ANSI.SYS (pronounced "ansee dot sis") is a driver file a little software module, or controller used by MSDOS and OS/2, ANSI.SYS tells the computer how to display information based on the standard codes adopted by the American National Standards Institute (ANSI). Each code in the ANSI table represents either a character (like the letter S) or a number (such as the number 5), and other keys found on the keyboard (such as the Enter key). Some codes in the table are not found on the keyboard, but programs use them for specific purposes (such as making the PC beep, or moving the cursor to the next line on-screen).
The ANSI.SYS file contains the instructions for displaying each of the characters found on the keyboard (such as the S or the 5). In addition, it contains instructions for moving the cursor when appropriate (when the Backspace key is pressed, for example), and for sending signals to other devices (like the signal indicating when to sound the beep, or when to move the paper in the printer). Most of the control codes in the ANSI table were designed for old style terminals, so a small section of the ANSI table is no longer used. However, some programs adhere to the ANSI standard and require the ANSI.SYS file. Therefore, some computer programs require that the statement, DEV1CE=C:\DOS\ANSI.SYS be included within a system configuration file called CONFIG.SYS. When the computer is booted, this statement loads the driver file ANSI.SYS into memory, where its instructions can be accessed by any program. You can use many new commands, giving you more control over your screen and keyboard, than you have using standard MS-DOS commands.