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

    MPW_PRIO sets the priority of I/O transfers initiated by the
    modified page writer. The maximum value is 31, the minimum is 0,
    and the default is 4.

    This special parameter is used by Compaq and is subject to
    change. Do not change this parameter unless Compaq recommends
    that you do so.