INI is a file name extension used in Microsoft Windows. The letters stand for initialization. As this term implies, INI files are used to initialize, or set parameters for, the operating system and certain programs.
In Windows, two common INI files are SYSTEM.INI and WIN.INI. It is possible to get some idea of what these files do by opening them in a plain-text (ASCII) word processor or in a DOS editor. The files contain statements that set various parameters for the mouse, keyboard, peripherals, screen colors, passwords, and so on. Under ordinary circumstances, no changes should be made to these files in the text editor. (If the text editor presents the option to "Save changes" upon closing, click on "No.")
In Windows 95, 98, NT, and later versions, much of the configuration is done through values in the registry, rather than through INI files. Certain programs contain their own INI files. The contents of these files are normally modified by changing the characteristics of a program through the user interface for that program, not by editing the files themselves.