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INSTANCE.PAT
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1991-08-12
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Quarterdeck Technical Note
Subject: Patching QEMM-386 5.10, 5.11, 5.12 and 5.13
to withhold available Upper Memory Blocks from programs
running inside Microsoft Windows 3.0 enhanced mode.
Background: QEMM versions 5.10 through 5.13 take
advantage of Microsoft Windows 3.0's VXD interface to
provide a copy of all available Upper Memory Blocks
(identified by the QEMM.COM and Manifest utilities as
High RAM) to each window running inside Windows
enhanced mode. This seemed like a good idea at the
time: each window in Windows enhanced can load its own
set of programs into upper memory, either through the
XMS (Extended Memory Specification) or with QEMM-386's
LOADHI.COM program, when QEMM-386 is providing this
feature. However, few programs avail themselves of
this opportunity. Furthermore, the additional overhead
of providing a copy of all available UMB's for each
window places a memory strain on low-memory systems;
and, because Windows enhanced mode takes this overhead
out of conventional memory, the size of each window in
Windows enhanced mode shrinks, a high price for large
DOS applications to pay. Finally, Quarterdeck observes
that Windows enhanced mode may begin to malfunction if
QEMM-386 provides it with enough data to manage on a
window-by-window basis.
Versions of QEMM-386 after version 5.13 will not
provide a copy of available UMB's to each window in
Windows enhanced mode. In the meantime, QEMM-386 can
be patched to eliminate this feature.
This procedure is for use with the following QEMM-386
versions:
5.10
5.11
5.12
5.13
***************************************************
1) Make a copy of the QEMM386.SYS file in your
QEMM directory. We are about to alter your current
copy of QEMM386.SYS; the copy you make will serve as a
backup in case this operation fails.
COPY C:\QEMM\QEMM386.SYS C:\QEMM\QEMM386.OLD
(If your QEMM386.SYS is not located in the QEMM
directory of the C: drive, change the path
accordingly.)
2) Go to the DOS directory on the hard disk and
type:
DEBUG C:\QEMM\QEMM386.SYS
(If your QEMM386.SYS is not located in the QEMM
directory of the C: drive, change the path
accordingly.)
Hit the Enter key; you should see the DEBUG prompt,
which is a hyphen.
3) At the DEBUG prompt, type:
S 8000 L 2000 55 8B E9 BE
Hit the Enter key; DEBUG should return a segment
address and an offset:
xxxx:yyyy
4) At the DEBUG prompt again, use the segment address
and offset that was just returned to give the DEBUG
command:
E xxxx:yyyy EB 8
The address that DEBUG returned in step 3 should be
used in place of the address xxxx:yyyy, which we use as
an example. Hit the Enter key; the DEBUG prompt should
return in a moment.
5) At the DEBUG prompt, type
W
Hit the Enter key; DEBUG will announce that it is
writing a certain number of bytes, then it will return
the DEBUG prompt.
6) At the DEBUG prompt, type
Q
Hit the Enter key to exit DEBUG and return to DOS.
7) To double-check your patch, type the following
from the DOS prompt in your DOS directory:
COMP C:\QEMM\QEMM386.SYS C:\QEMM\QEMM386.OLD
(If your QEMM386.SYS is not located in the QEMM
directory of the C: drive, change the path
accordingly.)
Hit the Enter key. COMP should return:
C:QEMM386.SYS and C:QEMM386.OLD
Compare error at OFFSET x
File 1 = EB
File 2 = 55
Compare error at OFFSET x
File 1 = 08
File 2 = 8B
Eof mark not found
Compare more files (Y/N) ?
The value x after OFFSET will vary from version to
version of QEMM 5.1, but the rest of the message should
be the same: it tells us that there are exactly two
bytes difference between the files, and the differing
bytes are EB and 55 in QEMM386.SYS and 08 and 8B in
QEMM386.OLD. If COMP returns the message:
Files compare ok
...then you probably failed to use DEBUG's W command to
save your change, or you have compared the wrong files.
If COMP returns more than two compare errors, or if the
bytes returned by the compare errors don't match those
in the above example, the procedure has failed. In this
case, use the DOS command:
COPY C:\QEMM\QEMM386.OLD C:\QEMM\QEMM386.SYS
... to restore the original file, and try again.
If the patch was successful, you should now reboot the
system and test the patched version of QEMM-386.
--------------------------------------------------
If the system fails after you perform this patch, you
can follow the instructions in the "Installation"
section of your QEMM-386 manual to recover without
resorting to a boot floppy. After your system is
booted successfully, copy the backup of QEMM-386 that
you made back to its original name with the following
DOS command:
COPY C:\QEMM\QEMM386.OLD C:\QEMM\QEMM386.SYS
(If your QEMM386.SYS is not located in the QEMM
directory of the C: drive, change the path
accordingly.)
You may then wish to try the above procedure again, in
case a mistake was made.
* * * E N D O F F I L E * * *