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Microsoft KB Archive/102611

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Knowledge Base

Windows NT VDMs Keep Their Own System Time

Article ID: 102611

Article Last Modified on 10/31/2006


  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Advanced Server 3.1

This article was previously published under Q102611


Windows NT virtual DOS machines (VDMs) keep their own system time. Each time an MS-DOS-based application or a 16-bit Windows-based application is started, its BiosDataArea tick count is initialized to the current system time. When an MS-DOS-based application sets the time in a VDM, it is reflected in that VDM only. When a 16-bit Windows-based application changes the time, the new time is reflected in all 16-bit Windows-based applications running in Windows on Windows (WOW).


Windows NT is designed this way because MS-DOS-based applications depend on timer tic hardware for their sense of time. Many MS-DOS-based applications do not interact favorably with the timer tic hardware.

Additional query words: prodnt

Keywords: kbother KB102611