Path: utzoo!attcan!uunet!husc6!cmcl2!rutgers!apple!bionet!agate!ucbvax!ucsfcgl!pixar!unicom!fried
From: fried@unicom.UUCP (Martin J Fried)
Newsgroups: comp.sys.ibm.pc
Subject: Re: extended vs. expanded
Message-ID: <404@unicom.UUCP>
Date: 24 Nov 88 17:52:34 GMT
References: <1717I78BC@CUNYVM> <1090@esunix.UUCP> <1970@hoqax.UUCP>
Reply-To: fried@unicom.UUCP (Martin J Fried)
Organization: Science Computer Center, MCC, Kentfield, CA
Lines: 29

In article <1970@hoqax.UUCP> twb@hoqax.UUCP (T.W. Beattie) writes:
>In article <1090@esunix.UUCP> bpendlet@esunix.UUCP (Bob Pendleton) writes:
>>From article <1717I78BC@CUNYVM>, by I78BC@CUNYVM.CUNY.EDU (Michael Polymenakos):
>>...difference between "extended" and "expanded" memory. Can someone
>>please explain it to me?
>
>
>I'll try.
>Extended memory is the 384K between 640K and 1M.
>Expanded memory is the RAM above 1M.

This is incorrect.  Extended memory is memory above 1M (640K to 1M is used
by video mainly, with some space for network cards or other system programs.
In fact, this is where most _expanded_ memory is mapped.  Expanded memory is
is a chunk of ram that can be logically mapped into lower memory a section at
at a time, where it can then be used by DOS (originally in 16K sections, up to
64K).  DOS can't use anything over 1M, so it can't use extended memory.

The expanded memory that is swapped into the lower address space acts like
a 64K window into the physical memory.  The physical memory can be any type
of memory that is capable of being addressed as DOS memory, and can be
accomplished in software only, although this is much slower than memory 
designed to be used as expanded memory.

Expanded memory can be used by XT or AT, where extended memory only exists
on the AT.

I hope my explanation is somewhat understandable.  I know I'm not the world's
greatest writer!