Each computer with the .NET Framework installed has a machine configuration file. This file, named Machine.config, contains settings that apply to the entire computer. It is located in the %runtime install path%\Config directory. Machine.config contains configuration settings for machine-wide assembly binding, built-in remoting channels, and ASP.NET.
The Machine.config file can be used by administrators to specify assembly binding restrictions that are local to that computer. The settings in the machine configuration file take precedence over all other configuration settings; however, this does not mean that all configuration settings should be put in this file. Some settings in the machine configuration file cannot be changed by other configuration files. For example, the common language runtime version specified in the machine configuration file is final, and cannot be overridden. Overrides specified in the Machine.config file affect all applications.
See the following topics in the .NET Framework SDK documentation: Machine Configuration Files, Configuration Files.