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

       /DENSITY=N

    Output Save-Set Qualifier

    Specifies the recording density of the output magnetic tape. Use
    a value that is supported by the magnetic tape drive.

    If you do not specify the /DENSITY qualifier, the default density
    is the current density of the magnetic tape drive. You must
    specify the output save-set qualifier /REWIND with /DENSITY.

    The densities supported for tapes are shown in the following
    table.

    Table 1 Keywords for Tapes

    Keyword        Meaning

    DEFAULT        Default density
    800            NRZI 800 bits per inch (BPI)
    1600           PE 1600 BPI
    6250           GRC 6250 BPI
    3480           IBM 3480 HPC 39872 BPI
    3490E          IBM 3480 compressed
    833            DLT TK50: 833 BPI
    TK50           DLT TK50: 833 BPI
    TK70           DLT TK70: 1250 BPI
    6250           RV80 6250 BPI EQUIVALENT
          NOTE: Only the symbols listed above are understood by
     TMSCP/TUDRIVER code prior to OpenVMS Version 7.2. The remaining
        values in this table are supported only on Alpha systems.
    TK85           DLT Tx85: 10625 BPI-Cmpt III - Alpha only
    TK86           DLT Tx86: 10626 BPI-Cmpt III - Alpha only
    TK87           DLT Tx87: 62500 BPI-Cmpt III - Alpha only
    TK88           DLT Tx88: (Quantum 4000)-Cmpt IV - Alpha only
    TK89           DLT Tx89: (Quantum 7000)-Cmpt IV - Alpha only
    QIC            All QIC drives are drive-settable only - Alpha
                   only
    8200           Exa-Byte 8200 - Alpha only
    8500           Exa-Byte 8500 - Alpha only
    DDS1           Digital Data Storage 1-2G - Alpha only
    DDS2           Digital Data Storage 2-4G - Alpha only
    DDS3           Digital Data Storage 3-8-10G - Alpha only
    DDS4           Digital Data Storage 4 - Alpha only
    AIT1           Sony Advanced Intelligent Tapes - Alpha only

    The value that you specify must be supported by your magnetic
    tape hardware. If you omit this qualifier, the default density is
    the current density on the output tape drive.

    The /DENSITY qualifier is incompatible with the output save-
    set qualifier /NOREWIND. You must specify the output save-set
    qualifier /REWIND to initialize the magnetic tape when using
    the /DENSITY qualifier. When you specify /DENSITY/REWIND,
    BACKUP rewinds the tape to the beginning-of-tape. Then BACKUP
    initializes the tape with the new density, removing access to all
    data that previously resided on the tape.