1.2 The Internet

A giant network of computers

The Internet is not the same as the Web. The Internet is bigger, older, and more varied.

Imagine how roads are interconnected throughout the world: small streets connect to city lanes that turn into regional roads who then merge with national and international highways. You can drive from your house to any other house in the world1. There is no actual center in this road network either.

The Internet is similar. But instead of roads, it’s cables. And instead of houses, it’s computers. And instead of cars traveling on this network, it’s information.

It was invented in 1969 to connect computers across the US. Nowadays, billions of devices (including PCs, laptops, mobile phones, TVs, fridges…) are interconnected.

Client and Server

Usually, a connection on the Internet takes place between 2 computers only:

  • one that has the information (the server)
  • one that wants it (the client).

A client is a program that can take up many forms:

  • a Web browser (like Firefox)
  • an email client (like Outlook)
  • a messenger app (like Whatsapp)
  • a video streaming service (like Netflix)

Each of these programs will retrieve information from a server, where something is stored (a website, your emails, messages, movies). Although client programs also send information to the server, they usually don’t store it, while servers do.

A server can be considered a dedicated computer always connected to the Internet, whose sole purpose is to deliver content.

Although any device connected to the Internet can be both a client and a server at the same time, most devices we use are considered clients, because we only retrieve data, and don’t deliver any.

IP Address

Like every house has a specific and unique postal address, each computer connected to the Internet is given an IP address, in order to be identified on the network.

An IP address usually looks like a combination of 4 numbers:


Although IP addresses are useful for computers to tell each other apart thanks to their uniqueness, they are hard to read and remember for us humans.

That is why domains were created in 1985. They associate an IP address like with a string of text like wikipedia.org. As a result, both are interchangeable: you can go to or https://wikipedia.org and end up on the exact same website.

A domain has 3 parts, that are read from right to left:

  • Top-Level Domain (or TLD): there are generic ones (.com, .org, .net) and country-specific ones (.us, .nl, .fr).
  • Domain name: a name like wikipedia or marksheet, that can include letters, numbers, but no space or dot.
  • Subdomain (optional). Although this 3rd part is optional, most websites use www as the default subdomain.

Think of domains as a way to name computers connected to the Internet.

How do I buy a domain? You don’t actually buy a domain, but actually rent it from whoever is managing the TLD you’re aiming for. Companies who manage Internet domains are called domain registrars. The most famous ones are Namecheap and Gandi.


The purpose of interconnecting all these computers is for them to interact with each other. And like humans talk in different languages, computers on the Internet talk using protocols.

Each of them serves a different purpose:

Protocol Used for Created in
FTP File transfer 1971
SMTP Sending Emails 1971
IMAP Receiving Emails 1986
IRC Chat 1988
HTTP Browsing HTML documents (Webpages) 1989


Now that we’ve seen how domains and protocols, we can build a URL: a Uniform Resource Locator.

For example, the current page’s URL is https://marksheet.io/internet.html, and can be divided in 3 parts:

  • https:// is the protocol
  • marksheet.io is the domain
  • /internet.html is the path

This URL is unique and defines

  • where to find something across the internet marksheet.io/internet.html
  • how the computer is supposed to read it https://

URLs can be more complex-looking. You can read about the anatomy of an URL.

A very large network of computers connected to each other.
A set of rules, like a language, in which computers communicate with each other.
IP address
A combination of numbers like which acts like a unique identifier for a computer connected to the Internet
A text like marksheet.io which acts like a unique identifier for a computer connected to the Internet. The difference with IP addresses is that domains are easier to read for humans.
  1. Apart from oceans obviously. 

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