A web server is a computer program that delivers (serves) content, such as this web page, using the Hypertext Transfer Protocol. The term web server can also refer to the computer or virtual machine running the program.

The primary function of a web server is to deliver web pages (HTML documents) and associated content (e.g. images, style sheets, JavaScripts) to clients. A client, commonly a web browser or web crawler, makes a request for a specific resource using HTTP and, if all goes well, the server responds with the content of that resource.

The resource is typically a real file on the server's secondary memory, but this is not necessarily the case and depends on how the web server is implemented. While the primary function is to serve content, a full implementation of HTTP also includes a way of receiving content from clients. This feature is used for submitting web forms, including uploading of files. Many generic web servers also support server-side scripting (e.g. Apache HTTP Server and PHP).

This means that the behaviour of the web server can be scripted in separate files, while the actual server software remains unchanged. Usually, this functionality is used to create HTML documents on-the-fly as opposed to return fixed documents. This is referred to as dynamic and static content respectively. The former is primarily used for retrieving and/or inserting information to databases. The latter is, however, typically much faster. Highly niched web servers can be found in devices such as printers and routers in order to ease administration using a familiar user interface in the form of a web page.

History of web servers

In 1989 Tim Berners-Lee proposed to his employer CERN (European Organization 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, in 1990 Berners-Lee wrote two programs:

a browser called WorldWideWeb;
the world's first web server, later known as CERN httpd, which ran on NeXTSTEP.
Between 1991 and 1994 the simplicity and effectiveness of early technologies used to surf and exchange data through the World Wide Web helped to port them to many different operating systems and spread their use among lots of different social groups of people, first in scientific organizations, then in universities and finally in industry.

In 1994 Tim Berners-Lee decided to constitute the World Wide Web Consortium to regulate the further development of the many technologies involved (HTTP, HTML, etc.) through a standardization process.