Machine configuration file. This file is located in the %runtime installation path%\Config directory. The machine configuration file contains settings that affect all the applications that run on the machine.
Application configuration file. This file contains the settings required to configure an individual application. ASP.NET configuration files are named Web.config, and application configuration files are named App.exe.config, where App.exe is the name of the executable.
Security configuration file. The security configuration files contain security permissions for a hierarchy of code groups. The security configuration files define the enterprise-level, machine-level, and user-level security ?policies. The Enterprisesec.config file defines the security policies for the enterprise. The machine-level Security.config file defines the security policy for the machine, whereas the user-level Security.config file defines the security policy for a user.