When the Internet user views the web page, he requests this page on the Web server. If the website address is entered into a line of the browser, then the browser makes request at the Web server for the web page, and the server sends data on her to the user's computer.
Instruction
1. The word "server" - English-speaking origin, it literally means "the servicing device". In the sphere of computer science the server is responsible for providing information to network resources.
2. When on the Web server the website is created, the IP address is assigned to it. IP – the abbreviation meaning "Internet protocol". The IP address consists of ten digits with points (for example, 127.21.61.137). To make request at the Web server for any given website, the browser on the computer at first should learn the IP address of this website. If this information is not in a browser cache, then it makes the corresponding request at the DNS server online.
3. Then the DNS server reports to the browser to what IP address this website is located. After that the browser requests the Website URL address from the Web server. The server responds, sending the required page. If this page does not exist, the server sends the error message. The browser receives the message and displays it.
4. In the professional sphere in such situation the browser is called "client", and the Web server - "server". Also these concepts belong to computers. Those computers which act as Web servers are called servers, and those which are connected to the Internet to obtain information – clients.
5. The Web server usually contains information on more than one website. Many hosting companies provide the place to hundreds and even thousands to websites on one Web server. The unique IP address is usually attributed to each website. This address is decrypted by the DNS server for the purpose of receiving a domain name.
6. Domain names exist for the reason that it is difficult to most of Internet users to remember ten-digit numbers which the IP addresses are. Besides, these addresses sometimes change.
7. Each server computer provides access to information which is stored on it, using the numbered ports. Each service (e-mail, a hosting) provided by the server has the certain port. Clients are connected to service through the IP address and through port.
8. When the client unites to the server through port, it uses the protocol. The protocol represents the text showing how the client and the server will interact.
9. Each Web server will be coordinated with the HTTP protocol. The most elementary form of interaction understood by the HTTP server contains only one command: "Receive". Originally the protocol was limited to the fact that the server sent to the client the required file and was switched-off. Later the protocol was improved, and all URL began to be sent to the client.
10. When the user prints the name of the link URL in a line of the browser, the browser breaks the name into three parts: protocol, name of the server, name of the file. The browser obtains information on the website IP address through the name of the server, and with its help is connected to a server computer. Then the browser connects to the Web server to this IP address through port. Following the protocol, the browser sends to the server the Receive command. The server sends the text in the HTML format to the web page. The browser reads out HTML - tags and formats the page for the computer client screen.
11. The majority of Web servers resort to security measures. For example, they can limit an information access the password and the login. More advanced servers raise the security level, protecting a resource encryption of information between the client and the server that personal information (the credit card number, the phone number) remained unavailable to other users. All aforesaid belongs to so-called static pages, that is it which remain invariable until the creator corrects them.
12. But there are also dynamic pages. On them any user can make search by a keyword, make entries in guest books, comment. In that case the Web server processes information and generates the new page. In most cases at the same time CGI scripts – the special commands allowing to alter the web page are used.