Internet, Networking & Cyber Security

A computer network is a group of computers and devices connected so that they can share data, files, printers and an Internet connection. Each device on the network is a node. Networking saves money (one printer for a whole office), saves time (files move in seconds), and keeps data in one safe place. Every network needs three things: devices to connect, a medium to carry the signal (cable or air), and protocols, the agreed rules by which the devices talk.

In a full mesh of n computers every pair needs its own link, so the number of links is n(n-1)/2. For 5 computers that is 5 x 4 / 2 = 10 links; for 6 computers it is 6 x 5 / 2 = 15. In a star of n nodes you need only n links (one to the centre), which is why star is cheap. A tree topology is several star networks joined by a bus-like backbone; a hybrid topology mixes two or more types.

The Internet is a worldwide network of interconnected networks, linking billions of computers and devices through standard rules called protocols, mainly TCP/IP. No single company or country owns it. Do not confuse it with the World Wide Web (WWW): the Internet is the road system, the Web is one of the services running on it (a collection of web pages reached through HTTP). Email, FTP and video calls also travel on the same Internet but are not the Web.

An ISP (Internet Service Provider) is the company that gives you access to the Internet, normally for a fee: for example BSNL, Airtel or Jio in India. The word broadband simply means a high-speed, always-on connection. Downloading is receiving a file from a remote server to your device; uploading is sending a file from your device to a server; streaming is playing audio or video as it arrives, without saving the whole file first.

DNS (Domain Name System) is the Internet's phone book. People remember names like www.example.org, but computers talk in IP addresses. DNS translates the domain name into the IP address of the server. Without DNS you would have to type numbers for every website. DHCP, a different service, hands out IP addresses to devices automatically.

A domain name has levels read from right to left. In www.nasa.gov, gov is the top-level domain (TLD), nasa is the second-level domain and www is a subdomain. Domain names are managed by ICANN (Internet Corporation for Assigned Names and Numbers) through registrars, and web standards come from the W3C (World Wide Web Consortium).

The World Wide Web (WWW) is a service on the Internet: a huge collection of linked pages called web pages, joined by hyperlinks. It was proposed by Tim Berners-Lee at CERN in 1989 and opened to the public in the early 1990s. Pages are written in HTML, stored on a web server, and fetched by a web browser using the HTTP or HTTPS protocol. A group of related pages under one domain name is a website; its first page is the home page.

A URL (Uniform Resource Locator) is the full address of one resource on the Web. Read it from left to right and it answers three questions: how to talk (protocol), whom to talk to (host), and what to ask for (path). Take https://www.example.org/about: https is the protocol (also called the scheme), www.example.org is the host name, example.org is the domain name, .org is the Top-Level Domain (TLD), and /about is the path to the page.

A web browser is client software that sends a request to a web server and then renders (draws) the reply as a page on your screen. A search engine is a website that locates pages for you. You open a search engine inside a browser, just as you look up a shop in a directory while sitting in a car: the car is the browser, the directory is the search engine.

Cloud computing means using servers on the Internet, not your own computer, to store data and run programs, usually paid for as you use them. Google Drive, OneDrive and Dropbox store files in the cloud; the service models are SaaS (ready software, such as Gmail), PaaS (a platform to build apps) and IaaS (raw servers and storage).

Electronic mail (email) is the exchange of messages between people over a network. It is older than the Web: Ray Tomlinson sent the first network email in 1971 and chose the @ sign to separate the user name from the computer name. To use email you need three things: an Internet connection, an email account, and the recipient's email address. You do not need the recipient's IP address; the mail servers find it through DNS.

An email address has two parts joined by @ (read as 'at'): username@domain. The first part is the username (it identifies the mailbox); the part after @ is the domain name of the mail provider or organisation. In anil.sharma@example.com, anil.sharma is the username and example.com is the domain. An address has exactly one @.

Webmail (Gmail, Outlook.com, Yahoo Mail, Proton Mail, GMX) is used through a browser after logging in with a username and password. An email client (Microsoft Outlook, Mozilla Thunderbird) is a program installed on your device that sends, receives and manages mail, and can hold several accounts in one window. Attachments travel using the MIME standard. As of 2025 Gmail allows attachments up to 25 MB in total per message; larger files are shared as Drive links.

Email etiquette (netiquette): write a clear, short subject line; greet politely; keep the message focused; use simple black text in a standard font, with bold or italics only for key words; never WRITE IN CAPITAL LETTERS, which reads as shouting; check spelling; mention and name your attachments; think before using Reply All. Ordinary email is not encrypted end to end, so passwords and bank details should never be sent in it, because plain mail can be intercepted.

Cyber security is the protection of computers, networks and data from theft, damage and unauthorised access. Its aims are summed up in the CIA triad: Confidentiality (only the right people can read the data), Integrity (data is not changed secretly) and Availability (the data and service are there when needed). Every threat in this topic attacks one of these three, and every safeguard defends one.

Malware (malicious software) is any program written to harm or spy on a system. The big question for the exam is always: how does it spread, and does it need you to do something? A virus needs a host file and your action to run. A worm runs alone and spreads by itself over a network. A Trojan pretends to be useful software and does not replicate.

Online banking is safe only when you and the bank both do your part. The bank gives you HTTPS, OTP and two-factor authentication; you must give it a correct URL, a private device and a secret that stays secret. Nearly every question on this topic asks one thing: which habit closes the door to the fraudster, and which leaves it open?

Cyber crime is any crime in which a computer or network is the tool, the target or the place. Common forms: hacking, phishing and online financial fraud, identity theft (using someone else's personal details), cyberstalking and cyberbullying (online harassment), spreading malware, data theft, and cyber terrorism. In India you can report any of these at the National Cyber Crime Reporting Portal, cybercrime.gov.in, or by calling the helpline 1930; report a financial fraud at once, because the first hours matter most.