How a Web Page Is Loaded — World Wide Web | IGCSE Computer Science

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 3% of your exam marks.

stable

Rare

Stable3%

The difference between the internet and the WWW, and cookie/browser functions, are typical questions.

Putting the pieces together, here is the full journey from typing a URL to seeing the page:

The user enters a in the browser's address bar (or clicks a link that contains one).
The browser strips out the domain name from the URL.
The browser asks a server to translate the domain name into the IP address of the web server hosting that site.
The browser sends an HTTP/ request to that IP address, asking for the resource at the URL's file path.
The receives the request, finds the requested resource, and sends back an HTTP/HTTPS response.
The response contains the document for the page, plus references to any , JavaScript, images and other media the page needs.
The browser renders the HTML (with CSS to style it and JavaScript to make it interactive) into the visible web page.
Any extra files referenced (images, scripts) trigger their own HTTP requests, which the browser fires off in parallel.
The user sees the finished page and can interact with it (click links, fill in forms, etc.).

The Domain Name System (DNS)

The DNS (Domain Name System) is the 's directory service, mapping human-readable domain names to numerical IP addresses.

Think of DNS as a global phonebook. When the browser needs to know where www.example.com is, it asks a DNS server. The DNS server looks up the domain in its records and replies with the IP address. The browser can now connect directly to the server at that address.

DNS is what makes URLs usable: without it, every user would have to remember IP addresses. DNS is hierarchical (root servers, top-level domains like .com, .org, individual sites), but the simple "domain name → IP address" mapping is enough at this level.

The web server

A web server is a computer (or set of computers) whose job is to store web pages and respond to browser requests for them. Typical web-server features:

Available 24/7 so people anywhere in the world can reach the site at any time.
Serves the same page to many users at once (sometimes thousands or millions).
Maintained by the website's owner (or a hosting company); responsible for keeping it patched, backed up and secure.

Big websites use many web servers behind a load balancer to share the traffic; small websites may live on a single shared server with many other sites.

HTML: the language of web pages

HTML (Hypertext Markup Language) is the markup language used to define the structure and content of a web page.

HTML is made up of tags that wrap content:

<p>This is a paragraph.</p>: a paragraph
<h1>Welcome</h1>: a top-level heading
<a href="...">Click here</a>: a hyperlink
<img src="..." alt="...">: an embedded image
<ul> and <li>: bullet lists

A complete simple HTML page might look like:

<!DOCTYPE html>
<html>
  <head>
    <title>My Web Page</title>
  </head>
  <body>
    <h1>Welcome to my site</h1>
    <p>This is a paragraph of text.</p>
  </body>
</html>

The browser reads this HTML and produces the visible page. Two related technologies usually accompany HTML:

CSS (Cascading Style Sheets) controls the visual style of the page (colours, fonts, layout).
JavaScript is a programming language that runs inside the browser and makes pages interactive (form validation, animations, live updates, games).

The exam wants you to know that HTML provides structure and content, CSS provides styling, and JavaScript provides interactivity, but does not require you to write any of them in detail.

Exam tip

Define HTML / its role

What comes up: name the language whose tags include <head> and <body>, or state what HTML is used for.

Watch out: HTML defines the structure/content of a web page using tags; it does not "display" the page — the browser renders/displays it. That structure-vs-display distinction is the credited point.

Exam tip

State how SSL/HTTPS secures data in transit

What comes up: A 1–2 mark question asking how the SSL protocol (or HTTPS) keeps data secure when it is sent over the internet.

Write (two marks): (1) SSL encrypts the data before it is sent. (2) If the data is intercepted during transmission it is unreadable to the attacker (because they do not have the decryption key). A 1-mark version: "It encrypts the data."

Watch out: Saying "it stops data being intercepted" is not credited — the data can still be intercepted, but encryption makes it meaningless. The mark is for the word encrypted/encryption.