/sys$common/syshlp/helplib.hlb Sys Parameters, EXUSRSTK  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    EXUSRSTK specifies the amount of space provided by the image
    activator to recover from a stack overflow error.

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