VMS Help SHOW, DEVICES, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 device-name[:]

    Specifies the name of a device for which information is to be
    displayed. The device name displayed by the system uses the
    format ddcu where dd is the device code, c is the controller
    designation, and u is the unit number. If the system is part
    of an OpenVMS Cluster that is running with HSC controllers, the
    device name must include the node name using the format node$ddcu
    (where node is the node name).

    You can specify a complete device name or only a portion of
    a device name. The SHOW DEVICES command provides defaults for
    nonspecified portions of device names, as follows:

    o  If you truncate a device name (for example, if you specify D),
       the command lists information about all devices whose device
       names begin with what you entered (in this case, D). However,
       if you specify a device in an OpenVMS Cluster that is running
       with HSC controllers, you must include the entire node portion
       of the device name.

    o  If you omit a controller designation, the SHOW DEVICES command
       lists all devices on all controllers with the specified unit
       number.

    o  If you omit a unit number, the SHOW DEVICES command lists all
       devices on the specified controller.

    Note that the /FILES qualifier does not support defaults for
    nonspecified portions of device names; you must supply a complete
    device specification.