What is the Internet? Structure
A network is two or more computers joined so they can share data. The Internet is a network of networks that covers the whole world.
- Devices: phones, laptops, smart TVs.
- Router: a box that joins the devices in a home or school and sends data the right way.
- ISP (Internet Service Provider): the company that connects you, by cable, fibre, mobile data or satellite.
- Backbone: very fast fibre-optic cables, many under the sea, that join countries.
Packets and IP addresses
Data is cut into packets of about 1.5 KB. Each packet carries the sender's and receiver's IP address (a number like 203.0.113.7) and a sequence number. Packets may travel by different roads. At the end they are put back in order. Rules for this are called protocols (TCP/IP).
DNS: names into numbers
People remember names, computers use numbers. The Domain Name System (DNS) turns a name such as example.org into its IP address.
Internet services
Many services run on the Internet. Most use the client-server idea: your app (client) asks, a server answers.
- World Wide Web: pages linked together, opened in a browser using a URL like https://example.org/page.
- Email: messages to an address like name@example.org.
- Video calls and chat: live talking and messaging.
- Cloud storage: keep files on online servers and open them from any device.
- Streaming, online shopping, banking, e-learning.
The web is not the same as the Internet: the web is one service that runs on the Internet.
Searching the web smartly
- Decide what you need. Pick 2 to 4 keywords (boiling point water, not a long sentence).
- Use tools: "quotes" for an exact phrase, a minus sign to remove a word (jaguar -car), site: to search one site (site:who.int malaria).
- Look past the first result and ads.
- Check each source: Who wrote it? Is it recent? Does it give evidence? Do other good sites agree? Government, university and well-known reference sites are usually reliable; anonymous posts need care.
- Note the source (site name, link, date) when you use the information.
Rules of safe and fair use
- Privacy: never share passwords, home address, phone number or school name with strangers.
- Strong passwords: long, mixed, different for each site.
- Netiquette: be polite; no bullying; think before you post, because posts can stay forever.
- Copyright: other people's text, pictures and music belong to them. Give credit and use only what is allowed.
- Scams: do not click strange links or download from unknown sites. Tell a trusted adult if something feels wrong.
Saving files in different formats and printing
A file format is the way data is stored, shown by the extension after the dot.
- .txt: plain text only. .docx/.odt: text with styles you can still edit.
- .pdf: looks the same on every device; good for sharing and printing.
- .jpg: photos (small, some quality lost). .png: drawings and screenshots (sharp, no loss).
- .mp3: sound. .mp4: video.
Use Save As to choose a name, a folder and a format. Before printing, use Print preview: choose the printer, pages (e.g. 2-4), number of copies, colour or black-and-white, and portrait or landscape. Printing to PDF makes a file instead of paper.
Try it: in the 3D and at home
In the last 3D step, set the file to 10 MB and the speed to 20 Mbps. Predict the time first: 10 × 8 = 80 megabits, 80 ÷ 20 = 4 s. Then check. At home, search the same question three ways (a sentence, keywords, keywords in quotes) and compare the first results.
Key formulas and definitions
- Internet: a worldwide network of networks
- Packet: a small piece of data with addresses and a number
- IP address: the number that identifies a device on the Internet
- DNS: turns domain names into IP addresses
- ISP: the company that connects you to the Internet
- Download time (s) ≈ file size (MB) × 8 ÷ speed (Mbps)
- URL: the full address of a web page, e.g. https://example.org/page
Worked examples
1. Name the parts of the URL https://www.example.org/maths/index.html.
https = protocol (secure web); www.example.org = domain name; /maths/index.html = path to the page on the server.
2. A 20 MB file is downloaded at 40 Mbps. About how long does it take?
20 MB × 8 = 160 megabits. 160 ÷ 40 = 4 seconds.
3. Rewrite the search "what is the height of the tallest mountain in the world" with better keywords.
tallest mountain height (or "Mount Everest" height). Short keywords give focused results.
4. You must send a finished project that must look the same on every computer and be printed. Which format?
PDF, because it keeps layout and fonts fixed on every device and prints exactly as seen.
Common mistakes
- Thinking the Internet and the World Wide Web are the same: the web is only one service on the Internet.
- Trusting the first search result without checking who wrote it and when.
- Mixing up MB (megabytes) and Mb (megabits): 1 byte = 8 bits, so multiply MB by 8.
- Saving a photo of a drawing as .jpg and wondering why the lines look blurry; use .png for sharp images.