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

    CTLIMGLIM specifies the size of the default image I/O segment;
    that is channel table and initial buffer pool for image-related
    file and RMS I/O.

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