ID:EP Expanded Memory Boards: Which Board is Best?
Quarterdeck Technical Note #149 Filename: EXPAND.TEC
by Dan Sweeney CompuServe: EXPAND.TEC
Last revised: 2/12/92 Category: HW3
Subject: Questions to ask and features to look for when purchasing an expanded
Q: WHICH EXPANDED MEMORY CARD SHOULD I BUY?
The type of ExPANDed memory card recommended for use with DESQview
depends on the motherboard configuration of your computer. The ability to
disable motherboard memory, and the amount of memory that can be disabled, are
This discussion assumes that the motherboard memory can be disabled to a
minimum of 256K. If your computer's motherboard memory can't be disabled
below 512K, then skip to the Other Choices section.
CAN THE BOARD MAP MEMORY BELOW 1024K?
In all cases the memory card should be able to map memory below 1024K.
Many exPANDed memory boards can map 64K (four 16K pages - usually known as the
page frame) below 1024K but not below 640K. These boards' hardware supports
the EMS 3.2 memory specification. (Adding an EMS 4.0 driver doesn't allow
them to map memory below 640K. This requires hardware as well as the software
CAN THE BOARD MAP MEMORY BELOW 640K?
The most desirable feature of an exPANDed memory board on a DESQview
system is the ability to map memory below 640K. Some boards can map memory
down to 0K.... provided your motherboard memory can be totally disabled. This
property should not be confused with backfilling motherboard memory.
Backfilling motherboard memory simply fills your DOS program memory area back
up to 640K. The ability to map memory to the area between 0 and 640K is
MANDATORY for multitasking of large programs.
DOES THE BOARD HAVE ALTERNATE PAGE MAPPING REGISTERS?
ExPANDed memory is allocated in 16K blocks called pages. When DESQview
opens applications it instructs the memory manager to allocate enough of these
pages (which may not be physically contiguous) and make them appear contiguous
and map them below 640K. When you switch among applications the memory
manager has to sort through all these 16K pages, find the correct ones, and
map them into the area below 640K. This can take a long time to do for a
large memory are. The delay may not be apparent to you unless you're running
communications in the background. If the memory card supports alternate page
maps, DESQview can instruct the memory driver to save the necessary
information to an alternate page map register (again this is hardware, managed
by a software driver). When you switch windows, DESQview instructs the
memory driver to call the page map rather than sort through all the expanded
memory. This is very important if you need to run high speed communications in
background, or have several large applications running simultaneously. Large
numbers of alternate page mapping registers on the board result in better
multitasking performance when running several programs at once. DESQview uses
one of these maps for itself, and one for each window open.
WHERE CAN I FIND OUT ABOUT EXPANDED MEMORY CARDS?
The technote "EMSCOMP.TEC" contains a comparison of the features of many
Expanded memory cards. You can fax yourself this technote from Quarterdeck's
QFAX fax-back service (310-314-3214). It is number 235. You can download it
from the Quarterdeck BBS (310-314-3227), or get it from Compuserve, Genie, or
Obtain a copy of InfoWorld's December 12, 1988 issue or PC Magazine
Volume 8, Issue 21 (December 12, 1989) issue (page 169). Both articles give a
very detailed comparison of ExPANDed memory boards. Most exPANDed memory card
manufacturers and their boards are listed. Call InfoWorld at (415) 328-4602
or PC Magazine at (212) 503-5255 for information on obtaining reprints.
If you have an 80286 based computer but cannot disable motherboard
memory, there are two options available. The first is a memory management
unit like the All Computers CHARGECARD or the Sota POP card. While these
devices contain no memory, they in fact have the ability to convert ALL the
conventional and exTENDed memory on an 80286 based machine into ExPANDed
The second option is to convert the computer to an 80386.
IS A 386 BETTER FOR MULTITASKING?
YES!!!!!! An 80386 is not only faster than the 8088 and 80286 based
computers (speed is only one of its many virtues). It is incredibly more
intelligent! It has the capability to run in virtual 8086 mode. Used in
conjunction with QEMM-386, a 386 requires no special memory cards, and no
motherboard memory needs to be disabled. The 80386 can allow QEMM to remap
all exTENDed memory into exPANDed memory. DESQview-386 can run bit-mapped
graphics programs like Ventura Publisher, AutoCAD, GEM, etc. in small windows
in the background. In addition, DOS Extended programs like Lotus 1-2-3
Release 3 and AutoCAD 386 that use the VCPI (Virtual Control Program
Interface) can co-exist with other programs that use exPANDed memory. Memory
protection is available in DESQview-386 for ill-behaved programs. These
capabilities are not available on 8088 or 80286 computers. If you're
considering this option and have the means (money), don't hesitate for a
*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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