The internet
A network of networks
The internet is a worldwide collection of computer networks, all connected together. Your home network, your school's network and the networks of businesses and governments all join it, through routers and the cables of telecoms companies.
The internet carries many services, such as email, video calls and streaming. The World Wide Web, the collection of web pages you visit in a browser, is just one of them.
A server is a computer that provides a service; a client requests and uses it:
| Server | Service it provides |
|---|---|
| Web server | Stores web pages and sends them to the browsers that ask for them |
| File server | Stores files, and lets users save and fetch them |
| Email server | Stores, sends and receives email |
Key terms
DNS: finding a website
You visit websites by their URL, such as www.example.com, but computers find each other by IP address, such as 203.0.113.5. The DNS (Domain Name Service) turns one into the other. It's made up of many Domain Name Servers around the world.
- You type a URL into your browser.
- The browser sends the domain name to a DNS server, asking for its IP address.
- The DNS server looks the name up. If it doesn't know it, it asks other DNS servers.
- It sends the IP address back to the browser, or an error if the name doesn't exist.
- The browser uses the IP address to request the page from the web server.
- The web server sends the page back, and the browser shows it.
Without DNS, you'd have to remember the IP address of every website.
Key terms
Hosting
Hosting is storing a website, or other files and services, on a server connected to the internet all the time, so others can reach them.
Most people and businesses don't run their own web servers. Instead, they pay a hosting company, which keeps their website on its servers, keeps them running day and night, and deals with the hardware, the electricity and the security.
Key terms
The cloud
The cloud means services provided remotely, over the internet, on servers owned by someone else: storing files, running software in a browser, or renting processing power.
| Advantages | Disadvantages |
|---|---|
| Use your files and software anywhere, on any device | Needs an internet connection; slow or no connection means slow or no access |
| Easy to share and work on files together | You depend on the provider: if its servers go down, or it closes, you lose access |
| No hardware to buy or maintain; the provider does the backups and updates | Often an ongoing cost, such as a monthly subscription |
| Easy to get more storage as you need it | Your data is held by someone else, perhaps in another country, so you have less control over its security and privacy |
Exam tip
For advantages and disadvantages, explain each point, and link it to the scenario.