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I need to run a 16-bit diagnostic tool in real mode under Windows XP, Vista, or 7. How can I accomplish this?

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Windows XP and later (Vista, 7) are based on the Windows NT kernel and don't rely on DOS, unlike Windows 3.1, 3.11, 95, 98, and ME. Windows Me dropped real-mode DOS support.

Windows NT includes a NTVDM (NT Virtual DOS Machine) that emulates a 16-bit DOS mode for 32-bit but not 64-bit versions.

If you really need to run tools that rely upon low level BIOS and hardware interface calls in 16-bit mode, you need to boot into a DOS environment completely outside of Windows.

FreeDOS an example of a separate 16-bit real mode DOS environment. You can install it into a separate partition, run it off of a live CD, or from a USB stick.

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    Or use a virtual machine? (Depending on what you are using the diagnostic tools for) Commented Aug 7, 2010 at 3:26
  • @MrStatic, the whole point is that the program needs access to the REAL hardware, not virtual. If it were happy with virtual hardware it would run fine under Windows.
    – psusi
    Commented Jul 19, 2012 at 14:58
  • @psusi, where did you get that from? It doesn’t specifically say it’s a hardware diagnostic program.
    – Synetech
    Commented Sep 1, 2012 at 22:42
  • @Synetech, because if it was happy running under a virtual machine, it would be happy running under the normal built in dos vm that windows has and uses to run dos programs, hence, the question would be moot. Also a 16 bit software diagnostic tool would be utterly useless when you aren't running a 16 bit os.
    – psusi
    Commented Oct 5, 2012 at 15:35
  • > It would be happy running under the normal built in dos vm that windows has and uses to run dos programs @psusi, unfortunately that’s not true. There are plenty of DOS software that won’t run correctly or at all in even XP’s NTVDM for one reason or another (vis 3D games).
    – Synetech
    Commented Oct 5, 2012 at 17:36

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