Year 11 · Computer Science · Autumn 2
The internet and its uses · Lesson 2 of 5
DNS, cookies, digital currency and blockchain
Unplugged5.1 The internet and the World Wide Web5.2 Digital currency
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
You will learn to
- Describe the role of DNS when a user types a URL.
- Explain the difference between session cookies and persistent cookies, with a use of each.
- Explain what digital currency is.
- Describe how a blockchain records transactions, and why a change to one block is noticed.
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
Success criteria
You have got it when you can say:
- I can explain DNS using the phone book example.
- I can say whether a cookie is session or persistent from what it does.
- I can explain why changing an old block breaks the chain, using our paper blockchain.
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
Retrieval starter
Questions from before. Write your answers, then show them.
- Last lesson
Pharming is…
A Guessing every passwordB Being sent to a fake website even when you type the right addressC A fake email asking for a password
B. Being sent to a fake website even when you type the right address
- Last unit
Which of these is system software?
A A gameB A word processorC The operating system
C. The operating system
- Last year
FOR i ← 1 TO 10 … NEXT i runs the loop…
A 9 timesB 11 timesC 10 times
C. 10 times
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
Key words (1 of 4)
- Internet
- The worldwide network of connected computer networks: the physical infrastructure.
- World Wide Web (WWW)
- The collection of websites and web pages that are reached using the internet.
- URL
- Uniform resource locator: the text address of a web page, made of protocol, domain name and file name.
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
Key words (2 of 4)
- HTTP / HTTPS
- The rules for sending web pages; HTTPS adds encryption using SSL.
- Web browser
- Application software that fetches web pages and renders HTML so you can see them.
- DNS
- Domain Name System: servers that find the IP address that matches a domain name.
- IP address
- A number that identifies a device on a network, such as 151.101.0.81.
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
Key words (3 of 4)
- Cookie
- A small text file a website stores on your device to remember you.
- Digital currency
- Money that exists only electronically.
- Blockchain
- A time-stamped digital ledger of transactions, stored as linked blocks on many computers, that cannot be altered without detection.
- Hash
- A fixed-length code calculated from data; any change to the data changes the hash.
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
Key words (4 of 4)
- SSL
- Secure Sockets Layer: a protocol that uses certificates and encryption to secure data between browser and server.
5.1 The internet and the World Wide Web · The explanation · step 1 of 10 · part 1 of 3
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.
5.1 The internet and the World Wide Web · The explanation · step 1 of 10 · part 2 of 3
The internet is not the same as the web (continued)
| Internet | World Wide Web | |
|---|---|---|
| What it is | A global network of networks (hardware and connections) | A collection of web pages and websites (information) |
| Made of | Cables, routers, servers, wireless links | Pages written in HTML, linked by hyperlinks |
| Uses | Web, email, video calls, file transfer, online games | Viewing web pages in a browser |
| Protocols | TCP/IP and many others | HTTP and HTTPS |
5.1 The internet and the World Wide Web · The explanation · step 1 of 10 · part 3 of 3
The internet is not the same as the web (continued)
Do not use the two words as if they mean the same thing. The internet is the network. The web is the pages.
5.1 The internet and the World Wide Web · The explanation · step 2 of 10 · part 1 of 4
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.
5.1 The internet and the World Wide Web · The explanation · step 2 of 10 · part 2 of 4
The parts of a URL (continued)
| Part of the domain | Meaning |
|---|---|
| www | This is a web server |
| bbc | The organisation's name |
| .co.uk | Top-level part: a company in the UK (others: .com, .org, .es, .gov) |
5.1 The internet and the World Wide Web · The explanation · step 2 of 10 · part 3 of 4
The parts of a URL (continued)
5.1 The internet and the World Wide Web · The explanation · step 2 of 10 · part 4 of 4
The parts of a URL (continued)
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.
The 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.
5.1 The internet and the World Wide Web · The explanation · step 3 of 10 · part 1 of 2
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.
5.1 The internet and the World Wide Web · The explanation · step 3 of 10 · part 2 of 2
HTTP and HTTPS (continued)
With plain HTTP, data travels as readable text. Someone on the same public Wi-Fi could read your password. HTTPS stops this.
HTTPS means the connection is encrypted. It does not prove the website is honest. A fake website can also use HTTPS.
5.1 The internet and the World Wide Web · The explanation · step 4 of 10 · part 1 of 2
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.
5.1 The internet and the World Wide Web · The explanation · step 4 of 10 · part 2 of 2
What a web browser does (continued)
| Browser function | What it does |
|---|---|
| Renders HTML | Turns HTML code into a visible web page |
| Bookmarks / favourites | Saves the URL of a page so you can go back to it in one click |
| History | Keeps a list of pages you have visited, with dates and times |
| Tabs | Lets you open several pages in one browser window |
| Cookies | Stores small files from websites on your device |
| Navigation tools | Back, forward, refresh/reload and home buttons; clickable hyperlinks |
| Address bar | Where you type or see the URL; often also works as a search box |
The explanation · 6 more steps
More on the lesson page
The lesson page has the rest of the explanation, step by step:
- How a web page is retrieved, step by step
- Cookies: session and persistent
- What cookies are used for
- What digital currency is
- Blockchain: a chain of linked blocks
- Why a blockchain cannot be altered
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
Quick quiz · 1 of 3
Each block in a blockchain contains…
- A A hash of the previous block, so any change shows
- B Only a password
- C A picture
A. A hash of the previous block, so any change shows
Change one block and every hash after it stops matching.
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
Quick quiz · 2 of 3
A proxy server…
- A Is the same as a router
- B Stores the DNS
- C Sits between users and the internet, filtering and caching
C. Sits between users and the internet, filtering and caching
It can block sites, hide the user's address and keep copies of popular pages.
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
Quick quiz · 3 of 3
The World Wide Web is…
- A The cables and routers
- B The same thing as the internet
- C Pages that use the internet via HTTP
C. Pages that use the internet via HTTP
The internet is the network. The web is one service on it.
Year 11 · Computer Science · The internet and its uses · Lesson 2 of 5
Exit ticket
Answer on paper before you go. Then check.
DNS…
A Turns a domain name into an IP addressB Encrypts the pageC Stores cookies
A. Turns a domain name into an IP address The phone book of the internet.
A session cookie…
A Lasts for yearsB Is deleted when the browser closesC Is a type of virus
B. Is deleted when the browser closes A persistent cookie stays. A session cookie goes with the session.