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

    (VAX only) VECTOR_MARGIN establishes the time interval when
    the system checks the status of all vector consumers. The
    VECTOR_MARGIN parameter accepts an integer value between 1 and
    FFFFFFFF(16). This value represents a number of consecutive
    process quanta (as determined by the system parameter QUANTUM).
    If the process has not issued any vector instructions in the
    specified number of quanta, the system declares it a marginal
    vector consumer.

    The default value of the VECTOR_MARGIN parameter is 200 subscript
    10.

    VECTOR_MARGIN is a DYNAMIC parameter.