MULTIPLE_KERNEL_THREADS

    On x86, I64 and Alpha systems, this keyword sets the
    MULTIPLE_KERNEL_THREADS bit in the dynamic segment (x86 and
    I64) or the image header (Alpha) of the image being built. This
    bit indicates to the image activator that the image can be run
    in a multiple kernel threads environment.

    If you specify this keyword for OpenVMS VAX links, it is ignored.

 UPCALLS

    This qualifier sets the UPCALLS bit in the OpenVMS dynamic segment
    (x86 and I64) or image header (Alpha and VAX) of the image being
    built. This bit indicates to the image activator that the process
    can receive upcalls from the OpenVMS scheduler.

    When the /THREADS_ENABLE qualifier is specified without either
    the MULTIPLE_KERNEL_THREADS or UPCALLS keyword, the linker sets
    both bits by default.