ANSI.SYS
DOS device driver
ANSI.SYS is a device driver in the DOS family of operating systems that allows a program to control the display by inserting ANSI escape sequences into its output. Without this a program could only add lines of text to the bottom of the screen, unless it directly manipulated the graphics hardware. Using ANSI.SYS would have allowed graphics device independence in IBM clones; but it was not installed by default and was notoriously slow.
Usage
To use ANSI.SYS under DOS, a line is added to the CONFIG.SYS (or CONFIG.NT under Windows NT based versions of Windows) file that reads:
DEVICE=drive:\path\ANSI.SYS options
where drive: and path are the drive letter and path to the directory in which the file ANSI.SYS is found, and options can be a number of optional switches to control the behaviour. ANSI.SYS may also be loaded into upper memory via DEVICEHIGH/HIDEVICE.
/K use extended keyboard BIOS functions (INT 16h) rather than standard ones This made the F11 and F12 keys work.
/L force number of lines
/R adjust line scrolling to support screen readers
/S or /SCREENSIZE set screensize
/X support redefinition of extended key codes independent of standard codes
Functionality
Using this driver, programs that write to the standard output can write escape sequences to make use of the 16 text foreground colors and 8 background colors available in VGA-compatible text mode, make text blink, change the location of the cursor on the screen, and blank the screen. They could also change the video mode from standard 80×25 text mode to a number of different graphics modes (for example, 320×200 graphics mode with text drawn as pixels, though ANSI.SYS is not able to turn individual pixels on and off).
The standard ANSI.SYS is very slow as it changed the screen using BIOS calls (which needed two calls to put a character on the screen and move the cursor right). Several companies made third-party replacements that interface directly with the video memory and ran at usable speeds, examples are ANSI.COM, NANSI.SYS and ANSIPLUS.EXE.
COMMAND.COM checked if this driver was in use, and changed the CLS command to use an escape sequence instead of a BIOS call.
Keyboard remapping
An interesting (mis)feature of ANSI.SYS is the ability to remap any key on the keyboard in order to perform shortcuts or macros for complex instructions.
“ANSI.SYS” enters the record as dOS device driver. Crown Archives preserves that source wording while asking what ANSI, device and driver can confirm, complicate or overturn.
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The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated May 3, 2026. The linked authority identifier is Q905270. None of the 0 selected statements returned an explicit reference.
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