About web application servers :

• To understand ColdFusion, you must first understand the role of web application servers. Typically, web browsers make requests, and web servers, such as Microsoft Internet Information Server (IIS) and the Apache web server, fulfill those requests by returning the requested information to the browser. This information includes, but is not limited to, HTML and Adobe Flash files.

• A web server's capabilities are limited because all it does is wait for requests to arrive and attempt to fulfill those requests as soon as possible. A web server does not let you do the following tasks:

1. Interact with a database, other resource, or other application.
2. Serve customized information based on user preferences or requests.
3. Validate user input.

• A web server, basically, locates information and returns it to a web browser.

• To extend the capabilities of a web server, you use a web application server, a software program that extends the web server's capabilities to do tasks such as those in the preceding list.