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.
Note: If you do not need to access the CD-ROM drive from DOS, you can skip the following.
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.
e.g. DEVICEHIGH=C:\UT\DRIVERS\SCSI\ASPICD.SYS /D:MSCD001
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,
LOADHIGH C:\WINDOWS\COMMAND\MSCDEX.EXE /D:MSCD001 /L:R
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.
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.
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