Automating drive mounting in DosBox, is a must for many of its users, and that's where the Option file comes in. You will find a shortcut for the options file in the start menu, after installing DosBox.
To automatically mount a drive when starting DosBox, open up the Options file, and scroll all the way to the bottom of the file, add your own commands in the [autoexec] section of the file. To automatically mount a directory as your c drive, and d as the CD-ROM drive, the section should look like:
[autoexec] # Lines in this section will be run at startup. # You can put your MOUNT lines here. MOUNT D M:\ -t cdrom MOUNT C C:\DOSC
The MOUNT command is used for mounting, the letter represents the drive letter that you want to assign to whatever it is you are mounting.
The -t cdrom part will mount as CD-ROM, other options include: dir (default) and floppy, note that dir is left out of the last command, since its already default.
MOUNT C C:\DOSC
Hence the -t parameter simply changes the mount type.