igb@cunixa.cc.columbia.edu (Isidore G Bendrihem) (12/24/90)
I believe I've found a potentially dangerous compatibility problem between
QEMM 5.11 and the DOS 3.3 BACKUP command. I apologize if this has been
reported previously.
I have a 386sx clone based on the C & T NEATsx chip set with 4MB RAM,
a WD1006V-MM2 HD/FD controller, 1.2 and 1.44 MB floppies, and two hard
disks. The system runs under MS-DOS 3.30 (the problem also occurs
with PC-DOS 3.30), with QEMM 5.1 installed.
I first experienced the problem when I tried to use DOS BACKUP to backup
a large file to 360KB floppies for a friend. When he tried to restore the
file, he found all the floppies' FATs had been trashed beyond repair.
CHKDSK would report lost clusters on these floppies. To reuse them, they
had to be reformatted. To pinpoint the source to this problem, I streamlined
my autoexec.bat and config.sys to bare minimums. I found the culprit to be
using LOADHI in my autoexec.bat to load DOS BUFFERS in high RAM. When I
used BUFFERS= in my config.sys, BACKUP would work normally. I played around
with LOADHI by changing the numbers of buffers from 39 to over 100 in various
increments. It seems as when you go high enough (I tried 125 buffers!),
BACKUP begins to function normally. This threshold number might be different
for every machine! I first experienced the problem with buffers set to 49.
To duplicate the problem, follow this procedure:
1. Start with freshly formatted floppies (sometimes I couldn't duplicate
the problem with previuosly used backup floppies). Make sure you are
using LOADHI in your autoexec.bat to add DOS buffers. Start with a small
number (about 39).
2. Try to backup a small file (I experienced the problem with small (<1K)
and large (3MB) files) with your current setup. Run DIR and CHKDSK on the
floppies and see if they report any problems
3. If Step 2 yields good backups, repeat the procedure with a streamlined
config.sys and autoexec.bat, that is, remove all TSRs and other junk.
If you finally get BACKUP to trash your diskettes, try repeating the
procedure with a higher number of buffers until BACKUP works correctly.
It is important that you reformat your floppies after each try (see 1).
The problem occurred with 360KB and 1.44MB drives. I'd like to hear from
other people that have experienced this problem. It is possible that it
might be hardware related.
Isidore Bendrihem
igb@cunixa.cc.columbia.edu