USB CD-ROM drive may have duplicate drive letters

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If you start Microsoft Windows 2000 on a computer that has a USB CD-ROM drive attached, the USB CD-ROM drive has two drive letters assigned to it.
This problem occurs because different managers assign drive letters during different parts of the startup sequence.

During startup, the Windows 2000 I/O Manager enumerates all present storage devices and tries to assign drive letters to each volume. Typically, I/O Manager assigns a drive letter by calling the mount manager. The mount manager is responsible for managing volume names.

In some cases, the mount manager cannot assign a drive letter to a device because the device is not yet available. When this occurs, I/O Manager creates the symbolic link for the drive letter itself, and the mount manager is not notified of the assigned drive letter.

When a USB CD-ROM drive is attached to the computer before startup, the I/O Manager might not assign a drive letter to the CD-ROM drive by means of the mount manager because, although the CD-ROM drive has been enumerated, the CD-ROM drive has not yet been started. In this case, I/O Manager assigns the drive letter itself by creating its own symbolic link for the drive letter.

Later in the startup sequence, the mount manager is notified that the USB CD-ROM drive has arrived. The mount manager then assigns another drive letter to the CD-ROM drive because it is unaware that a drive letter was previously assigned by I/O Manager. Therefore, two drive letters are assigned to the same USB CD-ROM drive.

Hotfix information

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.

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, submit a request to 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.


No prerequisites are required.

Restart requirement

You must restart your computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

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 Zone tab in the Date and Time tool in Control Panel.
   Date         Time   Version            Size    File name   --------------------------------------------------------------   26-Jun-2003  18:26  5.0.2195.6762      29,712  Mountmgr.sys
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
More information
For more information about how hotfix packages are named , click the following article number to view the article in the Microsoft Knowledge Base:
816915 New file naming schema for Microsoft Windows software update packages

Article ID: 822763 - Last Review: 01/11/2015 05:09:36 - Revision: 4.0

Microsoft Windows 2000 Server, Microsoft Windows 2000 Professional Edition, Microsoft Windows 2000 Advanced Server

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