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Knowledge Base > Operating Systems > Windows > NT/2K/XP/2003 > Windows 2000/XP/2003 is Assigning the Wrong Drive Letter to a Partition

Windows 2000/XP/2003 is Assigning the Wrong Drive Letter to a Partition

Windows 2000/XP/2003 uses a combination of disk signatures and partition start locations to keep track of drive letter assignment.  If the operating system finds a partition that matches this information, it will assign that drive letter to the partition (regardless of the file system in use).  Any additional partitions will then be assigned the next unused drive letter and added to its list.  This can cause problems to arise in the following situations:

  • A bootable Windows 2000/XP/2003 partition is duplicated and the original partition is in the MBR at the time the duplicated partition is booted.

  • A slide or move operation is performed on a bootable Windows 2000/XP/2003 partition and another partition is added or moved to start where the bootable Windows partition was originally located.

In the event of a drive lettering problem, the drive mappings in Windows 2000/XP/2003 can be reset using either of the two following methods:

  1. By using Regedt32 (Windows 2000) or Regedit (Windows XP/2003) to delete all of the values under the HKEY_LOCAL_MACHINE\System\MountedDevices registry key and then rebooting the system.  (If you have multiple MountedDevices keys in the registry, edit the one that has "\??\" and "\DosDevices\" entries under it.)

  2. By clearing the disk signature using BootIt BM, as follows:
    1. Entering the "Work with Partitions" dialog.
    2. Selecting the correct hard drive.
    3. Clicking the "View MBR" button.
    4. Clicking the "Clear Sig" button.
    5. Clicking the "Apply" button.

Once the drive mappings are reset, Windows will reassign the drive lettering using the standard procedure.

Note:  When using BootIt BM, you should not encounter this problem unless Windows 2000/XP/2003 is installed in a directory other than \WINDOWS\ or \WINNT\.


Please refer to the article "How to Prevent Boot Problems When Manipulating a Bootable Windows 2000/XP/2003 Partition" if you are planning to copy, slide, or move a Windows partition, from which you will later boot.  The advice in that article can help prevent problems booting later on.


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