Web-background information

Client and Server

A connection on the Internet takes place between 2 computers only:

one that has the information(the server)
one that wants it(the cient)

A client is a program that can take up many forms:a Web browser(like Firebox),an email client(like Outlook),amessengar app(like Whatsapp),a video streaming service(like Netflix)

Aserver can be considered a dedicated computer always connected to the Internet,whose sole purpose is to deliver content.

Clients will retrieve information from a server,where something is stored(a website,your emails,messages,movies).Although client programs also send information to server,they usually don't store it,while servers do.

Although any device connected to the Internet can be both a client and a server at the same time, most devices we use are considered clients, because we only retrieve data, and don’t deliver any.

IP Address

Like every house has a specific and unique postal address, each computer connected to the Internet is given an IP address, in order to be identified on the network.

An IP address usually looks like a combination of 4 numbers: 91.198.174.192.

Domains

Although IP addresses are useful for computers to tell each other apart thanks to their uniqueness, they are hard to read and remember for us humans.

That is why domains were created in 1985. They associate an IP address like 91.198.174.192 with a string of text like wikipedia.org. As a result, both are interchangeable: you can go to https://91.198.174.192 or https://wikipedia.org and end up on the exact same website.

A domain has 3 parts, that are read from right to left:

Top-Level Domain (or TLD): there are generic ones (.com, .org, .net) and country-specific ones (.us, .nl, .fr).
Domain name: a name like wikipedia or marksheet, that can include letters, numbers, but no space or dot.
Subdomain (optional). Although this 3rd part is optional, most websites use www as the default subdomain.

Think of domains as a way to name computers connected to the Internet.

How do I buy a domain? You don’t actually buy a domain, but actually rent it from whoever is managing the TLD you’re aiming for. Companies who manage Internet domains are called domain registrars. The most famous ones are Namecheap and Gandi.

Protocols

The purpose of interconnecting all these computers is for them to interact with each other. And like humans talk in different languages, computers on the Internet talk using protocols.

Each of them serves a different purpose:

Protocol	Used for	Created in
FTP	File transfer	1971
SMTP	Sending Emails	1971
IMAP	Receining Emails	1986
IRC	Chat	1988
HTTP	Browsing HTML documents(Webpages)	1989

If you want to know more here's a list of protocols.

URL

Now that we’ve seen how domains and protocols, we can build a URL: a Uniform Resource Locator.

For example, the current page’s URL is https://marksheet.io/internet.html, and can be divided in 3 parts:

https:// is the protocol
marksheet.io is the domain
/internet.html is the path

This URL is unique and defines

where to find something across the internet ：marksheet.io/internet.html
how the computer is supposed to read it : https://

URLs can be more complex-looking. You can read about the anatomy of an URL.

summary

Internet
A very large network of computers connected to each other.
Protocol
A set of rules, like a language, in which computers communicate with each other.
IP address
A combination of numbers like 91.198.174.192 which acts like a unique identifier for a computer connected to the Internet
Domain
A text like marksheet.io which acts like a unique identifier for a computer connected to the Internet. The difference with IP addresses is that domains are easier to read for humans.

ENGLISH

dedicated:adj.专门的
A client is a program that can take up many forms客户端是一个程序，可以有多种形式。
sole:adj唯一的，仅有的
retrieve:verb取回
domain:N-COUNT On the Internet, a domain is a set of addresses that shows, for example, the category or geographical area that an Internet address belongs to. (因特网上的)域
subdomain：子域。一个Internet域名的一部分，通常是一个网络、大学或公司
default：adj.默认的
The price rises will not be uniform across the country.全国各地的价格涨幅将不会划一。