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1 definition found
 for extended memory
From The Free On-line Dictionary of Computing (30 December 2018) :

  extended memory
  
      Memory above the first megabyte of address space
     in an IBM PC with an 80286 or later processor.
  
     Extended memory is not directly available in real mode, only
     through EMS, UMB, XMS, or HMA; only applications
     executing in protected mode can use extended memory
     directly.  In this case, the extended memory is provided by a
     supervising protected-mode operating system such as
     Microsoft Windows.  The processor makes this memory
     available through a system of global descriptor tables and
     local descriptor tables.  The memory is "protected" in the
     sense that memory assigned a local descriptor cannot be
     accessed by another program without causing a hardware trap.
     This prevents programs running in protected mode from
     interfering with each other's memory.
  
     A protected-mode operating system such as Windows can also
     run real-mode programs and provide expanded memory to
     them.  DOS Protected Mode Interface is Microsoft's
     prescribed method for an MS-DOS program to access extended
     memory under a multitasking environment.
  
     Having extended memory does not necessarily mean that you have
     more than one megabyte of memory since the reserved memory
     area may be partially empty.  In fact, if your 386 or higher
     uses extended memory as expanded memory then that part is not
     in excess of 1Mb.
  
     See also conventional memory.
  
     (1996-01-10)
  

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