ID:51 Disabling Motherboard Memory
Quarterdeck Technical Note #139
by Stan Young

                  DISABLING MOTHERBOARD MEMORY

Q:   Why can't I run more than 1 large program under DESQview on my
     AT clone.

Many AT "clone" systems do not allow the motherboard to be
configured with less then 512k of memory.  This is a difficult
problem for users who want to use an EEMS or EMS 4.0 memory board
to run multiple programs under DESQview.

The addition of an EEMS or EMS 4.0 expanded memory board will allow
DESQview to load portions of its code into memory addresses above
640K, resulting in a larger first partition.  To get this large
first partition does not require disabling memory on the
motherboard.  DESQview can then allow you to run more than 640K of
programs by swapping programs from the first partition to expanded
memory.  However, if you want to run concurrent or non-swappable
programs using expanded memory, DESQview must be able to map
expanded memory pages down into the lower 640K.  This is a function
of the EEMS or EMS 4.0 driver.  The limitation is that the EMS
driver can not map memory into an area in use by something else;
for example, your motherboard RAM.

The size of the partitions that will be available after the first
640K is used up is defined by the size of the area between the
installation address of the expanded memory board and the base
address of the video card.  Since an EGA card starts at a 640K
address, an IBM AT or other machine that can set up the expanded
memory card at 256K will get a 384K expanded memory partition,
while a "clone" that can only set the motherboard to 512K gets a
128K partition.  Even on IBM machines, sometimes this partition is
not as large as one might desire.

There is nothing that software can do to rectify this restriction.
This is a hardware issue, based on the way expanded memory hardware
works.

Q:   So, what do you do if you have a machine that can only set
     motherboard memory to 512K?

First, you should consult with the manufacturer's support personnel
to see if this is really the case.  Many times there may be a way
to set up the machine, even though not documented in the manual.
Additionally, some manufacturers may have a new ROM or PAL chip
that permits setting up the motherboard at 256K or below.  It
should be noted that this is an issue of compatibility. "Clone"
machines that cannot set up the motherboard at 256K are certainly
not clones and are incompatible with the IBM machines at the
hardware level.  Given a high enough level of interest from users,
a manufacturer may develop a fix for the problem.
Second, you might consider migrating into a 386 based environment
through the installation of a 386 motherboard or addon processor
card. Since the 386 chip has such vastly superior memory
management, it is possible to do all of the memory management
necessary without special hardware.  On a 386 based machine,
exTENDed memory is used to emulate EMS 4.0 memory and expanded
memory pages can be set on the motherboard from 0K without
disabling any motherboard memory.  Additionally, there are other
benefits inherent to the 386 environment, such as extra speed and
reliability.

   Third, you might consider the addition of a 286 Memory
Management Unit (MMU), such as the All Computer's ChargeCard or
Sota Technologies SotaPop card, which provide a 286 machine with
some of the memory management capability that you would get from a
386.  As with a 386, when using an 286 MMU, memory management is
provided at the CPU level and expanded memory pages can be set on
the motherboard from 0K WITHOUT DISABLING ANY MOTHERBOARD MEMORY! 
While these cards do not increase speed or provide the virtual 86
mode of the 386, they do provide an avenue for obtaining a fully
functional EMS 4.0 system at a modest price.

        Copyright (C) 1991 by Quarterdeck Office Systems
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