Wikipedia
WIN.INI is a basic INI file that was used in versions of the Microsoft Windows operating environment up to Windows 3.11 to store basic settings at boot time. By default, all font, communications drivers, wallpaper, screen saver, and language settings were stored in WIN.INI by Windows 3.x. Many of these settings were honored in Windows 9x, although the files had begun to be phased out in favor of the Windows registry. Windows XP still acknowledged some entries in the WIN.INI file to provide backwards compatibility with older 16-bit applications. However, when a fresh install of XP is performed, the WIN.INI file created is initially blank, and in Windows Vista and Windows 7 the WIN.INI file was removed entirely.
Prior to Windows 3.0, it was not uncommon for applications to store their configuration settings inside WIN.INI. With the release of Windows 3.0 in 1990, Microsoft introduced the concept of "private" INI files, and some new application programming interface calls so that applications could store their settings in their own files. Today Microsoft recommends using other methods for storing settings.