Extended memory is not directly available in
real mode, only
directly. In this case, the extended memory is provided by a
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.
prescribed method for an
MS-DOS program to access extended
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.
(1996-01-10)