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XDV.TEC
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1990-10-08
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5KB
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108 lines
ID:X2 XDV.COM/DV.COM - vs - DV.EXE
Quarterdeck Technical Note
by Dan Sallitt
Q: Why does DESQview fail when I use XDV.COM or DV.COM but work
correctly when I use DV.EXE?
XDV.COM, which is usually renamed to DV.COM by the DESQview Install
program (before DESQview 2.26, the Install program did not automatically
perform this renaming, though Quarterdeck's documentation recommended that
it be done manually), is a loader that places bits of DESQview code in high
memory areas. It is useful on any system that has expanded memory, or on
any system that has extended memory and is using DESQview's QEXT.SYS
driver, or on any system using QEMM.SYS. If DESQview loads successfully
when started with the DV.EXE file but not when started with XDV.COM or
DV.COM, there are two likely possibilities:
1) The system's expanded memory manager (EMM) has allowed DESQview to place
a piece of its code in an area between 640K and 1024K (known as the
reserved memory area) that is already being used by hardware in the
system;
2) QEXT.SYS is conflicting with another program that is using the first 64K
of extended memory.
In the first case, one must determine which part of the area between
640K and 1024K is in conflict, then exclude it using the expanded memory
manager's parameters. If you know the hardware in the system, you should
consult the manuals (or the manufacturers) of the expansion boards in the
machine to determine the addresses that are being used for ROM extensions,
buffers, etc.
If your system is a 386 running QEMM-386, the QEMM.COM Accessed screen
(also available as the Manifest QEMM 386\Accessed screen) can provide
valuable hints about what areas of memory are in use. To use the Accessed
screen, remove the RAM parameter (if it is in use) from the QEMM line in
the CONFIG.SYS file, add the ON parameter, and reboot the machine. Any
area that the Accessed screen then shows as having been touched, but that
the QEMM Type screen shows as Mappable or Rammable, is a good candidate for
exclusion.
Failing this, you should use the /X parameter to DV.COM or XDV.COM to
exclude different areas of reserved memory, making the exclusions smaller
and smaller until the conflict is pinpointed. Like most memory managers,
DV.COM/XDV.COM takes hexadecimal addresses; in hexadecimal, the range
A000-FFFF represents the addresses between 640K and 1024K. Thus the
command line
XDV /X:A000-FFFF
prevents DESQview from putting its code anywhere between 640K and
1024K.
XDV /X:A000-CFFF
excludes the first half of this area, and
XDV /X:D000-FFFF
excludes the second half.
All the possible 16K areas that can be excluded on DV.COM/XDV.COM
are listed below.
A000-A3FF A400-A7FF A800-ABFF AC00-AFFF
B000-B3FF B400-B7FF B800-BBFF BC00-BFFF
C000-C3FF C400-C7FF C800-CBFF CC00-CFFF
D000-D3FF D400-D7FF D800-DBFF DC00-DFFF
E000-E3FF E400-E7FF E800-EBFF EC00-EFFF
F000-F3FF F400-F7FF F800-FBFF FC00-FFFF
To exclude a number of these consecutive ranges, use the endpoints of
the first and last block that you want to exclude. For instance:
XDV /X:A000-ABFF
excludes the first three 16K areas above 640K.
To determine if QEXT.SYS is in conflict with anything in the system, use
this special exclusion on DV.COM or XDV.COM:
XDV /X:FFFE
Since the Quarterdeck Expanded Memory Manager-386 (QEMM-386) and other
expanded memory managers for 80386 machines allow DESQview to place code in
the QEXT area without the actual presence of the QEXT.SYS driver, this
exclusion should be tried when troubleshooting 80386 machines in general.
If the /X:FFFE exclusion eliminates the problem, look in the CONFIG.SYS
and AUTOEXEC.BAT files for drivers or terminate-and- stay-resident programs
that may be using extended memory. If a program is in conflict with
QEXT.SYS, the program may take parameters that will prevent it from using
the addresses between 1024K and 1088K, which QEXT.SYS must use.
It sometimes happens that a problem with XDV.COM or DV.COM is not
localized: that is to say, almost any use of the .COM files to put DESQview
code in almost any area causes the problem. In such cases, one should
probably look for a low-level conflict, usually on the hardware level. One
situation of this sort occurs on 80286 (or lower) systems on which an
expanded memory board is used to backfill motherboard memory without the
user having disconnected the already existing motherboard memory. The
resulting address conflict causes immediate crashes with DV.COM or XDV.COM;
DV.EXE will also crash in this circumstance, but not until DESQview has to
allocate expanded memory to open multiple windows.
Copyright (C) 1990 by Quarterdeck Office Systems
* * * E N D O F F I L E * * *