VMS Help EXCHANGE, INITIALIZE, Qualifiers, /SEGMENTS  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /SEGMENTS=n

    Defines, for RT-11 volumes, the number of 2-block directory
    segments to allocate for the directory. The number of segments
    in the directory establishes the number of files that can be
    stored on a device. The system allows a maximum of 72 files
    per directory segment and 31 directory segments per device. The
    argument n represents the number of segments; the valid range for
    n is from 1 to 31 (decimal). The default values for n depend on
    the device type, as follows:

    Device    Segments

    TU58      1
    RX01      1
    RX02      1 (single density)
    RX02      4 (double density)
    RX50      4
    RX33      16
    RL02      16
    RK06      16
    RK07      31