A file that contains configuration information for a particular program. When the program is executed, it consults the configuration file to see what parameters are in effect. The configuration file for DOS is called CONFIG.SYS. Older versions of the Windows operating system stores configuration information in files with a.INI extension. The two most important configuration files are WIN.INI and SYS.INI. Starting with Windows 95, most configuration information is stored in MIF files and in the Registry.