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

    (VAX only) SPTREQ sets the number of system page table (SPT)
    entries required for mapping the following components:

       Executive image
       RMS image
       SYSMSG.EXE file
       Multiport memory structures
       Each MASSBUS adapter
       Each UNIBUS adapter
       Each DR32 adapter

    The number of system page table entries required for all other
    purposes is automatically computed and added to the value of
    SPTREQ to yield the actual size of the system page table.

    SPTREQ is an AUTOGEN parameter.