Path: utzoo!utgpu!news-server.csri.toronto.edu!torsqnt!lethe!druid!darcy
From: darcy@druid.uucp (D'Arcy J.M. Cain)
Newsgroups: comp.sys.ibm.pc.misc
Subject: Re: emm40.sys - expanded memory
Message-ID: <1990Aug18.131250.18988@druid.uucp>
Date: 18 Aug 90 13:12:50 GMT
References: <90228.143145RFM@psuvm.psu.edu> <1990Aug16.202610.28641@sun.soe.clarkson.edu>
Organization: D'Arcy Cain Consulting, West Hill, Ontario
Lines: 52

In article <1990Aug16.202610.28641@sun.soe.clarkson.edu> levericw@clutx.clarkson.edu writes:
>From article <90228.143145RFM@psuvm.psu.edu>, by <RFM@psuvm.psu.edu>:
>> Extended memory is different from expanded.... You can designate some
>> expanded memory to be treated as expanded, but you cannot go the
   ^^^^^^^^ <--- He means extended
>> other way--expanded to extended. Wish you could.... Bob M.
>
>I'm confused here, is not all memory above 1Mb exTENDed until you
>install an EMM device driver?  If so why would you want to go exPANDed
>to exTENDed, just make the driver allocate a smaller number of pages.
>

Sigh.

Why do people have to add unneccessary terms to the language.  OK, here
are the proper terms.

Extended memory -- memory | native memory | additional memory
Expanded memory -- Banked memory

Now think of the regular memory in an IBM-PC as "Partial memory."  Extended
memory is just add-on memory on systems with chips that can directly address
it.  The only thing "extended" about it is that IBM and Microsoft think
that the world ends at 1 megabyte.

Lotus, Intel and Microsoft invented a banked memory scheme (Hence LIM) which
was designed to get around the DOS 1 megabyte limit.  Now LIM memory was
designed to work in systems that could not address more than 1 megabyte.
Therefore, the only way to get more memory was to use a banked memory
scheme.  The physical memory is banked into an area of memory that can
be addressed directly by the 8088 or 8086 chip.

So the important point here is that the memory known as expanded is not
necessarily "above" the 1 megabyte line.  It may be within it.  The only
time it is above is when extended memory is used to emulate banked memory.
The EMS driver has the processor move a block from above 1 megabyte into
the space below so that DOS can see it.  Thus extended can emulate expanded
but if you have an expanded memory board (especially in a PC ot XT) you can
not use it as extended or native memory.  You must bank it in to native
memory to use it.

So why did Lotus/Intel/Microsoft invent the new names.  Are they trying
to make people think that they invented something new?  I can see them
siting around a table cackling over the fact that "extended" sounds so
much like "expanded" that they will be able to confuse the maximum number
of users with that terminology.

-- 
D'Arcy J.M. Cain (darcy@druid)     |
D'Arcy Cain Consulting             |   MS-DOS:  The Andrew Dice Clay
West Hill, Ontario, Canada         |   of operating systems.
+ 416 281 6094                     |