Microsoft DOS mscdex command

Updated: 05/21/2018 by Computer Hope

About mscdex

Mscdex is a CD-ROM "redirector" that enables CD-ROM access from the MS-DOS.


The mscdex or mscdexnt commands are external commands that are available in the below versions of Microsoft operating systems as mscdex.exe or mscdexnt.exe.

Mscdex syntax

Syntax: MSCDEX.EXE /D:x /M:n /E /V /L:x /S /K

/D:Device name Allows you to specify the name for the driver. This device name must be identical to the device name in the config.sys file. Usually, MSCD0001 is commonly used.
/M:<n> Specifies the number of sector buffers to cache the path table of a CD-ROM disk. Typically, each drive should have four to five buffers. The larger this number is, the less your computer will read directly from the CD-ROM drive.
/E Tells MSCDEX.exe to use expanded memory.
/V Displays information on memory usage when you boot your PC.
/L:<drive letter> Specifies the drive letter you want to assign the first CD-ROM drive. Such as D:
/S Allows the CD-ROM to be shared on MS-NET based systems.
/K (Japanese) Tells MSCDEX.EXE to use any KANJI file structures if present rather than the default of alphanumeric file structures.

Extra Notes:

When loading the MSCDEX line in Windows 3.x, make sure to define the LASTDRIVE= statement with a line similar to "LASTDRIVE=Z" line.

Mscdex examples

Below is an example of how the MSCDEX line should look in your autoexec.bat:


Remember that the above example, if used, must have the same device driver name as the CD-ROM driver in the config.sys.

Errors and issues

When booting, I receive the message "MSCDEX is already running," and if I continue, all programs will stop running.

It is likely that you have more than one MSCDEX statement in your autoexec.bat. Edit the autoexec.bat and place a REM in front of one of the MSCDEX lines in the autoexec.bat.