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[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting Specific Components | Troubleshooting CD-ROM Drives | Configuration Problems ]

The drive letter assigned to my CD-ROM drive keeps changing, which makes my installed programs not work properly

Explanation: The CD-ROM drive you use in your system is using a specific drive letter. Under certain circumstances (notably when changing hardware configurations such as adding a hard disk or using a removable drive) the letter associated with the CD-ROM changes. So the CD-ROM may be D: in some cases but E: after a change. This causes installed software to stop functioning since it looks for the information on the CD using the D: path when the drive is now on E:.

Diagnosis: CD-ROM drives are mapped to a drive letter using the driver software that enables them to function. This is done by the DOS program MSCDEX if you are using DOS or Windows 3.x, or a built-in CD-ROM file extension program if you are using Windows 95 or NT. By default, the CD-ROM drive takes the next unused drive letter available on the system, after all hard disk volumes are assigned letters. If you add a hard disk or change the partitioning to add another disk volume, or if you add a removable drive whose drivers load before the CD-ROM's, the CD-ROM's letter will be bumped up to the next letter.


  • The best solution is to set MSCDEX or Windows so that they use a specified, higher drive letter that is away from the other letters used for hard disks and allows for some expansion. This way you can add other devices and the CD-ROM's drive letter won't change. I personally use J: for my CD-ROM; you could use L: or R: or whatever you like.

Warning: Check your CONFIG.SYS file to make sure there is no "LASTDRIVE" command there before setting a high drive letter, as this can cause a problem by telling your system not to use high drive letters. Also watch out for mapped network drives if you are on a network, since they too may use high drive letters.

  • If you are using MSCDEX in your AUTOEXEC.BAT, try putting the MSCDEX command at the top of the AUTOEXEC.BAT file. Use the parameter "/L:<x>" to specify the drive letter you want to use, for example "/L:J". Load other storage drivers after MSCDEX so they take drive letters after the CD-ROM drive.

Note: Windows 3.x systems access the CD-ROM drive using MSCDEX so the instructions above apply to these machines.

  • If you are using Windows 95, you can change the drive letter by accessing the CD-ROM's properties under the Device Manager.
  • Any existing programs that have already been installed and aren't working due to the change in drive letter will have to be changed. Usually they can be changed by looking for an .INI file in their directory that contains a drive-letter reference. You may need to reinstall the program.
  • When installing Windows 95, do the MSCDEX drive letter change when first setting up the CD-ROM in DOS. This way Windows will install from the CD using the right drive letter and will be able to find the Windows CD in the future when you need to update drivers or whatnot.

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