How a CD-ROM Drive Letter Is Assigned (93234)

The information in this article applies to:
    Microsoft MS-DOS operating system 5.0
    Microsoft MS-DOS operating system 5.0a
    Microsoft MS-DOS operating system 6.0
    Microsoft MS-DOS operating system 6.2
    Microsoft MS-DOS operating system 6.21
    Microsoft MS-DOS operating system 6.22

This article was previously published under Q93234


The drive letter for a CD-ROM drive is assigned by the MSCDEX.EXE command in the AUTOEXEC.BAT file, not by the device specific driver in the CONFIG.SYS file. MSCDEX.EXE loads the Microsoft CD-ROM Extensions.


MSCDEX.EXE assigns a CD-ROM the next available drive letter. For example, if a computer has two floppy drives (drives A and B) and one physical hard drive with two partitions (drives C and D), then MSCDEX will assign the CD- ROM the drive letter E. It is possible to specify a drive letter to the CD- ROM by using a command line switch on the MSCDEX.EXE of /L:x, where x is the drive letter you want to assign. To assign a CD-ROM the drive letter H, you would use the following command:
When using a RAM Drive along with a CD-ROM, the RAM Drive will be assigned the first available drive letter, because RAMDRIVE.SYS (which loads in the CONFIG.SYS) is loaded before MSCDEX. The CD-ROM will then be assigned the second available drive letter.

Modification Type: Major Last Reviewed: 5/12/2003
Keywords: KB93234