Reserving a Letter for the CD-ROM Drive

Source: 1997 Chin (can be freely distributed as long as I'm given credit). Visit

To prevent the CD-ROM/DVD/Optical drive letter from changing when additional hard disc drives or partitions are added to a computer system, one needs to specify or reserve a specific drive letter for the CD-ROM drive. Use a drive letter other than drive D: and high enough in the alphabet to accommodate any additional drives that are added to or removed from the system. Reserving a specific drive letter for the CD-ROM drive is also a good idea if your computer system accesses a network. I usually use drive R: for the CD-ROM drive.

This procedure should be implemented before any software that will need to access the CD-ROM drive is installed. Naturally, this procedure can also be used after software has already been installed. Some programs, e.g. Microsoft Bookshelf, will prompt you to select a different drive to access the CD-ROM from. Other software may have to be reinstalled to get it to use the new drive letter for the CD-ROM drive.

Windows 2000 and XP

  1. Log on as Administrator or as a member of the Administrators group.
  2. Right click on My Computer and choose Manage from the context menu
  3. Go to Storage > Disk Management
  4. Right-click the CD-ROM/DVD drive that you want to change the drive letter of, and then click Change Drive Letter.
  5. Select R: for the new drive letter.
  6. Click OK.

Windows 95/98/Me

  1. Open Control Panel.
  2. Then double click on the System icon to load the System Properties utility.
  3. Click on the Device Manager tab.
  4. Click on the plus sign to the left of CD-ROM to display the list of CD-ROM drives.
  5. Click once on the CD-ROM drive that is listed. e.g. NEC CD-ROM DRIVE:222.
  6. Click on the Properties button.
  7. Click on the Settings tab.
  8. In the Reserved drive letters box, Change "Start drive letter:" to R: , "End drive letter:" should automatically change to R:. If it didn't, click on the arrow and select R: from the list.
  9. Click on the OK button to close the Properties windows and accept the new settings.
  10. Click on the OK button to close the System Properties utility window.
  11. Click on the Yes button to restart your computer to allow the new setting to take effect.

Note: If you do not need to access the CD-ROM drive from DOS, you can skip the following.

From DOS / Command Mode

To insure that the same drive letter is used for both the "Command Mode" and within the GUI for Windows 95/98, the CD-ROM device driver and MSCDEX.EXE must be loaded when your computer is started.


The CD-ROM device driver for your CD-ROM drive must be loaded from CONFIG.SYS.


The LastDrive= setting in CONFIG.SYS limits the range of drive letters you can assign to the CD-ROM. If LastDrive= is set to a value lower than the letter you want to use, raise it.



Then the command,


has to be run before the GUI for Windows 95/98. You can put the command into AUTOEXEC.BAT or into a separate batch file that is called from AUTOEXEC.BAT.

I created a separate batch file named LD-CDEXT.BAT (Load CD-ROM Extensions) to load MSCDEX.EXE with the proper parameters to configure the OS to use R: for the CD-ROM drive. LD-CDEXT.BAT is called from the AUTOEXEC.BAT file using the command CALL LD-CDEXT.BAT. This is a safety measure to protect against the possibility of AUTOEXEC.BAT being modified or overwritten by an installation program and loosing the proper syntax for loading MSCDEX.EXE.

Now you can add or remove hard disc drives or change the number of partitions without having to worry about the drive letter for the CD-ROM drive changing.

Any CD-ROM programs that you installed earlier will now be unable to find the CD-ROM drive. Some will ask you for the new location; others will simply fail to run.

For those programs that were already installed, you can use a program called Change of Address (CoA) to change the references to the old CD-ROM drive letter to the new drive letter that are in the Windows Registry and .INI files.

In CoA, use the old drive letter followed by a colon as the old address, and use the new drive letter followed by a colon as the new address.

Review all the changes proposed by CoA. Make sure that there are no commands or words that end in "d:" that would be changed to an ending of "r:". This would cause the name of the command or word to change.

For example, one of the registry entries for Microsoft Graph is: Default Chart=Standard:1,4.

COA2 (Change of Address) ( GetIt By Neil J. Rubenking
Change of Address lets you change the addresses of 32-bit Windows programs by changing the references to its path in the Registry and .INI files. Basically it does a search and replace. Publication Date: May 8, 2001 (v20n09) in PC Magazine.

Unfortunately, ZDNet/PCMag requires a subscription to download their "free" software. But you can download it from PC Hardware and PC Software Help Links. o,4149,88432,00.asp

My original version of this tip was published in the December 16, 1997 (vol. 16 no. 22) issue of PC Magazine p. 293
You can check out Neil J. Rubenking's comments in Reserving a Letter for the CD-ROM Drive


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