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Insight - real-mode DOS debugger

Copyright © 1993, 1996, 1997, 2002 Victor M. Gamayunov, Sergey Pimenov
Copyright © 2006-2009 Oleg O. Chukaev, Dmitry Vodyannikov, Goran Svitlica
[Under external link GNU General Public License]



Insight is a very small debugger for analyzing real-mode DOS programs. It features an i80486 disassembler, an i8086 assembler, 'Trace into' and 'Step over' functions, simple breakpoint handling, extended code or data navigation, simple color-highlighting, and a nice menu-driven interface comparable to Borland's Turbo Debugger.


Screenshot #1: Main window debugging '' (version 1.22).
Screenshot #1: Main window debugging (version 1.22).

Screenshot #2: Local menu for code window (version 1.22).
Screenshot #2: Local menu for code window (version 1.22).

System requirements

  • Intel i8086/88 microprocessor (or compatibles)
  • IBM EGA or VGA graphics card (or compatibles)
  • Microsoft MS-DOS 3.3 (or compatibles)
  • ~30 Kbytes free disk space
  • ~45 Kbytes free RAM

Version history


  • Alt+F5 and Alt+U (Show and Dump User Screen correspondingly) now work in the Dump window.
  • Fixed: Alt+L didn't work in the Dump window since version 1.20.
  • Fixed: Current line in the Code window highlighted incorrectly after entering assembler mode via Edit|Assembler.
  • Up and Down arrow keys sets and clears a flag in the Flags window.
  • Added 2 color schemes (TD and NC).
  • Fixed: Modification of SP or BP registers in some cases leads to general protection faults.


  • Alt+Z in the Dump window expands/shrinks it.
  • Home/End now work in the Dump window.
  • F6: skip current instruction.
  • Fixed: ^A in the Code window do not update the Stack window (try to change SP and then restore it in previous versions).
  • Stack window combined with Local variables / Function arguments window.
    Content of both windows can be edited (Shift+S in the Code window).
  • Fixed: CPU type displayed incorrectly on P-4. Thanks to Robert Riebisch.
  • Added 2nd page to the internal Help.
  • Current address of the Dump window and the Stack window displayed if corresponding window is in edit mode.
  • Current line in the Code window is highlighted even if this window is inactive.
  • Insight can be compiled with NASM 2.0+. Patch by Alex Buell.
  • Added support for some undocumented instructions. Suggested by Robert Riebisch.
  • whatsnew.* are no longer maintained. All changes are described in changes and changes.rus. Significant changes are marked with *, others -- with +.


  • Fixed: Insight hangs on 8086 and 286 machines after pressing Ctrl+R in the Code or Registers window.
  • Fixed: incorrect initial addresses of Code and Dump windows after loading program using F3.
  • Fixed: cursor in the code window disappears after executing INT 20 or INT 21 / 4C instruction using Run|Step over.
  • Added support for screen modes 90x25, 90x30, etc. This support requires changes in the Makefile and recompilation.
  • Zero-bytes are highlighted in the Dump window.
  • English documentation (insight.txt) corrected. Thanks to "Goxygen".
  • Changed e-mail address of Sergey Pimenov.


  • Added List Memory Blocks command (Ctrl+M in the code window).
  • Added Animate command (Run|Animate).
  • Large dump window if the screen have more than 25 lines and /e switch is used.
  • Command line, specified via Run|Arguments, now may be up to 126 bytes long. (Was: up to 80 bytes.)


  • Sources converted to NASM format.
  • Much internal changes and local optimizations (see the file CHANGES and the sources).
  • Documentation translated to English. [Translation by Dmitry Vodyannikov]
  • Help (F1).
  • Debugger shows the return code and type of termination of the program.
  • Full saving/restoring the VGA registers and font.
  • Did not work Ctrl+C in registers window. Now it works.
  • Line of hexadecimal numbers above the ASCII-part of dump.
  • Alt+U dumps the saved screen of the program (4,000 bytes from 0b800:0000).
  • Enter == Ctrl+F; Backspace == Ctrl+P.


  • Source code of debugger is released under GNU GPL.


Version 1.24: (250.0 Kbytes)
Version 1.23: (243.3 Kbytes)
Version 1.22: (235.1 Kbytes)
Version 1.21: (246.3 Kbytes)
Version 1.20: (235.8 Kbytes)
Version 1.10: (131.3 Kbytes)
Version 1.01 (no source code): insi101.rar (38.1 Kbytes)
Version 1.0 (no source code): insight.rar (37.3 Kbytes)

Page last modified on January 11, 2009.
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