CBSE Class 10 Computer Applications

The Internet and the web are different things

The Internet is the global network of networks: millions of computers, phones, servers and routers joined by cables, fibre, satellites and radio links, all agreeing to exchange data using a common set of rules called protocols. The Internet carries many services, including email, file transfer, video calls and online games.

The World Wide Web (WWW, or the web) is one of those services. It is a collection of linked documents and other resources, such as pages, images and videos, that can be reached over the Internet using a web browser. Tim Berners-Lee proposed it at CERN in 1989 and built the first working version in the early 1990s. The network already existed by then, which is why the two words are not interchangeable: sending an email does not use the web, but opening a page in a browser does.

The web rests on three ideas: every resource has an address (a URL), the resources are requested and delivered using a protocol (HTTP or HTTPS), and the pages are written in a markup language (HTML) that lets one page link to another.

Web servers and web clients

A web server is a computer, together with the software running on it, that stores web content and sends it out when asked. It listens for requests, finds the file or builds the page that was asked for, and sends back a response. If it cannot find what was asked for, it sends back an error message instead. Apache HTTP Server, Nginx and Microsoft IIS are examples of web server software.

A web client is the program, running on the user's device, that asks for content and shows what comes back. The usual web client is a web browser. The client sends a request to the server, receives the response and displays it, and it also handles what the user does on the page, such as clicking a link or submitting a form.

This pattern, in which one side asks and the other answers, is called the client-server model. A single server usually answers many clients at the same time.

Web pages, web sites and web browsers

A web page is a single document on the web, written in HTML and shown in a browser. It can contain text, images, audio, video, tables, forms and links to other pages.

A web site is a collection of related web pages kept together under one domain name and usually owned by one person or organisation. The first page a visitor normally sees is the home page, and it links to the other pages of the site.

A web browser is the application used to open and read web pages. It sends requests to web servers, receives the HTML and other files, and renders them into the page the user sees. Chrome, Firefox, Microsoft Edge, Safari and Opera are browsers. A browser also stores bookmarks and history, can hold several pages open in tabs, and checks whether a connection is secure.

Blogs

A blog (short for web log) is a web site or part of one where a person or an organisation publishes articles, called posts, on a topic or topics. The newest post is usually shown first, and readers can often add comments. Blogs started as personal online diaries and are now also used by businesses, teachers and news organisations.

Newsgroups

A newsgroup is an online discussion forum on one subject, such as a hobby or a technical topic. A person posts a message to the group, and other members read it and reply, so a thread of messages builds up. Newsgroups are older than the web and were carried by a system called Usenet. Some are moderated, meaning a person checks posts before they appear. Web-based discussion groups now do much the same job.

HTML

HTML (HyperText Markup Language) is the language used to write web pages. It describes the structure and content of a page by surrounding text with tags, which tell the browser what each part is: a heading, a paragraph, a list, an image or a link. HTML is a markup language, not a programming language, because it describes a document and does not contain instructions to calculate anything. The word hypertext refers to text that contains links to other documents, and it is what makes the web a web. HTML is covered in detail in its own notes.

How a page reaches the screen

1. The user types a web address into the browser, or clicks a link.
2. The browser finds the server's address on the Internet and sends it a request.
3. The web server locates the page and sends it back to the browser.
4. The browser reads the HTML, requests any images, styles or other files the page refers to, and displays the finished page.