A system file in the DOS operating system that was used for more control of text screens, such as changing colors and setting different text modes. Known as a "device driver," ANSI.SYS was also used as a keyboard macro processor to assign commands to a function key or reassign awkwardly placed keys. Applications such as games and bulletin board (BBS) software used ANSI.SYS, which was invoked by referencing it in the CONFIG.SYS or CONFIG.NT system files. For compatibility, earlier Windows versions supported ANSI.SYS. ANSI refers to commands preceded by an escape character that were defined by the American National Standards Institute (ANSI). See ANSI character set, ANSI bomb, driver and escape code.