Category : Alternate Operating Systems - Quarterdeck DesqView, CP/M, etc
Archive   : QWAUG92.ZIP
Filename : 512AT.TEC

Output of file : 512AT.TEC contained in archive : QWAUG92.ZIP

ID:51 Disabling Motherboard Memory
Quarterdeck Technical Note #139
by Stan Young
last revision: 10 February 1992


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 cannot 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 or
VGA 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 add-on 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
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.

*This technical note may be copied and distributed freely as long as it*
*is distributed in its entirety and it is not distributed for profit. *
* Copyright (C) 1990-2 by Quarterdeck Office Systems *
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