🚀 go-pugleaf

First let me make sure I understand your question:  On most modern mother
boards, any memory left over after the standard 640k base memory is assigned
can be configured in some combination of 3 different ways:

1) Extended Memory, which is in the 1 meg+ region of the address space of
   an AT class or higher computer.

2) Expanded (LIM spec) memory, which sits out by itself but has a kind of
   "movable window" that shows up in the under 1 meg address space.

3) Shadow RAM, Hi-Mem(?), etc, (I'm not too sure about the terms used here)
   This memory actually goes in the 640-1meg space, which is what I think
   you are talking about.  They serve 2 functions,  first (Shadow RAM) your
   machine may copy the contents from the slow ROMS that are in your machine
   during boot-up time and copy them to your much faster RAM.  This way your
   machine is accessing this fast RAM when it thinks it is accessing slow
   ROMs.  Second, there is a lot of blank spaces in the 640-1meg area that
   is between these blocks of ROM.  You can fill this with RAM then SOME
   programs that are designed to go look for it can use it.  It is popular
   to load TSRs in this space.  Also DOS extenders, Desqview & Windows
   seem to know how to put this to good use too.
D