System Configuration Changes

Oct 13, 2025 by wbrum.org 137 views

Introduction

In this article, we will discuss the issue of DOS devices to directory (also known as permanent SUBST) not being honored after the Windows 21H1 update. We will explore the possible causes of this issue and provide potential solutions to resolve it.

Background

Previously, a device mapping had been established using HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\DOS Devices to add an alias from D:\ to C:\Build. This approach was discussed in various online forums and was widely used by users to create a permanent SUBST mapping.

The Issue

After the Windows 21H1 update, many users reported that their DOS devices to directory mappings were no longer honored. This meant that the alias created using the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\DOS Devices registry key was not being recognized by the system.

Possible Causes

There are several possible causes for this issue:

Registry Key Changes: The Windows 21H1 update may have made changes to the registry key used to create DOS devices to directory mappings. This could have caused the system to ignore the existing mappings.
Driver Updates: The update may have also included driver updates that affected the way the system handles device mappings.
System Configuration Changes: The update may have made changes to the system configuration that affected the way the system handles device mappings.

Troubleshooting Steps

To troubleshoot this issue, follow these steps:

Check the Registry Key: Verify that the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\DOS Devices registry key exists and has the correct values.
Check for Driver Updates: Check for any driver updates that may have been included in the Windows 21H1 update.
Check System Configuration: Check the system configuration to see if any changes were made that may have affected the way the system handles device mappings.
Recreate the Mapping: Try recreating the device mapping using the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\DOS Devices registry key.

Potential Solutions

If the troubleshooting steps do not resolve the issue, try the following potential solutions:

Use a Different Registry Key: Try using a different registry key to create the device mapping. For example, you can use HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\MountPoints2.
Use a Third-Party Tool: Consider using a third-party tool to create the device mapping. These tools can often provide more flexibility and control over the mapping process.
Reinstall Windows: If all else fails, you may need to reinstall Windows to resolve the issue.

Conclusion

In conclusion, the issue of DOS devices to directory (aka permanent SUBST) not being honored after the Windows 21H1 update is a complex one. There are several possible causes, and troubleshooting the issue requires a thorough understanding of the system configuration and registry keys. By following the troubleshooting steps and potential solutions outlined in this article, you should be able to resolve the issue and get your device mappings working again.

Additional Resources

For more information on this issue, you can refer to the following resources:

Microsoft Support: Microsoft provides support for Windows 21H1 and can help you troubleshoot the issue.
Online Forums: Online forums such as Reddit and Stack Overflow can provide valuable insights and solutions from other users who have experienced similar issues.
Third-Party Tools: Consider using third-party tools to create device mappings. These tools can often provide more flexibility and control over the mapping process.

Frequently Asked Questions

Q: What is the cause of the issue? A: The cause of the issue is not clear, but it may be related to changes made to the registry key or system configuration.
Q: How do I troubleshoot the issue? A: To troubleshoot the issue, follow the steps outlined in this article.
Q: What are the potential solutions? A: The potential solutions include using a different registry key, using a third-party tool, or reinstalling Windows.
DOS Devices to Directory (aka Permanent SUBST) Not Honored After Windows 21H1 Update: Q&A =====================================================================================

Q: What is the issue with DOS devices to directory (aka permanent SUBST) after the Windows 21H1 update?

A: The issue is that the device mappings created using the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\DOS Devices registry key are no longer being honored by the system. This means that the alias created using this registry key is not being recognized by the system.

Q: What are the possible causes of this issue?

A: There are several possible causes of this issue, including:

Registry Key Changes: The Windows 21H1 update may have made changes to the registry key used to create DOS devices to directory mappings.
Driver Updates: The update may have also included driver updates that affected the way the system handles device mappings.
System Configuration Changes: The update may have made changes to the system configuration that affected the way the system handles device mappings.

Q: How do I troubleshoot this issue?

A: To troubleshoot this issue, follow these steps:

Check the Registry Key: Verify that the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\DOS Devices registry key exists and has the correct values.
Check for Driver Updates: Check for any driver updates that may have been included in the Windows 21H1 update.
Check System Configuration: Check the system configuration to see if any changes were made that may have affected the way the system handles device mappings.
Recreate the Mapping: Try recreating the device mapping using the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\DOS Devices registry key.

Q: What are the potential solutions to this issue?

A: The potential solutions include:

Use a Different Registry Key: Try using a different registry key to create the device mapping. For example, you can use HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\MountPoints2.
Use a Third-Party Tool: Consider using a third-party tool to create the device mapping. These tools can often provide more flexibility and control over the mapping process.
Reinstall Windows: If all else fails, you may need to reinstall Windows to resolve the issue.

Q: Can I use a third-party tool to create the device mapping?

A: Yes, you can use a third-party tool to create the device mapping. These tools can often provide more flexibility and control over the mapping process.

Q: What are some popular third-party tools for creating device mappings?

A: Some popular third-party tools for creating device mappings include:

SubstIt: SubstIt is a free tool that allows you to create and manage device mappings.
DriveMapper: DriveMapper is a commercial tool that allows you to create and manage device mappings.
DiskMapper: DiskMapper is a free tool that allows you to create and manage device mappings.

Q: Can I reinstall Windows to resolve the issue?

A: Yes, if all else fails, you may need to reinstall Windows to resolve the issue.

Q: What are some best practices for creating device mappings?

A: Some best practices for creating device mappings include:

Use a consistent naming convention: Use a consistent naming convention for your device mappings to avoid confusion.
Use a unique drive letter: Use a unique drive letter for each device mapping to avoid conflicts.
Test the mapping: Test the mapping to ensure that it is working correctly.

Q: Can I use a script to create the device mapping?

A: Yes, you can use a script to create the device mapping. This can be useful if you need to create multiple device mappings.

Q: What are some popular scripting languages for creating device mappings?

A: Some popular scripting languages for creating device mappings include:

Batch: Batch is a scripting language that is built into Windows.
PowerShell: PowerShell is a scripting language that is built into Windows.
Python: Python is a popular scripting language that can be used to create device mappings.

Q: Can I use a registry editor to create the device mapping?

A: Yes, you can use a registry editor to create the device mapping. This can be useful if you need to create a device mapping that is not supported by the built-in tools.

Q: What are some popular registry editors for creating device mappings?

A: Some popular registry editors for creating device mappings include:

Regedit: Regedit is a built-in registry editor that comes with Windows.
Regedit64: Regedit64 is a 64-bit version of Regedit that can be used to create device mappings on 64-bit systems.
RegeditX: RegeditX is a third-party registry editor that can be used to create device mappings.