VMS Help Sys Parameters, XQPCTLD1  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    XQPCTLD1 controls multithreading, which can be used only
    by PATHWORKS servers. The default value of XQPCTLD1 is 8,
    which enables multithreading. Setting XQPCTLD1 to 0 disables
    multithreading,

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