ANSI.SYS

ANSI.SYS is a device driver in the DOS family of operating systems that provides extra console functions through ANSI escape sequences. It is partially based upon a subset of the text terminal control standard proposed by the ANSI X3L2 Technical Committee on Codes and Character Sets (the "X3 Committee").

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
• /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

Once loaded, ANSI.SYS enables code sequences to apply various text formatting features. Using this driver, programs that write to the standard output can 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. It also allows for the changing of the video mode from standard 80×25 text mode to a number of different graphics modes (for example, 320×200, 640×40-column text mode) depending on which video graphics card is installed.

The standard ANSI.SYS is relatively slow as it maps escape sequences to the equivalent BIOS calls. Several companies made third-party replacements that interface directly with the video memory, in a similar way to most DOS programs that have a full-screen user interface.

By default, the internal DOS command CLS works by directly calling the corresponding BIOS function to clear the screen, thereby prominently violating the hardware abstraction model otherwise maintained. However, if an ANSI driver is detected by the DR-DOS COMMAND.COM, it will instead send the control sequence defined in the reserved environment variable $CLS to the attached console device.^[1] If the environment variable is undefined, it falls back to send the sequence ESC [ 2 J instead.^[1] Specifying other sequences can be used to control various screen settings after a CLS. Due to the difficulties to define environment variables containing binary data COMMAND.COM also accepts a special \nnn notation for octal numbers.^[1] For example, to send an alternative control sequence like ESC + (for 1Bh 2Bh as used by ASCII terminals), one could define the variable as follows:

SET $CLS=\033+

These features are supported by COMMAND.COM in all versions of DOS Plus and DR-DOS, but not in MS-DOS or PC DOS. They are also supported by the command interpreters in Concurrent DOS, Multiuser DOS and REAL/32, although they use VT52 rather than ANSI control sequences by default (e.g. ESC E).

Keyboard remapping

An interesting feature of ANSI.SYS is the ability to remap any key on the keyboard in order to perform shortcuts or macros for complex instructions. Using special escape sequences, the user can define any keystroke that has a character-code mapping to simulate an arbitrary sequence of such keystrokes. This feature was also used by evildoers to create simple trojans out of text files laced with nefarious keyboard remaps, known as "ANSI bombs". A number of products were released to protect users against this:

• Some antivirus utilities contained functionality to ensure that, for example, the F3 function key isn't remapped to DEL *.* or FORMAT C: and the N-key (for no) isn't remapped to Y.
• Some versions of ANSI.SYS support a command line switch to disable the key remapping feature.
• Some of the third-party ANSI.SYS replacements were deliberately designed not to support the keyboard remapping functions.
• PKWARE produced a TSR program, PKSFANSI (PK Safe ANSI), which filters out keyboard remapping escape codes as they are written to the standard output.^[2] This has the advantage that the user can load some useful remappings from a text file and then run PKSFANSI to prevent further, possibly malicious remappings.

Occurrence

ANSI.SYS appeared in MS-DOS 2.0, the first version of the operating system supporting device drivers.^[3] It is a part of several other Microsoft operating systems, including:

• Windows 95
• Windows 98
• Windows NT
• Windows 2000
• Windows XP
• Windows Server 2003 (x86 versions)
• Windows Vista

It is also present in many non-Microsoft DOS systems, e.g. IBM PC DOS and DR-DOS.

ANSI.SYS was required to run some software that used its cursor and color control functions. It could also be used to enable elaborate color codes in the COMMAND.COM prompt. These uses were overshadowed by the use of ANSI.SYS in BBSes; ANSI escape sequences were used to enable BBSes to send elaborate text graphics more elaborate than ASCII art, and to control the cursor in ways that were used in a number of online games and similar features.

Features

CSI (Control Sequence Introducer) is a placeholder for the common two-byte escape lead-in sequence "ESC [" (that is, 0x1B 0x5B). The ANSI standard also defines an alternative single-byte CSI code 0x9B, which is not supported by ANSI.SYS.

Standard DOS ANSI.SYS drivers support only the following sub-set of ANSI escape sequences:

There are also some escape sequences specific to the implementation of ANSI.SYS. They are not generally supported by ANSI consoles in other operating systems.

In some DOS implementations, video modes above 7 are not documented. Under Multiuser DOS, the only valid argument in conjunction with PCTERM is 7.

Notes

1. 1 2 Arguments 0,1,2 are only supported and distinguished by Japanese versions of MS-DOS and PC DOS ANSI.SYS. Western issues of ANSI.SYS will not support or not distinguish between them. They are, however, also supported by Multiuser DOS.
2. 1 2 3 4 Lead-in prefix '>' is only supported in Japanese versions of MS-DOS, PC DOS and DR-DOS ANSI.SYS to access special Japanese display modes.
3. ↑ This non-standard escape sequence is only supported by MS-DOS and PC DOS ANSI.SYS. It can be used to enable or disable extended keyboard support at runtime similar to the ANSI.SYS /X startup option.
4. 1 2 These non-standand escape sequences to insert and delete lines are only supported by Japanese versions of MS-DOS and PC DOS. They are also supported by Western issues of Multiuser DOS, but not by DR-DOS.
5. 1 2 These non-standard escape sequences to switch between the Korean and English keyboard input modes are only supported by Korean versions of MS-DOS, PC DOS and DR-DOS ANSI.SYS.
6. 1 2 These non-standard escape sequences to disable and reenable any output to the CON: device are supported by ANSI.SYS of DR-DOS 7.02 and higher only. They are used to mute the console output during boot, for example in conjunction with DR-WebSpyder boot floppies.
7. ↑ A value of 7 is used to either enable (with SM) or disable (with RM) the wrap around at the end of rows. If enabled, the option causes extra characters to wrap onto the next line, while these characters will be lost, if wrapping is disabled.
8. 1 2 Video modes 114 and 115 are only supported by Japanese DOS/V issues of ANSI.SYS found in DR DOS 6.0, Novell DOS 7 and higher.

References

See also

• ANSI escape sequence

External links

• DR-DOS 7 user documentation, description of ANSI.SYS escape sequences (incomplete)
• Modifying the DOS prompt with ANSI.SYS
• Guide to using ANSI.SYS
• Ansilove/PHP A set of tools for converting ANSi/BiN/ADF/iDF/TUNDRA/XBiN files into PNG images
• ANSI.SYS keyboard codes from µVGA