A web server is basically specialized software running on a computer, often no more powerful than the desktop variety. In fact, virtually any computer can run web server software. Both the Mac and the PC come with personal versions of web server software. The web server understands requests made from "clients" (visitors using a web browser) and presents requested HTML files along with images and other specialized content to the browser for viewing.
All web servers can handle standard HTML files, images in standard web formats (GIF, JPG, and often PNG), and with correct settings on the server rich media files like Flash, Quicktime, and Shockwave. All common web servers also have the ability to run scripts for processing data and a variety of functions. The language "Perl" is probably the most common and is available on most web servers. Javascript is widely known and very widely used but it is a "client side" scripting language because it is not processed by the server but rather by the browser. Perl requires that the script be processed by the server.
There are several other important technologies that can be implemented on a web server and perform important functions such as accessing a database and running a shopping cart to name but a few. Three of the most common are PHP, ASP, and Cold Fusion. You might think of them as competitors in the higher end server functionality game and all require a knowledge of how to write scripts in the different languages, but they all differ in the way they are made available.
PHP is open source and therefore is free. It is typically installed
on the machine running the web server and then processes the PHP tags
that are written into a standard HTML document. There are installations
of PHP written for most common platforms and you know you are on a
page using PHP by the suffix ".php". ASP (Active Server
Pages) is a Microsoft invention and originally required a Microsoft
server to be able to to make use of it. The actual scripting for ASP
is written in either Javascript or VBscript. You can tell you are
on a site using asp page by the ".asp" suffix but if you
view the source of an ASP page, you will see only standard HTML. The
server has processed the page, doing whatever dynamic tasks were called
for and displayed the results as plain HTML. It is now possible to
run ASP technology on non-Microsoft servers with Chilisoft ASP, which
essentially duplicates most of the operations of the Microsoft implementation.
The last, Cold Fusion, seen by the ".cfm" suffix on a ColdFusion
enabled server, is a proprietary language and server combination that
is now owned by Macromedia. Essentially, all of these technologies
extend the functionality of good 'ol HTML by providing database access
and a wealth of dynamic page processing features. There can be much
more to the web today than a static page.
