When a user requests a static HTML page by clicking on a
link or entering the address, IIS running on the server
finds the page and sends it back to the client. However, if
the user requests a dynamic page, IIS sends the file to the
ASP.NET engine. The ASP.NET engine processes the page and
returns the results as pure HTML to IIS. IIS then returns
the HTML page to the client. That's why when you view the
source code of an ASP.NET page from within a Web browser,
you can't tell which information is dynamic and which is
static. The browser doesn't care if a page is dynamic or
static as long as it consists of HTML. IIS knows to send an
.aspx page (the asp.net extension) to the ASP.NET engine
because IIS maintains a list of application mappings. The
mappings indicate which program a file extension is
associated with.