT/2000.
 Real-time Used for real-time based applications like satellite launch, weather-forecasting
etc.
e.g. Lynx, HP-RT.

Some Important Operating Systems

Some popular operating systems are as follows:

1. UNIX The first version of Unix was developed in 1969 by Ken Thompson and Dennis
Ritchie.
o It is primarily used to a server rather than a workstation and should not be used by
anyone who does not understand the system.
2. Apple Macintosh (Mac OS) It was introduced in January, 1984 by Steve Jobs and was
initially named as system software, which was later renamed as Mac OS.
3. LINUX The first Linux Kernel was released in September, 1991 by Linus Torvalds.
o It is an open source software. Linux is similar to Unix in operations. It is difficult to
understand by anyone.

4. Microsoft Windows It is an operating system, based on GUI, developed by Microsoft.

Microsoft first introduced an operating environment named Windows in November 1985
in response to the growing interest in GUIs.
5. MS-DOS (Microsoft-Disk Operating System) The DOS OS was developed by
Microsoft in 1980 for micro computers.
MS-DOS was the first operating system that run on PC developed by IBM corporation in
1981. DOS is a single user operating system.
It is only operating system which can be loaded in the main memory of the computer
using a single disk.
Mobile Operating System

 This OS operates on Smartphones, Tablets and Digital Mobile devices.

 It controls mobile devices and its design supports wireless communication and different types of
mobile applications.
 It has built-in support for mobile multimedia formats.

Some popular mobile operating systems are as follows:

1. Android It is a mobile OS developed by Google, which is based on Kernel (Main part of

operating system).
o It is basically designed for touch screen mobile devices like Tablets, Smartphones etc.
o Now-a-days, it is most common used in mobile phones.
o The latest version of Android is Pie which was released on 6th August, 2018.
2. iOS It is the popular mobile operating system developed by Apple Incorporation.
o This operating system is commonly used in Apple iPhone, iPod Touch, iPad etc.
o The latest version of iOS is iOS 11.4.1 which was released on 9th July, 2018.

06 - Microsoft Office

Microsoft Office was developed by Microsoft Inc in 1988. It is a collection of softwares, based
on specific purpose and mainly used in office work.

There are five packages of MS-Office

1. MS-Word (Word Processing Software)

2. MS-Excel (Spreadsheet Software)
3. MS-PowerPoint (Presentation Software)
4. MS-Access (Database Management Software)
5. MS-Outlook (E-mail Client)

Microsoft Word

MS-Word is a Word processing application which is one of the most important and widely used
applications found on computer.

 It provides tools for editing, formatting and printing of documents smaller than 45 Kb.
 The document can be a poster, report, letter, brochure, Web page, newsletter, etc. e.g.
WordStar, Notepad for Windows.
Features of Microsoft Word

The features of MS-Word are described below:

1. Text Editing
It provides editing, adding and deleting text, modification of text content i.e. cut, copy
and paste. When, we cut any text in our document, it will save in hard drive temporarily,
till we paste it on any other place.
2. Format Text
It offers to modify the text in any of the available hundreds of text designs. It formats text
in various styles such as bold, italic, underline, etc.
3. Indentation
It denotes the distance text boundaries and page margins.
It offers three types of indentation - positive, hanging and negative indent.
4. Page Orientation
It facilitates selection of typed text printed or visible in horizontal view or vertical view
on a specified size of the page.
Word offers Portrait - vertically oriented and Landscape - horizontally oriented.
5. Find and Replace
This feature allows flexibility and comfort to the user to replace a text with a substituted
text at all places.
6. Horizontal and Vertical Scroll Bars
They enable one to move up and down or left and right across the window.
o The horizontal scroll bar is located above the status bar.
o The vertical scroll bar is located along the right side of the screen to move up and down
the document.

Microsoft Excel

An electronic spreadsheet is used for analysing, sharing and managing information for
accounting purpose performing mathematical calculations, budgeting, billing etc.

 A spreadsheet is a matrix of rows and columns similar to an accounting ledger.

 The spreadsheet program also provides tools for creating graphs, inserting pictures and chart,
analysing the data etc.
e.g. Corel Quattro Pro, Snowball, Lotus-1-2-3, Apple Numbers etc.

Basics of Spreadsheet

The basic terms of spreadsheet are as follows:

 1. A spreadsheet is a software tool that lets one enter, calculate, manipulate and analyse set of
numbers.
2. The intersection of each row and column is called cell. A cell is an individual container for data.
It may hold:
o Numbers (Constants)
o Formulas (Mathematical equations)
o Text (Labels)
3. An array of cells is called a sheet or worksheet. A worksheet holds information presented in
tabular format with text.
4. A workbook is a document that contains one or more worksheet. Each new workbook has
created three worksheets by default.
5. A row is given a number that identifies it, it starts from 1, 2, 3, 4, 5,... so on.
6. A column is given a letter that identifies it starts from A, Z, AA … AZ, BA, BB … BZ so on.
7. An Active cell is a cell in which you are currently working.
8. A cell pointer is a cell-boundary that specifies which cell is active at that moment.
9. A formula is an equation that calculates the value to be displayed. A formula must begin with
equal to (=) sign.
10. A cell address is used to specify the intersecting of row and column of the letter and number on
worksheet.

Microsoft PowerPoint

The application software that can create professional looking visual aids is called presentation
graphics software.

 The presentation software is used for creation of the slides and to display the information in the
form of presentation of slides.
 A presentation software provides tools like editor that allows insertion and formatting of text
and methods for inserting and manipulating graphics images along with sound and visual
effects.

MS-Office Shortcut Keys

 Ctrl + B → Bold attribute

 Ctrl + I → Italic attribute
 Ctrl + U → Underline attribute
 Ctrl + C → to copy selected text to the clipboard
 Ctrl + X → to cut selected text
 Ctrl + V → to paste text from clipboard
  Ctrl + Z → to undo the last action
 Ctrl + Y → to redo the last action
 Ctrl + Home → to go to the start of the document
 Ctrl + End → to go to the end of the document
 F7 → to launch the Spelling and Grammar check
 F12 → to choose the Save As command (File menu)
 F10 → to activate the Menu Bar
 Ctrl + F2 → to choose the Print Preview command (File menu)
 Ctrl + N → to create a new document
 Ctrl + O → to open a document
 Ctrl + P → to print a document
 Ctrl + A → to select all
 Shift + F12 → to choose the Save command (File menu)
 Alt + F4 → to quit word
 Ctrl + H → to replace
 Ctrl + F → to find

07 - Networking

Computer networking relates to the communication between a group of two or more computers
linked together.

 When we communicate on a network, we share information or data through a communication

medium.
 E-mailing, instant messaging, and web pages all depend on communication that takes place
across an underlying computer network.

Some Benefits of Networking:

 Data and file sharing

 Software sharing
 Hardware sharing
 Reliability

Network Devices
These are required to amplify the signal to restore its original strength and provide an interface to
connect multiple computers in a network.

Some types of network devices are:

1. Repeater – Amplifies signals when transported over long distances so the signal can be as strong
as the original.
2. Hub – Functions like a repeater but with multiple ports to connect network channels.
3. Gateway – Joins two different network protocols together.
4. Switch – Forwards a data packet to a specific route by establishing a temporary connection
between the source and destination.
5. Bridge – Reduces traffic on a LAN by dividing it into two segments.
6. Modem – Converts digital signal to analog and vice-versa.

Types of Computer Networks

1. Local Area Network (LAN) – Covers a geographical area of 1 km to 10 km, usually within the
same building. All devices are connected to a main computer (server).
2. Metropolitan Area Network (MAN) – Designed for a town or city; used for hardware and
software resource sharing.
3. Wide Area Network (WAN) – Covers a large geographical area, connecting devices using radio
waves.

Communication Media

Refers to the medium used in a network to transmit data. It can be divided into:

1. Guided Media (Wired Technologies)

 Ethernet Cable (Twisted Pair) – Two independently insulated wires twisted to reduce crosstalk
and electromagnetic induction.
 Coaxial Cable – Contains a center wire surrounded by insulation and a grounded braided wire
shield.
 Fiber-Optic Cable – Contains optical fibers that carry light for data transmission.

2. Unguided Media (Wireless Technologies)

 Radio Wave Transmission – Uses ground waves and sky waves for communication.
 Microwave Transmission – Uses electromagnetic waves with small wavelengths (measured in
centimeters).
08 - Internet and Email

 Internet stands for International Network and began in the 1950s. Vint Cerf is known as the
"Father of the Internet."
 The Internet is a worldwide network of computers that can exchange information.
 The movement of data on the Internet is controlled by protocols.

Common Internet Protocols:

1. TCP/IP (Transmission Control Protocol/Internet Protocol)

2. HTTP (HyperText Transfer Protocol)
3. PPP (Point-to-Point Protocol)
4. FTP (File Transfer Protocol)
5. Telnet Protocol
6. WAP (Wireless Application Protocol)
7. Usenet Protocol

Internet Connections

1. Dial-up Connection – Uses a telephone line to connect to the Internet.

2. Broadband Connection – High-speed Internet, faster than dial-up, includes:
o DSL (Digital Subscriber Line)
o Cable Modem
o Fiber Optic
o BPL (Broadband over Power Line)
3. Wireless Connection – Uses a radio link between customer location and service provider.
o Wi-Fi (Wireless Fidelity)
o WiMAX (Worldwide Interoperability for Microwave Access)
o Mobile Wireless Broadband Service
o Satellite

Terms Related to the Internet

1. World Wide Web (WWW) – A system of Internet servers supporting hypertext and multimedia
for accessing multiple Internet protocols on one interface.
2. Web Page – A file containing text, images, and links to multimedia or other web pages, created
using HTML.
 3. Website – A group of related web pages linked with hyperlinks.
o Example:
 http://www.carwale.com → Website
 http://www.carwale.com/new/ → Web Page
 The first page of a website is called the Home Page.

Web Browser

 A software application to access the World Wide Web (WWW).

 Types:
o Text Web Browser (e.g., Lynx)
o Graphical Web Browser (e.g., Chrome, Firefox, Safari, Opera)

Web Address & URL

 Identifies the location of a webpage.

 Example:

arduino
CopyEdit
http://www.google.com/services/index.htm

o Protocol identifier: http://

o Domain name: google.com
o Directory: /services/
o Web page: index.htm

Domain Name System (DNS)

 Assigns unique addresses to computers on the Internet.

 Examples:
o .com → Commercial
o .edu → Educational
o .org → Non-Profit
o .gov → Government
o .in → India
o .au → Australia

Search Engines

 Websites that provide information retrieval.

 Examples: Google, Yahoo, Bing.
Email (E-mail)

 Electronic messaging system.

 Requires an email address (e.g., user@gmail.com).

Email Features

 Cc (Carbon Copy) – Sends to multiple recipients.

 Bcc (Blind Carbon Copy) – Recipients don’t see others in Bcc.
 Signature – Text added automatically at the end of emails.
 Attachment – Allows sending files (.doc, .pdf, .jpg).

Social Networking Sites (SNS)

 Online platforms for communication.

 Examples: Facebook, Twitter, LinkedIn, Instagram.

09 Computer Security
Definition

 Also known as Cyber Security or IT Security.

 A branch of Information Technology (IT) that protects computers from threats.

Four Primary Methods for Protection

1. System Access Control

2. Data Access Control
3. System and Security Administration
4. System Design

Sources of Cyber Attacks

 The most common and dangerous threat is virus attacks.

 Common attack sources:
o Downloadable programs
o Cracked software
o Email attachments
o Internet-based threats
o Booting from unknown CDs

Malware (Malicious Software)

 A broad term for software designed to harm or exploit computers.

 Includes viruses, worms, Trojan horses, rootkits, spyware, adware, etc.

Types of Malware

1. Virus
o A program that replicates itself without user knowledge.
o Common types: Boot sector virus, Macro virus, Resident virus, Polymorphic virus,
Direct action virus.
o Creeper (1971) – First known computer virus by Bob Thomas at BBN.
2. Worm
o A self-replicating program, similar to a virus but does not need a host file.
3. Trojan Horse
o Appears legitimate but gives unauthorized access.
o Unlike viruses, it does not replicate itself.
4. Spyware
o Secretly collects user information and sends it to third parties.
Other Threats to Computer Security

1. Spoofing – Unauthorized access by imitating a trusted source.

2. Hacking – Intruding into someone else’s computer/network.
3. Cracking – Breaking into computers using tools like password crackers, trojans, and viruses.
4. Phishing – Fraudulently acquiring sensitive information (e.g., passwords, credit card details).
5. Spam – Unsolicited emails (bulk messages).
6. Adware – Displays unwanted advertisements.
7. Rootkit – Malware that gains hidden admin access.

Solutions to Security Threats

1. Antivirus Software – Detects and removes malware (e.g., Avast, McAfee, Quick Heal).

Networking Concepts

Communication Methods

1. Satellite Communication – Provides long-distance communication links.

2. Infrared Wave Transmission – Uses electromagnetic radiation for short-range communication.
3. Bluetooth – Wireless technology for short-distance data transfer.

Network Related Terms

 Topology – Defines the physical layout of a network (e.g., Bus, Ring, Star, Tree, Mesh).
 Network Interface Card (NIC) – Hardware that connects computers to a network.
 Public Switched Telephone Network (PSTN) – Global landline telephone network (also called
Plain Old Telephone Service – POTS).
 Value Added Network (VAN) – Provides Electronic Data Interchange (EDI) services for
businesses.
 Integrated Service Digital Network (ISDN) – Combines circuit switching and packet switching
for data transmission.

Basics of Computers and Applications

Security Features

2. Digital Certificate – Ensures message security.

3. Digital Signature – Authenticates sender identity.
4. Firewall – Controls incoming and outgoing network traffic based on rules.
o Works with proxy servers to handle network requests.
5. Password – A secret code for user authentication.
6. File Access Permission – Determines user access levels (read, write, execute).