Web Server

A web server is a computer with a boot device or other disk containing a web site. The term may also refer to an application that helps a computer to perform web server functions.

If one site runs more than one server they must use different port numbers. Alternatively, several hostnames may be mapped to the same computer in which case they are known as "virtual servers".

Apache, IIS, and nginx are three popular web servers. There are many others including some for practically every platform. Servers differ mostly in the "server-side" features they offer such as server-side includes, and in their authentication and access control mechanisms. All decent servers support CGI and most have some binary API as well.

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Learn more about web servers 
How Web Server Work?
Name Servers

List of Web Servers
Apache
IIS
Jigsaw
Lightttpd

Web Server Quiz