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

 device-name

    Specifies the physical device name or logical name of the device
    on which the volume is to be mounted. For MOUNT/VIRTUAL, the
    device-name parameter supplies a name for the virtual device.

 file-name

    For MOUNT/VIRTUAL only, the file-name parameter gives the name of
    the file containing the image of the foreign volume.