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**The Open Web**
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## World Wide Web
Tim Berners-Lee—*1990*
Invented at CERN for research documents
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- Originally the Web was made so scientists could easily share their research
- *It was made for just text*
- It has changed much since then with lots of new features and media abilities
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## Specialized computers
- Web servers—*just serve websites*
- Chat servers
- File servers
- *etc.*
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- The web is really just a whole bunch of computers that are connected together
- *And they all magically know how to speak the same languages*
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## Connected computers
Each with a unique name—the IP Address
- 127.0.0.1
- 2001:0db8:85a3:0000:0000:8a2e:0370:7334
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- The IP address is the unique name that computers use to address each other
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## IPs are for computers
*IP addresses are confusing for humans*
Domains, like `github.com`, are for us
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## DNS
(Domain Name System)
### Maps Domains ⬌ IPs
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- The DNS is the way computers will take the human-friendly domain and convert it into a computer friendly IP address
- It’s a system to computers that have huge lists of Domain-To-IP conversions
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dns-1.svg |
Everything starts in your browser, on your computer…
1. You type in a domain you’d like to reach, like `google.ca`
2. Your computer has no idea what `google.ca` is or where to find the computer that is `google.ca`
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dns-2.svg |
But your computer does know how to contact the DNS…
1. Your computer sends a message to the DNS and says, “Hey DNS, I’m looking for ‘google.ca’ can you tell me where that is?”
2. The DNS responds one of two ways:
- “Yes, the IP address is 8.8.8.4”
- or “No, try this other DNS that might know about ‘google.ca’; its IP address is 4.4.4.2”
All of this usually happens really quickly, we’re talking milliseconds here. Your computer even keeps a cache/history of all the domain-to-IP mappings so it doesn’t have to look them up in the future
And all the DNS computers regularly synchronize themselves all over the world
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dns-3.svg |
Now that your computer knows the IP address of the computer ‘google.ca’ is on it contacts that computer directly:
- “Hey 8.8.8.4, I’m looking for ‘google.ca’, do you have it?”
- “Yep, I have ‘google.ca’, here’s the `index.html` file you’ll need”
- or maybe even, “Nope, I don’t have ‘google.ca’, but this computer over here does
After your computer starts downloading the `index.html` file a whole series of other things start to happen…
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## Websites are lots and lots of files…
- HTML
- CSS
- JavaScript
- Images
- Video
*Each downloaded separately*
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Websites are just code (except for images & video)
As your browser reads the HTML code it finds that it needs other code, like CSS or JavaScript or other files like images and videos
*Each of these things are downloaded to your computer separately*
And often saved in the cache so they don’t need to be downloaded the next time you visit the website
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## Performance matters
The more files the slower your website
*Performance is the most important design constraint*
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