Web servers - Web server

The term web server can mean one of two things:

1. a computer responsible for serving web pages, mostly HTML documents, via the HTTP protocol to clients, mostly web browsers;
2. a software program that is working as a daemon serving web documents.

Connections to HTTP servers are made using web browsers.

Common features

Although web server programs differ in detail, they all share some basic common features. Every web server program operates by accepting HTTP requests from the network, and providing an HTTP response to the requester. The HTTP response typically consists of an HTML document, but can also be a raw text file, an image, or some other type of document.

Path translation

Web servers translate the path component of a URI into a local file system resource. The URI path specified by the client is relative to the web server's root directory. Consider the following URI as it would be requested by a client:

http://www.example.com/path/file.html

The client's web browser will translate it into a connection to www.example.com with the following HTTP 1.1 request:

GET /path/file.html HTTP/1.1
Host: www.example.com

The web server on www.example.com will append to its root path, which on a UNIX machine would commonly be /var/www/htdocs. The result will be the local file system resource:

/var/www/htdocs/path/file.html

The web server will then read the file, if it exists, and send a response to the client's web browser. The request will contain any appropriate headers and the file itself.

Historical note

In 1989 Tim Berners-Lee proposed to his employer CERN (European center for nuclear research) a new project, which had the goal of easing the exchange of information between scientists by using a hypertext system. As a result of the implementation of this project, Berners-Lee wrote two programs: a browser called WorldWideWeb and the world's first web server, which ran on NeXTSTEP. Today, this machine can be inspected in the visitor center of CERN in the Microcosm exhibition. See also: A picture of the first webserver.

Software

The most common web or HTTP server programs are:

* Apache HTTP Server from the Apache Software Foundation.
* Internet Information Services (IIS) from Microsoft.
* Sun Java Web Server from Sun Microsystems, formerly Sun ONE (originally Netscape's iPlanet, née Enterprise).
* Zeus Web Server from Zeus Technology.

Apache is by far the most common software, with over 69% market share according to the June 2005 Netcraft Web Server Survey