## IIS Request Processing

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.

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