Assume the following scenario. In Microsoft Windows XP, you
run a 16-bit application for which the following conditions are true:
- The application is running in a Windows NT Virtual DOS Machine (NTVDM)
- The application accesses a COM port on the computer.
this scenario, you notice that another 16-bit or
32-bit application cannot access the same COM port until you quit the first
This problem occurs because the NTVDM CommsAutoClose setting
does not work in Windows XP. Specifically, the code that handles the
CommsAutoClose registry entry is not included in Windows XP.
A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.
If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix. Note
If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note
The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.
You must have Windows XP Service Pack 1 (SP1) or Windows XP
Service Pack 2 (SP2) installed before you apply this hotfix.
You do not have to restart the computer after you apply this
Hotfix replacement information
This hotfix does not replace any other hotfixes.
The English version of this hotfix has the file
attributes (or later file attributes) that are listed in the following table.
The dates and times for these files are listed in Coordinated Universal Time
(UTC). When you view the file information, it is converted to local time. To
find the difference between UTC and local time, use the Time
tab in the Date and Time tool in Control
Panel.Windows XP Service Pack 1
Windows XP Service Pack 2
Date Time Version Size File name
01-Dec-2004 06:03 22.214.171.124 92,224 Krnl386.exe
01-Dec-2004 05:56 33,840 Ntio.sys
01-Dec-2004 05:56 34,560 Ntio404.sys
01-Dec-2004 05:56 35,648 Ntio411.sys
01-Dec-2004 05:56 35,424 Ntio412.sys
01-Dec-2004 05:56 34,560 Ntio804.sys
19-Jan-2005 03:37 5.1.2600.1620 396,800 Ntvdm.exe
04-Jun-2004 00:43 5.1.2600.1562 245,760 Wow32.dll
Date Time Version Size File name
19-Jan-2005 03:12 5.1.2600.2598 420,352 Ntvdm.exe
Microsoft has confirmed that this is a bug in the Microsoft
products that are listed in the "Applies to"
For more information, click the following article
number to view the article in the Microsoft Knowledge Base:
Description of the standard terminology that is used to describe Microsoft software updates
For more information about the same
problem in Microsoft Windows 2000, click the following article number to view
the article in the Microsoft Knowledge Base:
NTVDM CommsAutoClose setting does not work in Windows 2000