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        Mode Switching


            There are  three different  ways a  client can  force a mode
            switch between protected and real mode:

                 o    Execute the default interrupt reflection handler
                 o    Use the  translation services  to call  real  mode
            code
                 o    Use a  real mode  call-back to switch from real to
            protected mode
                 o    Use the raw mode switch functions

            All mode switches except for the raw mode switches will save
            some information  on the  DPMI host's  ring 0  stack.   This
            means that  programs should  not terminate  while in  nested
            mode switches  unless they  are using the raw mode switching
            services.  However, even programs that use raw mode switches
            should not attempt to terminate from a hardware interrupt or
            exception handler  since the  DPMI host  performs  automatic
            mode and stack switching to provide these services.