How to Machine.Config
In ASP.NET, configuration information is stored in one of two files: machine.config or web.config. Machine.config file is using as root configuration file and provides ASP.NET configuration settings for every application in the Web server. Machine.config configuration file comes with the Microsoft .NET Framework and contains the default settings. While an application can have as many web.config files as it has directories and subdirectories , there is only one machine.config file per machine.
The Machine.config file is located in the folder %windir%\Microsoft.NET\Framework\%version%\config, where %version% is a folder that is named for the current installed version of the .NET Framework. Machine.config file contains the default configuration information for every web application, as well as other application types, on the machine. The machine.config file is processed first and any values specified within the machine .config file are inherited throughout every ASP.NET application on your Web server.