Segment to Descriptor


                 This function  is used  to convert  real mode  segments
                 into descriptors that are addressable by protected mode
                 programs.

            To Call

                 AX = 0002h
                 BX = Real mode segment address

            Returns


                 If function was successful:
                 Carry flag is clear.
                 AX = Selector mapped to real mode segment

                 If function was not successful:
                 Carry flag is set.

            Programmer's Notes

                 o    Multiple calls  to this  function  with  the  same
                      segment will return the same selector.
                 o    Descriptors created  by this function should never
                      be modified or freed.  For this reason, you should
                      use this  function sparingly.    If  your  program
                      needs to examine various real mode addresses using
                      the same selector you should allocate a descriptor
                      and change  the base  using the  Set Segment  Base
                      Address function instead of using this function.
                 o    The descriptor's limit will be set to 64K.
                 o    The intent  of this  function is to allow programs
                      easy access  to commonly  used real  mode segments
                      such as 40h and A000h.  Do not use this service to
                      obtain descriptors to private data areas.