The internet is not the same as the web
The internet is the physical network. It is millions of computers, cables, routers and wireless links joined together across the world. It is the infrastructure.
The World Wide Web (WWW) is a collection of websites and web pages stored on computers connected to the internet.
The web is one service that uses the internet. Email, online gaming and video calls also use the internet, but they are not the web.
e.g.ExampleThink of the Madrid Metro. The tunnels, tracks and stations are the internet. The trains carrying people to places are like services. The web is one line on that network; email is another.
!Watch outDo not use the two words as if they mean the same thing. The internet is the network. The web is the pages.
The parts of a URL
A URL (uniform resource locator) is the text address of a web page. It is what you type into the address bar.
Cambridge splits a URL into three parts: the protocol, the domain name and the web page/file name.
The protocol is the set of rules used to transfer the page, such as `https`. The domain name names the web server, such as `www.bbc.co.uk`. The web page/file name is the exact page or file on that server, often with a folder path before it.
e.g.Examplehttps://www.bbc.co.uk/news/technology.html
Protocol: https
Domain name: www.bbc.co.uk
Path (folder): /news/
Web page/file name: technology.html
Try it in the toy: type this URL to see its parts. Then press Step to follow the DNS lookup and the request.
?Why?People remember names far more easily than numbers. The URL is a human-friendly label; DNS later turns the domain name into the server's IP address.
!Watch outThe protocol is not "www". The protocol is the part before `://`, such as `http` or `https`.
There is something to try for this step in the IGCSE library.
HTTP and HTTPS
HTTP (Hypertext Transfer Protocol) is the set of rules for sending web pages between a web server and a browser.
HTTPS (Hypertext Transfer Protocol Secure) is HTTP with encryption added, using SSL/TLS. Encryption scrambles the data so that anyone who intercepts it cannot read it.
A browser shows a padlock in the address bar when HTTPS is used. You should only type passwords or card numbers on HTTPS pages.
?Why?With plain HTTP, data travels as readable text. Someone on the same public Wi-Fi could read your password. HTTPS stops this.
!Watch outHTTPS means the connection is encrypted. It does not prove the website is honest. A fake website can also use HTTPS.
What a web browser does
A web browser is application software that lets you find, fetch and view web pages. Examples are Chrome, Firefox, Safari and Edge.
Its main job is to render HTML: it reads the HTML code from the server and turns it into the page you see, with text, images and links.
Cambridge lists these other functions. Learn each one.
How a web page is retrieved, step by step
Every web server has an IP address, a number that identifies it on the internet, such as `151.101.0.81`. Computers need this number to send data to each other.
People type a domain name, not a number. The Domain Name System (DNS) is a system of servers that look up the IP address for a domain name. It works like a phone book for the internet.
Follow the numbered arrows in the diagram, then read the steps.
e.g.ExampleYou type www.bbc.co.uk/news into the address bar.
1. The browser sends the domain name www.bbc.co.uk to a DNS server.
2. The DNS server looks up the matching IP address. If it does not know it, it asks another DNS server.
3. The DNS server sends the IP address back to the browser.
4. The browser sends an HTTP(S) request to the web server at that IP address, asking for the page.
5. The web server sends back the page's HTML (and files such as images).
6. The browser renders the HTML and shows the page.
?Why?Splitting the job lets humans use names and computers use numbers. DNS servers also store recent lookups, so popular sites are found faster.
!Watch outThe DNS server does not send the web page. It only sends the IP address. The page comes from the web server.
There is a diagram for this step in the IGCSE library.
Cookies: session and persistent
A cookie is a small text file that a website stores on the user's device. The next time the browser visits that site, it sends the cookie back, so the site recognises the user.
A session cookie is temporary. It is kept in memory and deleted when the browser is closed.
A persistent cookie is saved on the device's storage. It stays until its expiry date or until the user deletes it. It remembers you between visits.
What cookies are used for
Cambridge lists four main uses of cookies.
Saving personal details, such as your name and delivery address, so you do not retype them.
Tracking user preferences, such as language, dark mode or the pages you look at, so the site can be personalised and show targeted adverts.
Holding items in an online shopping cart while you keep browsing.
Storing login details, so you stay logged in when you return.
e.g.ExampleOn a supermarket website you add milk and bread to the cart, then go to another page. A session cookie keeps the cart full. Next week the site greets you by name and shows Spanish prices: that is a persistent cookie.
!Watch outCookies are not programs and cannot run code. They are data. The privacy worry is that persistent cookies can track your browsing, which is why sites must ask your permission in Spain and the UK.