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").

As it was not installed by default, and was notoriously slow, little software took advantage of it and instead resorted to directly manipulating the IBM PC hardware. A number of third-party alternatives that ran at reasonable speed were created, such as ANSI.COM,[1] NANSI.SYS[2] and ANSIPLUS.EXE[3] to attempt to change this.

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[4] This made the F11 and F12 keys work.
  • /L force number of lines
  • /R adjust line scrolling to support screen readers[4]
  • /S or /SCREENSIZE set screensize
  • /X support redefinition of extended key codes independent of standard codes[4]

Functionality

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 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 relatively slow as it maps escape sequences to BIOS calls (which managed to be designed so that two calls were needed 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, 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.[5]

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.[6] This feature was also used 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 versions of ANSI.SYS support a command line switch to disable the key remapping feature, f.e. the option /S (Secure) in ANSI.SYS of Datalight ROM-DOS[7] or NANSI.SYS[2] of FreeDOS. Other ANSI drivers like ANSIPLUS can be configured to disable the redefinition of keys as well.[3]
  • Setting CONFIG.SYS SCREEN=ANSI in PTS-DOS provides a built-in ANSI driver not supporting the keyboard remapping functions.[8][9]
  • Some of the third-party ANSI.SYS replacements were deliberately designed never to support the keyboard remapping functions.
  • PKWARE produced a terminate-and-stay-resident program, PKSFANSI (PK Safe ANSI), which filters out keyboard remapping escape codes as they are written to the standard output.[10] 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.[11] It was supported by all following versions of MS-DOS. It is also present in many non-Microsoft DOS systems, e.g. IBM PC DOS and DR-DOS.[12]

ANSI.SYS was required to run some software that used its cursor and color control functions.[12] 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 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.

Most versions of Windows did not support ANSI escape codes in any useful way (it could be used by MSDOS emulation in some versions). In Windows 10 support for similar escape sequences was built into the Win32 console (the text terminal window), but must be activated using the Windows API function SetConsoleMode by setting the ENABLE_VIRTUAL_TERMINAL_PROCESSING flag.[13]

Features

CSI (Control Sequence Introducer) is a placeholder for the common two-byte escape lead-in sequence "ESC [" (that is, 0x1B 0x5B).[12] The ANSI standard also defines an alternative single-byte CSI code 0x9B, which is not supported by ANSI.SYS (this code instead drew a cent sign ⟨¢⟩ from CP437).

Standard DOS ANSI.SYS drivers support only the following sub-set of ANSI escape sequences:[12]

SequenceEffect
ESC [ r ACursor up (CUU)
ESC [ r BCursor down (CUD)
ESC [ c CCursor forward (CUF)
ESC [ c DCursor back (CUB)
ESC [ r;c fHorizontal and vertical position (HVP)
ESC [ r;c HCursor position (CUP)
ESC [ n JErase display (ED) (n=0, 2 or n=0, 1, 2)[nb 1]
ESC [ n KErase in line (EL) (n=0 or n=0, 1, 2)[nb 1]
ESC [ n mSelect graphic rendition (SGR) (n=0..47)
ESC [ 6 nDevice status report (DSR) requests cursor position,
returned as cursor position report (CPR):
ESC [ r;c R
ESC [ sSave cursor position (SCP)
ESC [ uRestore cursor position (RCP)

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.

SequenceEffect
ESC [ n h
ESC [ ?n h
ESC [ =n h
ESC [ >n h[nb 2]		Set screen mode (SM)[nb 2]
ESC [ n l
ESC [ ?n l
ESC [ =n l
ESC [ >n l[nb 2]		Reset screen mode (RM)[nb 2]
ESC [ n qEnable (n=1) or disable (n=0) /X support[nb 3]
ESC [ LInsert line (IL)[nb 4]
ESC [ MDelete line (DL)[nb 4]
ESC $ ) 1Switch keyboard input mode to Korean (Hangul)[nb 5]
ESC ( 2Switch keyboard input mode to English[nb 5]
ESC [ +Enable console output[nb 6]
ESC [ -Disable console output[nb 6]
ESC [ a;b;... p Set key re-definement (SKR/KR)
Screen modes
ModeDescriptionModeDescription
040 × 25 monochrome 140 × 25 color
280 × 25 monochrome 380 × 25 color
4320 × 200 color 5320 × 200 monochrome
6640 × 200 monochrome
7Wrap at end of line[nb 7]
13320 x 200 color (graphics) 14640 x 200 color (16-color graphics)
15640 x 350 monochrome (2-color graphics) 16640 x 350 color (16-color graphics)
17640 x 480 monochrome (2-color graphics) 18640 x 480 color (16-color graphics)
19320 x 200 color (256-color graphics)
114640 x 480 color (16-color graphics)[nb 8] 115640 x 475 color (16-color graphics)[nb 8]

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

See also

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

  1. ↑ Mefford, Michael (1989-02-07). "ANSI.com: Download It Here". PC Magazine. Retrieved 2011-08-10.
  2. 1 2 Kegel, Daniel; Almy, Tom; Auer, Eric (1999-02-28). "NANSI – An Enhanced MS-DOS Console Driver". 4.0. Dan Kegel's Web Hostel. Archived from the original on 2018-05-19. Retrieved 2011-08-10.
  3. 1 2 Sweger, Kristofer (2007) [2000]. "Configuring ANSIPLUS". Archived from the original on 2018-10-04. Retrieved 2018-10-04.
  4. 1 2 3 "Guide to using ANSI.SYS". Archived from the original on 2007-06-23. Retrieved 2017-09-11.
  5. ↑ Paul, Matthias R. (1997-07-30) [1994-05-01]. NWDOS-TIPs — Tips & Tricks rund um Novell DOS 7, mit Blick auf undokumentierte Details, Bugs und Workarounds. Release 157 (in German) (3 ed.). Archived from the original on 2017-09-10. Retrieved 2014-08-06. {{cite book}}: |work= ignored (help) (NB. NWDOSTIP.TXT is a comprehensive work on Novell DOS 7 and OpenDOS 7.01, including the description of many undocumented features and internals. It is part of the author's yet larger MPDOSTIP.ZIP collection maintained up to 2001 and distributed on many sites at the time. The provided link points to a HTML-converted older version of the NWDOSTIP.TXT file.)
  6. ↑ "ANSI Keyboard codes - ANSI.SYS Key and Extended Key Codes". µVGA - VGA Microcontroller interface. SECONS Ltd. 2012. Archived from the original on 2017-09-11. Retrieved 2017-09-11.
  7. ↑ Datalight, Inc.; GPvNO (April 2005) [1999]. "Datalight ROM-DOS User's Guide" (PDF). Datalight, Inc. 3010-0200-0716. Retrieved 2018-09-16.
  8. ↑ "PTS-DOS 2000 Pro User Manual" (PDF). Buggingen, Germany: Paragon Technology GmbH. 1999. Archived (PDF) from the original on 2018-05-12. Retrieved 2018-05-12.
  9. ↑ Günther, Jens; Ernst, Tobias (2004-04-25) [1996]. Ellsässer, Wolfgang (ed.). "Inoffizielle deutschsprachige PTS-DOS-FAQ (PTS/FAQD)" [Inofficial German PTS-DOS FAQ] (in German). Retrieved 2018-10-02.
  10. ↑ Massingill, Michael D. Pearson, Dave (ed.). "PK SAFE ANSI (PKSFANSI.COM)". Archived from the original on 2017-09-11. Retrieved 2017-09-11.
  11. ↑ Field, Tim (November 1983). "Installable Device Drivers for PC DOS 2.0 - Inside the IBM PC". BYTE. 8 (11): 188–196. Retrieved 2016-03-19.
  12. 1 2 3 4 "Chapter 9: Configuring the System". Caldera, Inc. 1998. Archived from the original on 2017-09-10. Retrieved 2017-09-10. (NB. DR-DOS 7 user documentation, description of ANSI.SYS escape sequences (incomplete))
  13. ↑ "Console Virtual Terminal Sequences". Windows Console. 20 September 2022.
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