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        Mark Real Mode Region as Pageable


                 Under some  implementations  of  DPMI,  all  memory  in
                 virtual 8086 mode is locked by default.  If a protected
                 mode program  is using  memory in the first megabyte of
                 address space,  it is  a good idea to use this function
                 to turn  off automatic  page  locking  for  regions  of
                 memory that will not be touched at interrupt time.

                 Do not  mark memory as pageable in regions that are not
                 owned by your application.  For example, you should not
                 mark all free DOS memory as pageable since it may cause
                 a page  fault to  occur while  inside of DOS (causing a
                 crash).   Also, do  not mark the DPMI host data area as
                 pageable.

                 It is  very important  to relock  any real  mode memory
                 using function  0603h  before  terminating  a  program.
                 Memory  that  remains  unlocked  after  a  program  has
                 terminated could result in fatal page faults when other
                 software is executed in that address space.

                 Note that  address space  marked as  pageable  by  this
                 function can  be locked  using function  0600h.    This
                 function is  just an  advisory service  to allow memory
                 that does  not need to be locked to be paged out.  This
                 function just  disables any  automatic locking  of real
                 mode memory performed by the DPMI host.

            To Call

                 AX = 0602h
                 BX:CX =  Starting linear  address of  memory to mark as
                      pageable
                 SI:DI = Size of region to page in bytes

            Returns

                 If function was successful:
                 Carry flag is clear.

                 If function was not successful:
                 Carry flag is set.

            Programmer's Notes

                 o    If this  function fails  then none  of the  memory
                      will be unlocked.
                 o    If the specified region overlaps part of a page at
                      the beginning  or end  of the  region, the page(s)
                      will be not be marked as pageable.
                 o    When  your   program  terminates  it  should  call
                      function 0603h to relock the memory region.
                 o    Unlike the  lock and unlock calls, the pageability
                      of the  real mode region is maintained as a binary
                      state, not  a count.   Therefore, do not call this
                      function multiple times for a given linear region.