/sys$common/syshlp/helplib.hlb SET, MAGTAPE, Qualifiers, /DENSITY  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /DENSITY=density-value

    Specifies the default density for all write operations on the
    magnetic tape device when the volume is mounted as a foreign tape
    or as an unlabeled tape.

    Valid density values are:

    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 keywords above are understood by TMSCP/TUDRIVER
        code prior to OpenVMS Version 7.2. The remaining keywords
            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