• The 32-bit versions of Windows 7 support the execution of legacy DOS applications. A special Win32 process called ntvdm.exe is part of the operating system. When a legacy DOS application runs, ntvdm.exe is started to create a Virtual DOS Machine (VDM) environment for the DOS application. To the DOS application, it appears that it is running on a DOS computer. Access to computer hardware is virtualized through ntvdm.exe and the Win32 subsystem. A new instance of ntvdm.exe is created for each DOS application that is executed to ensure that the DOS ap- plications do not interfere with each other. DOS was not designed as a multitasking operating system, so this is the preferred behavior.
• It is common to find that DOS applications running on Windows 7 cannot run in full-screen mode. This is due to the fact that Windows 7 video drivers use a newer format that typically does not implement the video mode that DOS full-screen applications require. Users often expect such programs to work, as they did in Windows XP and Vista, after upgrading to Windows 7 and subsequently complain when these DOS programs do not run in full-screen mode. While it may be possible to downgrade the video diver on the computer to an older Windows XP version, there is no guarantee. The choice of video driver will be restricted by the computer hardware and the vendor's support for this atypical conf guration on Windows 7.


Read more about ntvdm at:
http://en.wikipedia.org/wiki/NTVDM.

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