When IIS receives an HTTP request, it evaluates the URL to determine if the request is for static content (HTML), or dynamic content (ASP or ISAPI).
Request Processing Actions
| Request | Action |
| HTML Page | IIS returns the page immediately in HTML format. |
| ISAPI extension | IIS loads the ISAPI DLL (if it is not already running) and the request is sent to the extension through the Extension_Control_Block data structure. |
| File name extension mapped to a particular ISAPI extension | IIS loads the appropriate DLL file and presents the request through the Extension_Control_Block data structure. The .asp extension, for example, is mapped to Asp.dll, so that all requests for files with an .asp extension will be directed to Asp.dll. |
| CGI application | IIS creates a new process. IIS will then provide the query string and other parameters that are included with the request through the environment and standard input (STDIN) handle for the process. |