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  2. Learn web development
  3. Getting started with the Web
  4. How the Web works

How the Web works

In This Article
  1. Clients and servers
  2. The other parts of the toolbox
  3. So what happens, exactly?
  4. DNS explained
  5. Packets explained
  6. See also
  7. Credit
Previous Overview: Getting started with the web

 

How the web works provides a simplified view of what happens when you view a webpage in a web browser on your computer or phone.

This theory is not essential to writing web code in the short term, but before long you'll really start to benefit from understanding what's happening in the background.

Clients and servers

Computers connected to the web are called clients and servers. A simplified diagram of how they interact might look like this:

  • Clients are the typical web user's internet-connected devices (for example, your computer connected to your Wi-Fi, or your phone connected to your mobile network) and web-accessing software available on those devices (usually a web browser like Firefox or Chrome).
  • Servers are computers that store webpages, sites, or apps. When a client device wants to access a webpage, a copy of the webpage is downloaded from the server onto the client machine to be displayed in the user's web browser.

The other parts of the toolbox

The client and server we've described above don't tell the whole story. There are many other parts involved, and we'll describe them below.

For now, let's imagine that the web is a road. On one end of the road is the client, which is like your house. On the other end of the road is the server, which is a shop you want to buy something from.

In addition to the client and the server, we also need to say hello to:

  • Your internet connection: Allows you to send and receive data on the web. It's basically like the street between your house and the shop.
  • TCP/IP: Transmission Control Protocol and Internet Protocol are communication protocols that define how data should travel across the web. This is like the transport mechanisms that let you place an order, go to the shop, and buy your goods. In our example, this is like a car or a bike (or however else you might get around).
  • DNS: Domain Name System Servers are like an address book for websites. When you type a web address in your browser, the browser looks at the DNS before retrieving the website. The browser needs to find out which server the website lives on, so it can send HTTP messages to the right place (see below). This is like looking up the address of the shop so you can access it.
  • HTTP: Hypertext Transfer Protocol is an application protocol that defines a language for clients and servers to speak to each other. This is like the language you use to order your goods.
  • Component files: A website is made up of many different files, which are like the different parts of the goods you buy from the shop. These files come in two main types:
    • Code files: Websites are built primarily from HTML, CSS, and JavaScript, though you'll meet other technologies a bit later.
    • Assets: This is a collective name for all the other stuff that makes up a website, such as images, music, video, Word documents, and PDFs.

So what happens, exactly?

When you type a web address into your browser (for our analogy that's like walking to the shop):

  1. The browser goes to the DNS server, and finds the real address of the server that the website lives on (you find the address of the shop).
  2. The browser sends an HTTP request message to the server, asking it to send a copy of the website to the client (you go to the shop and order your goods). This message, and all other data sent between the client and the server, is sent across your internet connection using TCP/IP.
  3. Provided the server approves the client's request, the server sends the client a "200 OK" message, which means "Of course you can look at that website! Here it is", and then starts sending the website's files to the browser as a series of small chunks called data packets (the shop gives you your goods, and you bring them back to your house).
  4. The browser assembles the small chunks into a complete website and displays it to you (the goods arrive at your door — new shiny stuff, awesome!).

DNS explained

Real web addresses aren't the nice, memorable strings you type into your address bar to find your favorite websites. They are special numbers that look like this: 63.245.217.105.

This is called an IP address, and it represents a unique location on the Web. However, it's not very easy to remember, is it? That's why Domain Name Servers were invented. These are special servers that match up a web address you type into your browser (like "mozilla.org") to the website's real (IP) address.

Websites can be reached directly via their IP addresses. Try going to the Mozilla website by typing 63.245.217.105 into the address bar on a new browser tab.

A domain name is just another form of an IP address

Packets explained

Earlier we used the term "packets" to describe the format in which the data is sent from server to client. What do we mean here? Basically, when data is sent across the web, it is sent as thousands of small chunks, so that many different web users can download the same website at the same time. If web sites were sent as single big chunks, only one user could download one at a time, which obviously would make the web very inefficient and not much fun to use.

See also

  • How the Internet works
  • HTTP — an Application-Level Protocol
  • HTTP: Let’s GET It On!
  • HTTP: Response Codes

Credit

Street photo: Street composing, by Kevin D.

Previous Overview: Getting started with the web

 

Document Tags and Contributors

Tags: 
  • Beginner
  • Client
  • DNS
  • HTTP
  • Infrastructure
  • IP
  • l10n:priority
  • Learn
  • Server
  • TCP
 Contributors to this page: chrisdavidmills, hadleyel, bunnybooboo, AlexanderJohn, CommonSnowFlake, Jeremie, corderophilosophy, klez, SphinxKnight, marlon7, diogeneshamilton, xfq, Andrew_Pfeiffer
 Last updated by: chrisdavidmills, Jul 17, 2017, 4:18:51 AM
See also
  1. Complete beginners start here!
  2. Getting started with the Web
    1. Getting started with the Web overview
    2. Installing basic software
    3. What will your website look like?
    4. Dealing with files
    5. HTML basics
    6. CSS basics
    7. JavaScript basics
    8. Publishing your website
    9. How the Web works
  3. HTML — Structuring the Web
  4. Introduction to HTML
    1. Introduction to HTML overview
    2. Getting started with HTML
    3. What's in the head? Metadata in HTML
    4. HTML text fundamentals
    5. Creating hyperlinks
    6. Advanced text formatting
    7. Document and website structure
    8. Debugging HTML
    9. Assessment: Marking up a letter
    10. Assessment: Structuring a page of content
  5. Multimedia and embedding
    1. Multimedia and embedding overview
    2. Images in HTML
    3. Video and audio content
    4. From object to iframe — other embedding technologies
    5. Adding vector graphics to the Web
    6. Responsive images
    7. Assessment: Mozilla splash page
  6. HTML tables
    1. HTML tables overview
    2. HTML table basics
    3. HTML Table advanced features and accessibility
    4. Assessment: Structuring planet data
  7. CSS — Styling the Web
  8. Introduction to CSS
    1. Introduction to CSS overview
    2. How CSS works
    3. CSS syntax
    4. Selectors introduction
    5. Simple selectors
    6. Attribute selectors
    7. Pseudo-classes and pseudo-elements
    8. Combinators and multiple selectors
    9. CSS values and units
    10. Cascade and inheritance
    11. The box model
    12. Debugging CSS
    13. Assessment: Fundamental CSS comprehension
  9. Styling text
    1. Styling text overview
    2. Fundamental text and font styling
    3. Styling lists
    4. Styling links
    5. Web fonts
    6. Assessment: Typesetting a community school homepage
  10. Styling boxes
    1. Styling boxes overview
    2. Box model recap
    3. Backgrounds
    4. Borders
    5. Styling tables
    6. Advanced box effects
    7. Assessment: Creating fancy letterheaded paper
    8. Assessment: A cool-looking box
  11. CSS layout
    1. CSS layout overview
    2. Introduction
    3. Floats
    4. Positioning
    5. Practical positioning examples
    6. Flexbox
    7. Grids
  12. JavaScript — Dynamic client-side scripting
  13. JavaScript first steps
    1. JavaScript first steps overview
    2. What is JavaScript?
    3. A first splash into JavaScript
    4. What went wrong? Troubleshooting JavaScript
    5. Storing the information you need — Variables
    6. Basic in JavaScript — Numbers and operators
    7. Handling text — Strings in JavaScript
    8. Useful string methods
    9. Arrays
    10. Assessment: Silly story generator
  14. JavaScript building blocks
    1. JavaScript building blocks overview
    2. Making decisions in your code — Conditionals
    3. Looping code
    4. Functions — Reusable blocks of code
    5. Build your own function
    6. Function return values
    7. Introduction to events
    8. Assessment: Image gallery
  15. Introducing JavaScript objects
    1. Introducing JavaScript objects overview
    2. Object basics
    3. Object-oriented JavaScript for beginners
    4. Object prototypes
    5. Inheritance in JavaScript
    6. Working with JSON data
    7. Object building practise
    8. Assessment: Adding features to our bouncing balls demo
  16. Accessibility — Make the web usable by everyone
  17. Accessibility guides
    1. Accessibility overview
    2. What is accessibility?
    3. HTML: A good basis for accessibility
    4. CSS and JavaScript accessibility best practices
    5. WAI-ARIA basics
    6. Accessible multimedia
    7. Mobile accessibility
  18. Accessibility assessment
    1. Assessment: Accessibility troubleshooting
  19. Tools and testing
  20. Cross browser testing
    1. Cross browser testing overview
    2. Introduction to cross browser testing
    3. Strategies for carrying out testing
    4. Handling common HTML and CSS problems
    5. Handling common JavaScript problems
    6. Handling common accessibility problems
    7. Implementing feature detection
    8. Introduction to automated testing
    9. Setting up your own test automation environment
  21. Server-side website programming
  22. First steps
    1. First steps overview
    2. Introduction to the server-side
    3. Client-Server overview
    4. Server-side web frameworks
    5. Website security
  23. Django web framework (Python)
    1. Django web framework (Python) overview
    2. Introduction
    3. Setting up a development environment
    4. Tutorial: The Local Library website
    5. Tutorial Part 2: Creating a skeleton website
    6. Tutorial Part 3: Using models
    7. Tutorial Part 4: Django admin site
    8. Tutorial Part 5: Creating our home page
    9. Tutorial Part 6: Generic list and detail views
    10. Tutorial Part 7: Sessions framework
    11. Tutorial Part 8: User authentication and permissions
    12. Tutorial Part 9: Working with forms
    13. Tutorial Part 10: Testing a Django web application
    14. Tutorial Part 11: Deploying Django to production
    15. Web application security
    16. Assessment: DIY mini blog
  24. Express Web Framework (node.js/JavaScript)
    1. Express Web Framework (Node.js/JavaScript) overview
    2. Express/Node introduction
    3. Setting up a Node (Express) development environment
    4. Express tutorial: The Local Library website
    5. Express Tutorial Part 2: Creating a skeleton website
    6. Express Tutorial Part 3: Using a database (with Mongoose)
    7. Express Tutorial Part 4: Routes and controllers
    8. Express Tutorial Part 5: Displaying library data
    9. Express Tutorial Part 6: Working with forms
    10. Express Tutorial Part 7: Deploying to production
  25. Further resources
  26. Advanced learning material
    1. WebGL: Graphics processing
  27. Common questions
    1. HTML questions
    2. CSS questions
    3. JavaScript questions
    4. How the Web works
    5. Tools and setup
    6. Design and accessibility
  28. How to contribute