Old Games and "The NTVDM CPU illegal instruction."

By Syrinth
Feb 11, 2007
  1. Hey, I'm trying to play some old games *The Quest for Glory series by Sierra* and I keep getting the following error:

    16 bit MS-DOS Subsystem
    <path name to the file I'm trying to use>
    The NTVDM CPU has encountered an illegal instruction.
    CS:c000 IP:00ac OP:ff ff ff ff ff Choose 'Close' to terminate the application.

    [close] [ignore]

    I used to be able to play these games on windows XP before but I recently built a new computer and have all new pieces. I've checked several other pages involving the NTVDM issue and have done my best to do what I can but whenever I try to open the games I get that problem.

    I've replaced the NTVDM.exe file with a new version of it to make sure that it was corrupted and am now confused. Yes I am aware that I can use DosBox but I really, really don't want to if that's at all possible.

    Lastly, I tried doing the SFCSCAN but I don't actually have the CD used to install my OS *mine was not working apparently so I used the computer shop's*

    Any help would be GREATLY appreciated.
  2. Syrinth

    Syrinth TS Rookie Topic Starter


  3. N3051M

    N3051M TS Evangelist Posts: 2,115

    try right clicking the .exe files and go to the compatibility tab and set it to windows 98 or 95..
  4. Syrinth

    Syrinth TS Rookie Topic Starter

    nope, it doesn't work sadly. :(
  5. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    Do you happen to have 64-bit Windows XP on your computer? If yes, then maybe that's your problem?

    If you don't like DOSBox, then maybe use VMWare? It's free for personal use :p
  6. Syrinth

    Syrinth TS Rookie Topic Starter

    What do you mean 64-bit windows xp?
  7. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    It is the version of Windows XP professional optimised for the new 64-bit PC processors made by AMD and Intel. Officially called "Windows XP Professional x64 Edition"
  8. Syrinth

    Syrinth TS Rookie Topic Starter

    ah, well no I don't have that lol :D
  9. andwan0

    andwan0 TS Rookie

    I used to get that exact same message with the exact same address/hex values.

    It's because of your new 64-bit CPU.

    NTVDM.exe allows 16-bit DOS programs to bypass the 32-bit Windows OS ... passing their 16-bit instructions directly to the CPU. Only 32-bit CPUs can understand 16-bit instructions (aswell as 32-bit instructions. But 64-bit CPUs can only understand 64-bit & 32-bit instructions...

    Using VMware won't help because VMware too transfers the DOS 16-bit instructions to your physical CPU because of NTVDM.EXE.... and if your CPU is of 64-bit nature then it'll throw up 16-bit instructions....
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