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

    input-specifier

    Specifies the input for the BACKUP operation as either a file
    specification, a BACKUP save-set specification, or a device name.
    If the input specifier is a save-set specification on disk, you
    must include the input save-set qualifier /SAVE_SET.

    You can specify DECnet node names in save-set specifications
    only. You can use wildcards characters in file specifications,
    and in save-set specifications if they are on magnetic tape.

    output-specifier

    Specifies the output for the BACKUP operation. The output
    specifier, like the input specifier, can be either a file
    specification, a BACKUP save-set specification, or a device name.
    If the output specifier is a save-set specification on disk, you
    must include the output save-set qualifier /SAVE_SET.

    You can specify DECnet node names in save-set specifications
    only. You can use wildcard characters when the output specifier
    is a Files-11 volume, but not when the output specifier
    is a BACKUP save-set specifier or a volume created by a
    BACKUP/PHYSICAL or BACKUP/IMAGE operation.