(NT Virtual DOS Machine) Windows software that runs 16-bit DOS applications. The NTVDM module comes with 32-bit versions of Windows starting with Windows NT but not 64-bit versions (see Windows XP Mode). Each application runs in its own NTVDM, and crashes do not affect regular 32-bit Windows programs or other 16-bit apps running in their own NTVDMs. Windows on Windows Windows on Windows (WOW16) uses NTVDM to enable 16-bit Windows 3.x apps to run, and API calls in Win3.x are converted into their NT equivalents and run in 32-bit native mode. See Virtual 8086 Mode.