SEBA Class IX Computer Science Chapter 4- Introduction to Internet Notes PDF
SEBA Class 9 Computer Science Chapter 4-Introduction to Internet Notes PDF
Complete Notes • Simple Explanation • Important Concepts • Exam Preparation • PDF
📘 About This Chapter
Welcome to SEBA Class 9 Computer Science Chapter 4 – Introduction to Internet. In this chapter, we learn about the basic concepts of the Internet and how computers communicate with each other through networks.
The chapter explains Internet structure, different types of network topologies, client and server, network protocols, the history of the Internet, Internet connections, web browsers, the World Wide Web, URLs, search engines, electronic mail, chat and video conferencing.
4.1 What is Internet?
The Internet has become an essential part of our day-to-day life. It allows us to exchange information with each other very quickly.
The word Internet is derived from the words "interconnection" and "networks". A network is a collection of two or more interconnected computers or computing devices that can share information.
📖 Definition
The Internet is an interconnection of worldwide computer networks, often described as a network of networks.
The Internet consists of a large number of smaller heterogeneous computer networks connected together. It enables users to communicate, search for information, exchange files and access different online services.
4.2 Structure of Internet
The Internet does not have a single central structure or a central governing body. Because of this distributed structure, there is no single central point whose failure would bring down the entire Internet.
If the connection between two computers is lost, information can often be delivered through another available route.
💡 Important
The geometric structure showing how computers or devices are connected to one another in a network is called Network Topology.
Types of Network Topology
The chapter discusses the following five types of topology:
- Mesh Topology
- Star Topology
- Bus Topology
- Ring Topology
- Hybrid Topology
4.2.1 Mesh Topology
In a Mesh Topology, each device is connected directly to every other device through a separate link. A link carries data between the two devices connected to it.
🔗 Mesh Topology
Every computer is directly connected to the other computers in the network.
Advantages of Mesh Topology
- Failure of one link does not affect other links.
- Communication between other devices can continue.
- Failure of a link is comparatively easy to detect.
- Direct computer-to-computer connections provide better control over access.
- Less data travels through intermediate links.
Disadvantages of Mesh Topology
- A large number of cables or connection media are required.
- A large mesh network requires a high number of I/O ports in each computer.
- Adding a new device is difficult because it must be connected with existing devices.
4.2.2 Star Topology
In a Star Topology, all computers are connected to a central device. Instead of communicating directly with each other, computers communicate through the central device.
If one computer wants to send data to another computer, the data first goes to the central device, which then forwards the data to the intended destination.
Common central devices include a Hub, Switch or Router.
Advantages of Star Topology
- It is comparatively less expensive because each device needs only one connection to the central device.
- It is easier to install.
- New computers can be added easily.
- Failure of one link generally affects only one computer.
- A failed link can be easily identified.
Disadvantages of Star Topology
- The central device is a single point of failure.
- If the central device fails, the network can fail.
- The central device requires more attention because it controls the network.
4.2.3 Bus Topology
In a Bus Topology, there is a main cable to which all the computers in the network are connected through drop lines.
Since data is transmitted over the main cable, there is a limit on the number of drop lines that can be connected so that the data does not overflow in the main cable.
Advantages of Bus Topology
- Easy to install.
- Each computer needs to connect with the main cable.
- Fewer cables are required compared with mesh and star topology.
- Less maintenance is required because there is no central device.
Disadvantages of Bus Topology
- Fault detection can be difficult.
- There is a limit to the number of nodes that can be connected.
- The main cable can become a limitation as the network grows.
📝 Quick Revision
- Internet: Interconnection of worldwide computer networks.
- Topology: Geometric structure of a computer network.
- Mesh: Devices are directly connected with other devices.
- Star: Devices communicate through a central device.
- Bus: Devices are connected to a common main cable.
🎯 Exam Tip
For examinations, learn the definition, advantages and disadvantages of each network topology. Pay special attention to the difference between Mesh, Star and Bus topology.
➡ Continue to Part 2
In Part 2, we will cover:
- Ring Topology
- Hybrid Topology
- Client and Server
- Network Protocol
- History of the Internet
4.2.4 Ring Topology
In a Ring Topology, each computer is connected with two other computers, one on each side. These direct connections form a closed ring, and therefore it is called ring topology.
In this topology, two adjacent computers can communicate directly. However, if a computer needs to communicate with a non-adjacent computer, the data is forwarded through the other computers in the ring until it reaches the intended destination.
🔄 Ring Topology
Each computer is connected to two neighbouring computers, forming a closed ring.
Advantages of Ring Topology
- It is easy to install.
- No central device is required.
Disadvantages of Ring Topology
- A link failure can break the ring and may cause the entire network to fail.
- Each device has to remain active; otherwise, data may not be forwarded through an inactive device.
4.2.5 Hybrid Topology
A combination of two or more different network topologies is known as a Hybrid Topology.
For example, a network may combine Star Topology and Ring Topology. Such a combination creates a hybrid topology.
📖 Definition
Hybrid topology is formed when two or more different types of network topologies are connected together.
The textbook notes that there are no straightforward advantages and disadvantages of hybrid topology because they depend on the different networks that are combined. :contentReference[oaicite:1]{index=1}
📊 Quick Comparison of Network Topologies
| Topology | Main Feature | Central Device |
|---|---|---|
| Mesh | Every device has a direct connection with other devices. | No |
| Star | All computers are connected to a central device. | Yes |
| Bus | All computers are connected to a main cable. | No |
| Ring | Each computer is connected to two neighbouring computers. | No |
| Hybrid | Combination of two or more different topologies. | Depends on design |
4.3 Client and Server
In computing terminology, client and server refer to computers that are used for different purposes.
A computer can be configured to behave like a server, and the same computer can also be configured to behave like a client depending on how it is used.
Client
A client is generally a comparatively lower-capacity computer that accesses a server through a network.
For example, when we browse a website, our computer or device can act as a client while accessing information stored on a server.
Server
A server is generally a higher-capacity computer that can store and provide a wide variety of resources to client computers.
Examples of Servers
- Application Server
- File Server
- Web Server
- Database Server
- Print Server
- Proxy Server
💡 Remember
Client requests or accesses resources, while a server provides or stores resources for clients.
4.4 Protocol
A network protocol is an established set of rules that determines how data is transmitted between different computers in a network.
Protocols can be considered a common language for computers. They allow connected computers to communicate with one another even when there are differences in their internal processes, structure or design.
Common Network Protocols
| Protocol | Use / Association |
|---|---|
| HTTP | Used for web communication. |
| HTTPS | Used for secure web communication. |
| FTP | Used for file transfer. |
| SMTP | Used for sending email. |
📖 Definition
A protocol is a set of rules that determines how data is transmitted and communicated between computers on a network.
4.5 History of the Internet
The first workable prototype of the Internet, known as ARPANET (Advanced Research Projects Agency Network), came into existence in the late 1960s.
ARPANET was started by the U.S. Department of Defense. On October 29, 1969, ARPANET delivered its first message.
The first computer involved was located at a research lab at the University of California, Los Angeles, while the second was located at Stanford.
ARPANET adopted TCP/IP in 1983. After this, more computer scientists began to form networks of networks, helping establish the foundation of the modern Internet.
The invention of the World Wide Web (WWW) in 1990 by Tim Berners-Lee helped the Internet appear in a more recognizable form. :contentReference[oaicite:2]{index=2}
🕐 Important Timeline
| Year / Period | Event |
|---|---|
| Late 1960s | ARPANET prototype was developed. |
| 1969 | ARPANET delivered its first message. |
| 1983 | ARPANET adopted TCP/IP. |
| 1990 | World Wide Web was invented by Tim Berners-Lee. |
4.6 Internet Connection
An Internet connection refers to the link that connects a device to the Internet.
Internet connections are provided by Internet Service Providers (ISPs). Examples of popular ISPs in India mentioned in the textbook include Reliance Jio, Airtel and BSNL.
An ISP can provide Internet connectivity to consumers in different ways.
🌐 Two Main Types
- Wired Internet Connection
- Wireless Internet Connection
4.6.1 Wired Internet Connection
In a wired Internet connection, a physical wire is laid from the ISP's server to the consumer's computer or network.
Different types of cables can be used for this purpose. Each type of cable has its own limitations in terms of data transfer rate and data transfer range.
Types of Wired Connection Cables
| Property | Twisted Pair | Co-axial Cable | Optical Fibre Cable |
|---|---|---|---|
| Maximum Transfer Rate | 10 Gbps | 100 Mbps | More than 100 Gbps |
| Maximum Transfer Range | 100 m | 500 m | 2 KM and farther |
Properties of different types of cables given in the textbook.
Dial-Up
Dial-up is an older technology used to provide Internet connection through a telephone line.
A modem converts analog signals into digital signals and vice versa. The modem connects to the Internet Service Provider (ISP).
The technology provides a maximum speed of approximately 56 kbps. During the connection, the telephone line remains busy until the connection is closed.
Digital Subscriber Line (DSL)
DSL provides high-speed Internet access through existing telephone networks.
The telephone and DSL modem can work at the same time.
Types of DSL
- Symmetrical DSL
- Asymmetrical DSL
Symmetrical DSL provides equal bandwidth for uploading and downloading. Asymmetrical DSL provides more downstream bandwidth and less upstream bandwidth.
In a DSL connection, conversion between digital and analog signals is not required.
Integrated Services Digital Network (ISDN)
ISDN is a digital transmission system used to transmit voice and data through a telephone line.
In terms of speed, ISDN is slower than DSL, but an ISDN connection is more convenient and faster than a dial-up connection.
Cable Internet
Cable Internet access is a form of broadband Internet access that uses the same infrastructure as cable television.
It can be used in areas where cable Internet providers are available. Cable Internet providers share the main connection with consumers using coaxial cable.
🎯 HSLC / School Exam Tip
- Learn the differences between the five network topologies.
- Remember the definitions of client, server and protocol.
- Remember the important ARPANET timeline.
- Learn the difference between wired and wireless connections.
- Remember the basic properties of twisted-pair, coaxial and optical-fibre cables.
➡ Continue to Part 3
Part 3 will cover the remaining Internet connection types and the important web concepts from the chapter:
- Wireless Internet Connection
- Satellite Connection
- Wi-Fi
- WiMAX
- Web Browser
- World Wide Web (WWW)
- Website
- Uniform Resource Locator (URL)
4.6.2 Wireless Internet Connection
In a Wireless Internet Connection, there is no physical wire connecting the computer or device to the Internet. Data is transmitted through wireless signals.
Wireless Internet connections are useful because devices can access the Internet without being physically connected through cables.
Major Types of Wireless Internet Connection
- Satellite Internet
- Wi-Fi
- WiMAX
Satellite Internet
A Satellite Internet Connection provides Internet access through communication with satellites. It is particularly useful in locations where conventional wired Internet infrastructure is not easily available.
📡 Remember
Satellite Internet uses a satellite-based communication system instead of a direct physical cable connection.
Wi-Fi
Wi-Fi is a wireless networking technology that allows devices to connect to a Wi-Fi network using radio-frequency signals.
Computers, smartphones, tablets and other devices can connect to the Internet through a Wi-Fi network when the network is connected to an Internet service.
Features of Wi-Fi
- Uses wireless signals.
- Does not require a physical cable between the device and Wi-Fi network.
- Allows multiple devices to connect to the same network.
- Commonly used in homes, schools, offices and public places.
WiMAX
WiMAX stands for Worldwide Interoperability for Microwave Access. It is a wireless broadband technology designed to provide Internet access over a relatively large area.
📖 Full Form
WiMAX = Worldwide Interoperability for Microwave Access
📊 Wired vs Wireless Internet Connection
| Wired Internet | Wireless Internet |
|---|---|
| Uses physical cables. | Uses wireless signals. |
| Requires a physical connection. | Does not require a physical cable to the device. |
| Examples include Dial-up, DSL, ISDN and Cable Internet. | Examples include Satellite, Wi-Fi and WiMAX. |
4.7 Web Browser
A Web Browser is a computer program used to access, display and navigate between web pages on the Internet.
When a user enters the address of a website, the browser retrieves the required web page and displays its content on the screen.
📖 Definition
A web browser is software used to access and navigate websites and web pages on the Internet.
Examples of Web Browsers
- Google Chrome
- Mozilla Firefox
- Microsoft Edge
- Safari
- Opera
What Can a Web Browser Do?
- Open web pages.
- Navigate between websites.
- Display text, images and other web content.
- Access information available on the World Wide Web.
4.8 World Wide Web (WWW)
The World Wide Web (WWW) is a collection of web pages and other web resources stored on web servers and made accessible through the Internet.
Web resources can be accessed using a web browser. Communication between the browser and web server takes place using web protocols such as HTTP.
💡 Full Form
WWW = World Wide Web
Important Point
The Internet and the World Wide Web are related but they are not exactly the same thing. The Internet is the worldwide network, while the WWW is a collection of web resources accessed through that network.
4.9 Website
A website is a collection of related web pages containing information and other digital resources.
A website may contain:
- Text
- Images
- Videos
- Audio
- Databases
- Links to other web pages
The web pages of a website are connected with one another through hyperlinks.
📖 Definition
A website is a collection of related web pages connected through hyperlinks and stored on web servers.
Web Page vs Website
| Web Page | Website |
|---|---|
| A single page or document on the Web. | A collection of related web pages. |
| Usually contains specific information. | Contains multiple related pages and resources. |
| Can be part of a website. | Contains one or more web pages. |
4.10 Uniform Resource Locator (URL)
A Uniform Resource Locator (URL) is the address used to identify and locate a particular resource on the Internet.
A URL can identify resources such as web pages, images, files and other resources available on the Web.
📖 Full Form
URL = Uniform Resource Locator
Example of a URL
https://www.example.com/index.html
Main Parts of a URL
| Part | Example | Purpose |
|---|---|---|
| Protocol | https | Specifies the communication protocol. |
| Domain | example.com | Identifies the website or domain. |
| Path / File | index.html | Identifies a particular resource or page. |
Hyperlink
A Hyperlink is a link that connects one web resource or web page to another. By clicking a hyperlink, a user can navigate to another page, website, file or resource.
🔗 Remember
Hyperlinks make navigation between different web pages and resources possible.
🌐 Internet Concepts at a Glance
| Term | Meaning |
|---|---|
| Internet | Worldwide interconnection of computer networks. |
| Browser | Software used to access and navigate web pages. |
| WWW | Collection of web pages and web resources. |
| Website | Collection of related web pages. |
| URL | Address used to locate a web resource. |
| Hyperlink | Link connecting one web resource to another. |
🎯 Exam Tip
- Remember the full forms of WWW, URL and WiMAX.
- Know the difference between Internet and WWW.
- Learn the definition of a web browser.
- Remember examples of popular web browsers.
- Understand what a website and hyperlink are.
➡ Continue to Part 4
The final part will cover the remaining important Internet services:
- Search Engine
- Electronic Mail (Email)
- Components of an Email
- Email Folders
- Chat
- Video Conferencing
- Important Keywords
- Chapter Summary
- Frequently Asked Questions
- HSLC / Exam Preparation Tips
- Embedded Chapter 4 PDF
4.11 Search Engine
A Search Engine is a software system that helps users find information and web content available on the Internet.
Instead of visiting websites one by one, users can enter keywords or search terms into a search engine to find relevant information.
Examples of Search Engines
- Bing
- Yahoo!
🔍 Remember
A search engine helps users search for information available on the Internet.
How Does a Search Engine Work?
A search engine generally performs three important functions:
- Crawl - Search engines discover and collect information from web pages.
- Index - The collected information is organized and stored in an index.
- Rank - The search engine arranges the results according to their relevance to the search query.
Discover web pages
Store and organize information
Arrange relevant results
4.12 Electronic Mail (Email)
Electronic Mail, commonly known as Email, is a method of sending and receiving electronic messages over the Internet.
Email allows users to communicate and exchange information electronically. Messages can also contain attachments such as documents, images and other files.
📧 Definition
Email is a method of sending and receiving electronic messages over the Internet.
Email Protocols
Different protocols are used for sending and receiving email messages. The chapter identifies the following protocols:
- SMTP - Simple Mail Transfer Protocol
- POP - Post Office Protocol
- IMAP - Internet Message Access Protocol
| Protocol | Purpose |
|---|---|
| SMTP | Used for sending email messages. |
| POP | Used for receiving email messages. |
| IMAP | Used for accessing email messages. |
4.12.1 Email Address
Every email account has an Email Address. An email address contains two main parts separated by the @ symbol.
For example:
| Part | Example | Meaning |
|---|---|---|
| Username | student | Identifies the user. |
| @ Symbol | @ | Separates the username from the domain. |
| Domain | gmail.com | Identifies the email service/domain. |
4.13 Components of an Email
An email message contains several important components. The major components include:
- Subject
- Sender (From)
- Date
- Recipient (To)
- CC (Carbon Copy)
- BCC (Blind Carbon Copy)
- Attachment
| Component | Purpose |
|---|---|
| Subject | Shows the topic or purpose of the email. |
| From | Shows the sender of the email. |
| Date | Shows the date associated with the email. |
| To | Shows the main recipient of the email. |
| CC | Carbon Copy. Used to send a copy to additional recipients. |
| BCC | Blind Carbon Copy. Used to send a copy without revealing the BCC recipients to other recipients. |
| Attachment | Allows files to be included with an email. |
4.14 Email Folders
Email services organize messages into different folders. These folders help users manage their emails efficiently.
| Folder | Purpose |
|---|---|
| Inbox | Contains received emails. |
| Compose | Used to create a new email message. |
| Sent | Contains emails that have been sent. |
| Drafts | Contains unfinished or saved email messages. |
| Spam | Contains unwanted or unsolicited emails. |
| Trash | Contains deleted email messages. |
⚠️ Important
Unsolicited bulk emails are generally placed in the Spam folder.
4.15 Chat
Chat is a method of real-time communication through text messages over the Internet.
It allows people in different locations to exchange messages almost instantly.
💬 Definition
Chat is the real-time exchange of text messages over the Internet.
Features of Chat
- Communication takes place in real time.
- Messages can be exchanged over the Internet.
- People in different locations can communicate with each other.
4.16 Video Conferencing
Video Conferencing is a method of live audio and video communication between people located in different places.
It allows participants to communicate with both sound and video through the Internet.
🎥 Definition
Video conferencing provides live audio and video communication between people in different locations.
Examples
- Google Meet
- Zoom
- Webex
Chat vs Video Conferencing
| Chat | Video Conferencing |
|---|---|
| Primarily involves text communication. | Provides live audio and video communication. |
| Messages are exchanged through text. | Participants can communicate using audio and video. |
| Useful for text-based real-time communication. | Useful for meetings, classes and live communication. |
📚 Important Keywords
| Keyword | Meaning |
|---|---|
| Internet | A worldwide network of interconnected computer networks. |
| Computer Network | A connection of computers and devices for communication and resource sharing. |
| Topology | The arrangement or structure of devices in a network. |
| Client | A computer that requests services or resources. |
| Server | A computer that provides services or resources to clients. |
| Protocol | A set of rules used for communication between computers. |
| ARPANET | An early network that played an important role in the development of the Internet. |
| ISP | Internet Service Provider. |
| WWW | World Wide Web. |
| Hyperlink | A link that connects one web resource to another. |
| URL | Uniform Resource Locator, the address used to locate a web resource. |
| Search Engine | A system used to search for information on the Internet. |
| Electronic messages sent and received over the Internet. | |
| Chat | Real-time exchange of text messages over the Internet. |
| Video Conferencing | Live audio and video communication between people in different locations. |
📝 Chapter 4 Summary
- A computer network connects computers and other devices.
- Network topology describes the arrangement of devices in a network.
- Client and server computers perform different roles in a network.
- A protocol provides rules for communication between computers.
- ARPANET played an important role in the development of the Internet.
- Internet connections can be wired or wireless.
- A web browser is used to access and navigate websites.
- The WWW is a collection of web pages and web resources.
- A website consists of related web pages.
- A URL identifies and locates a web resource.
- A search engine helps users find information on the Internet.
- Email is used to send and receive electronic messages.
- Email contains components such as Subject, From, To, CC, BCC and Attachment.
- Email services organize messages into folders such as Inbox, Sent, Drafts, Spam and Trash.
- Chat allows real-time exchange of text messages.
- Video conferencing provides live audio and video communication.
🎯 Exam Preparation Tips
- Learn the definitions of important terms such as Internet, Protocol, Client, Server, WWW, Website and URL.
- Remember the different types of network topologies and their characteristics.
- Revise the history of the Internet, especially ARPANET, TCP/IP and WWW.
- Understand the difference between Wired and Wireless Internet Connections.
- Remember examples of popular Web Browsers.
- Learn the components and structure of a URL.
- Understand the three major functions of a search engine: Crawl, Index and Rank.
- Learn the important email protocols: SMTP, POP and IMAP.
- Remember the different Email Components and Email Folders.
- Understand the difference between Chat and Video Conferencing.
⚡ Quick Revision
| Question | Answer |
|---|---|
| What is WWW? | World Wide Web |
| What is URL? | Uniform Resource Locator |
| What is ISP? | Internet Service Provider |
| What does WiMAX stand for? | Worldwide Interoperability for Microwave Access |
| Who invented the World Wide Web? | Tim Berners-Lee |
| What are the three functions of a search engine? | Crawl, Index and Rank |
| What is used for sending email? | SMTP |
| Where are unwanted bulk emails normally placed? | Spam |
| What is Chat? | Real-time exchange of text messages over the Internet. |
| What is Video Conferencing? | Live audio and video communication between people in different locations. |
📘 Chapter 4 PDF Notes
Read the complete chapter directly below.
🧠 Test Your Knowledge
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🎯 Practice Chapter 4 MCQs🎓 Class IX Computer Science – Chapter 4
Introduction to Internet
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