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        Descriptor Management


            Protected mode  code segments  can not  be modified.    This
            requires programs  to allocate  an alias  data descriptor if
            they need to store data in a code segment.

            Segment arithmetic  that works in real mode does not work in
            protected mode.

            Some calls will return a range of descriptors.  For example,
            if a  16-bit mode program allocates a block of memory larger
            than  64K,   the  call  will  allocate  several,  contiguous
            descriptors.   Each descriptor  will have a 64K limit except
            for the  final descriptor  which  will  have  a  limit  that
            contains the  remainder of  the block.  The call will return
            the first  selector in  the array.    To  get  to  the  next
            selector, your  program must  add the  value returned by Int
            31h call 0003h.