VMS Help MOUNT, Qualifiers, /MEDIA_FORMAT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /MEDIA_FORMAT=CDROM

    Mounts a volume assuming the media to be ISO 9660 (or High
    Sierra) formatted.

    The /MEDIA_FORMAT=CDROM qualifier instructs the mount subsystem
    to attempt to mount a volume assuming the media to be ISO 9660
    (or High Sierra) formatted.

                                   NOTE

       This qualifier specifies a CD-ROM mount (ISO 9660 or High
       Sierra). Specify this qualifier when a volume is known to be
       in either ISO 9660 or High Sierra CD-ROM format.

       The Mount command attempts to read a CD-ROM in Files-11
       ODS-2 format by default. This qualifier prevents the Mount
       command from attempting a Files-11 ODS-2 mount sequence.

       Because it is possible to record parts of a CD-ROM in Files-
       11 ODS-2 and other parts in ISO 9660 format, this qualifier
       can be used to specify a CD-ROM mount (ISO 9660 or High
       Sierra).