At the base of the client-server, contains the pages and resources that make up the World Wide Web
Even if someone imagines a future where you can live without it, now the infrastructure and the very functioning of the Internet makes total reliance on web servers. Designed in the late '60s and early' 70s (more or less coinciding with the early development of ARPANET) but actually implemented only in the early 90s with Tim Berners-Lee and his project of the World Wide Web, the client-server model is the basis on which rests the web and allows you to access all the content of the Net: from images to video, from HTML pages to the application.
At the center of this architecture are precisely the web server, which plays at the same time, the function of the container (web pages, multimedia material, programs and more) and performer (instruction coming from clients or from other servers).
What is
The primary function of a server is to conserve, "process" and "deliver" web pages to clients who request it. The communication between the parties (the web server and the web client) occurs through HTTP (HyperText Transfer Protocol) and concerns, in most cases, HTML pages (containing text, images, style sheets and scripts). A user agent (usually a browser, but can also be a web crawler) begins a "conversation" with the server by sending a request for a specific resource, and the server responds with the requested content or an error message if the resource is absent, is no longer available or anyway not longer present. The resource is typically a file hosted on secondary storage server itself.
Many web servers also use the so-called server-side scripting (server-side scripting) using Active Server Pages (ASP), PHP and other scripting languages that allow you to "change" the behavior and operation of the server on-the-fly (literally "on the fly") without altering the basic structure of the server itself. In this way the server can provide both static web pages is to create dynamic web pages "fishing" content and composing them into a single framework HTML.
Before you can get to the HTML page or any other content on the web, the client is "forced" to a lengthy process of requests and responses made by the use of different communication protocols. The requests go through a web browser and are "sorted" the web thanks to the URL (Uniform Resource Locator), the web addresses that uniquely identify each resource present in the server. A URL is broken down into three parts: the protocol used in the communication between the two known (usually HTTP, but may also be the HTTPS or FTP), the server name or the domain that hosts the resource ("www.fastweb.it" for example) and the name of the given "target" (for example, the URL https://it.wikipedia.org/wiki/Informatica identifies the web page on the definition of "Information" within the domain wikipedia, via HTTPS).
All resources on the web are identified by a unique numerical address (IP address) composed in different ways depending on the protocol (IPv4 or IPv6) and corresponding to the alphanumeric URL. So that the web browser can find the corresponding server, you must have a name server (basic element of the Domain Name System or DNS) "translates" the URL into an IP address and individuals consequently the resource "target" (for example, it.wikipedia.org the URL matches the IPv4 91,198,174,192 and is equivalent to it).
Identified the IP address and the server containing the desired resource, comes in the HTTP protocol: the browser sends a GET request (from the verb get, translated as "get", "receive") to the web server responds by sending the code HTML page or resource sought. The browser reads the HTML tags included in the received code in response, format the page as well as indications transposed and displays it on the screen.
