Manual

where drive:\path specifies the DOS directory or the directory containing the file
MSCDEX.EXE.
Note: If your AUTOEXEC.BAT file loads a menu program such as DOSSHELL
or Windows, you have to add the above line to start your menu program.
Otherwise, MSCDEX will not have a chance to load before your menu
program begins.
The example above shows the default setting. The /D: switch indicates the device
name. It MUST be the same name as you specified by the /D: switch of
EXPCDI.EXE in your CONFIG.SYS file. The /M: switch indicates how much
memory to allocate for caching information on the CD-ROM. The default /M:4
caches 8KB.
For more information about the switches of MSCDEX, please type “help MSCDEX”
at the DOS prompt.
5. Now, reboot your computer to activate the CD-ROM drive.