The internet and the world wide web

Computer Science · The internet and its uses. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

The internet is the infrastructure: a huge network of networks joined by cables, routers and other hardware. The world wide web is the collection of web pages and websites that are accessed using the internet. They are not the same thing.

Each web page has a URL (uniform resource locator), a text-based address that is easy for people to use. A web browser is software that requests web pages and renders the HTML so the page is displayed.

Computers find each other with IP addresses, not names. A domain name server (DNS) finds the IP address that matches a domain name. Websites can also store small files called cookies on the user's device.

Rules to remember

A URL has a protocol, a domain name and a web page or file name. In https://www.myschool.org/exams/dates.html these are https, www.myschool.org and /exams/dates.html.
HTTP (hypertext transfer protocol) is the set of rules for sending web pages between a web server and a browser.
HTTPS is the secure version: the data sent between the browser and the web server is encrypted.
Browser functions: rendering HTML, address bar, navigation tools, bookmarks and favourites, user history, multiple tabs, storing cookies.
Retrieving a page: browser sends the domain name to the DNS → DNS returns the IP address → browser sends a request to the web server at that address → server sends the HTML → browser renders it.
Cookies are small text files sent by a web server and stored by the browser. They save personal details, login details, preferences and items in a shopping basket.
A session cookie is deleted when the browser is closed. A persistent cookie stays on the device until it expires or the user deletes it.

Common mistake

Students often say the DNS sends the web page. The DNS only returns the IP address; the web server sends the HTML and the browser renders it.

Worked example

An online shop keeps the items in a user's basket while they move from page to page. When the user closes the browser and opens it again, the basket is empty. Which type of cookie was used?

The basket was remembered between pages, so the data was held in a cookie.
The data was lost as soon as the browser was closed.
A persistent cookie would still be on the device after the browser is closed, so it is not that type.

Answer: A session cookie.

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