Category : Alternate Operating Systems - Quarterdeck DesqView, CP/M, etc
Archive   : UNMAP.ZIP
Filename : UNMAP.PAT

 
Output of file : UNMAP.PAT contained in archive : UNMAP.ZIP
Quarterdeck Technical Note


Patching QEMM-386 6.00 and 6.01 to cause QEMM-386 not to unmap
free pages when an Expanded Memory (EMS) handle is freed.

Background: Beginning with version 6.00, QEMM-386 unmaps from the
page frame any pages of Expanded Memory that belong to an EMS
handle that is freed. It is possible that an EMS user may rely on
memory being left in the page frame even after it has surrendered
its EMS handle. Since QEMM-386 version 6 ensures that there is no
memory in the page frame after the program has freed its EMS
handle such a program malfunctions. QEMM-386 does this for a good
purpose: to allow the ROM underlying the page frame to be visible
whenever Expanded Memory is not being used. The drawback to not
unmapping free pages from the page frame is described below.
Quarterdeck considers it poor programming practice for a program
to use the page frame without taking out an EMS handle. If you
find that this patch makes your program work where it previously
failed you should report this to the author of the program. We at
Quarterdeck are willing to discuss this matter with the authors of
any commercial software that uses EMS in this manner.

Glyphix 3.1 (dated 12/26/90) is one program that needs this patch.

Drawbacks: If you are using QEMM-386's Stealth feature, this
patch may cause some users with SuperVGA cards to need to exclude
C000-C0FF (or some portion of the address space occupied by the
VGA ROM) to run high-resolution video modes. Before using the
patch, placing the page frame at C000 (the default location when
the ST:M option is in effect) should make such an exclusion
unnecessary.

The following procedure prevents QEMM-386 from unmapping free EMS
pages when an EMS handle is freed.

-------------------------------------------------

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\QEMMOLD.SYS

(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 the the DEBUG prompt, which is a
hyphen.

3) At the DEBUG prompt, type:

S 100 L FF00 3B E8 75

Hit the Enter key; DEBUG should return a segment address and
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 3B E8 EB

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 the key after the command; 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.

--------------------------------------------------

If the system fails after you perform this patch, copy the backup
of QEMM386 that you made back to its original name.

COPY C:\QEMM\QEMMOLD.SYS 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 * * *


  3 Responses to “Category : Alternate Operating Systems - Quarterdeck DesqView, CP/M, etc
Archive   : UNMAP.ZIP
Filename : UNMAP.PAT

  1. Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

  2. This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

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