What is Machine.config?

Machine configuration file: The machine.config file contains
settings that apply to the entire computer. This file is located in
the %runtime install path%Config directory. There is only one
machine.config file on a computer. The Machine.Config file found in
the “CONFIG” subfolder of your .NET Framework install directory
(c:WINNTMicrosoft.NETFramework{Version Number}CONFIG on Windows 2000
installations). The machine.config, which can be found in the
directory $WINDIR$Microsoft.NETFrameworkv1.0.3705CONFIG, is an XML-
formatted configuration file that specifies configuration options
for the machine. This file contains, among many other XML elements,
a browserCaps element. Inside this element are a number of other
elements that specify parse rules for the various User-Agents, and
what properties each of these parsings supports.
For example, to determine what platform is used, a filter element is
used that specifies how to set the platform property based on what
platform name is found in the User-Agent string. Specifically, the
machine.config file contains:
platform=Win95
platform=Win98
platform=WinNT
…
That is, if in the User-Agent string the string “Windows 95″
or “Win95″ is found, the platform property is set to Win95. There
are a number of filter elements in the browserCaps element in the
machine.config file that define the various properties for various
User-Agent strings.
Hence, when using the Request.Browser property to determine a user’s
browser features, the user’s agent string is matched up to
particular properties in the machine.config file. The ability for
being able to detect a user’s browser’s capabilities, then, is based
upon the honesty in the browser’s sent User-Agent string. For
example, Opera can be easily configured to send a User-Agent string
that makes it appear as if it’s IE 5.5. In this case from the Web
server’s perspective (and, hence, from your ASP.NET Web page’s
perspective), the user is visiting using IE 5.5, even though, in
actuality, he is using Opera.