6/28/85

Interaction between CED (a public-domain DOS command editor) and several
datafile PATH programs can cause multitasking systems to crash and likely
create problems with other combinations of system add-ons. The symptoms
we experienced were error messages like "MEMORY ALLOCATION ERROR, UNABLE
TO LOAD COMMAND.COM, SYSTEM HALTED". Then the system comes to a dead halt.

We were unable to test all possible combinations of interactions and do
not know where the cause may lie. This document is being distributed in
hopes someone else may benefit or, better yet, someone may find a way to
make all these programs co-exist.
 
Here is the decision table describing what worked together and what didn't:

		DPATH30  |    FILEFAC
---------------------------------------
CED10C	   |	  NO	 |	 NO
	   |---------------------------
RETRIEVE   |	  NO	 |	YES
	   |---------------------------
DOSEDIT    |	 YES	 |	YES
---------------------------------------

It's odd that RETRIEVE didn't work with DPATH30 but I can't explain it.
Of course it's possible that any of the combinations might fail under
slightly different circumstances but DOSEDIT and FILEFAC had been in use
for about six months without the error having occured.

Background: The programs heading the columns are both extensions of
the PATH concept to search for data files at OPEN time. DPATH30 is
public domain and FILEFAC is from IBM in the "Personally Developed
Software" series ($20). The programs in the left column (heading the
rows) are all command editors for the DOS command line. They also
keep a circular buffer of past commands issued from the console so
you can retrieve some prior command, edit it in place, and reissue it.
CED10 is public-domain (this is the last such release), RETRIEVE is
from the same IBM low-cost software series as FILEFAC (in Utilities I,
$20), and DOSEDIT is an earlier version of RETRIEVE that was "released"
to the public-domain and then "withdrawn" from P-D when IBM decided to
make it a product.

Specifics:  My experience with MultiLink and DOS 2.1 had been quite good
and I had used DOSEDIT and FILEFAC quite successfully with it when the
two public-domain equivalents were released. So I decided to switch.
Then the system started crashing when even trivial programs were run in
the "middle" partition of a three partition MultiLink setup. Here's the
layout - it's a 640k PC running DOS 2.1:

VDISK	192k (Version 2.0 RAMDISK)
FG	140k
BG1	128k
BG2	 96k

The tests were made by loading up the system and trying to run SD.COM
in BG2. No changes were made to the AUTOEXE?.BAT files except maybe the
names of the programs to be run. In most cases, no changes were made to
the BATs at all. Instead, I renamed the programs to match the BAT and
re-booted the system.

The BAT files looked essentially like so:

ECHO ON 			       A
VERIFY ON			       U
PATH C:\;C:\CMDS;C:\RBBS;C:\1;C:\PT    T
BUF128				       O
DOSEDIT 			       E
MLSLICE 			       X
MLINK /9,128/9,96		       E
ASSIGN B=F			       C
PROMPT $P$G			       .
SET FF=C:\RBBS;C:\1;C:\ 	       B
FILEFAC /I			       A
MLUTIL DIS			       T

ECHO ON 			       A
BREAK OFF			       U
VERIFY ON			       T
PROMPT $P$G			       O
PATH C:\;C:\CMDS;C:\RBBS;C:\1	       E
SET FF=C:\;C:\1 		       X
FILEFAC /I			       E
MLUTIL DIS			       1

ECHO ON 			       A
BREAK OFF			       U
VERIFY ON			       T
VERIFY				       O
PROMPT $P$G			       E
PATH C:\;C:\CMDS;C:\RBBS;C:\1	       X
FILEFAC /I			       E
MLUTIL DIS			       2

Similar system failures were seen when CED10C and DPATH30 were together
on DOS 3.1 running under Multijob 2.80H. However, all combinations were
not run to verify that the decision table was identical. The Multijob
configuration was a 512k PC/AT running only two partitions. The failures
occured in partition two.

Incidentally, BUF128.COM works fine with MultiLink 2.x but not with
Multijob 2.80H. Is there a buffer expander that's compatible with Multijob?

We shouldn't expect too many DOS "enhancements" to work together because
they steal interrupts from one another and otherwise violate rules about
coding for DOS. I doubt that interrupt stealing is the cause but if there
is a bug in CED, the console input routine could be buggered. By the way,
if you haven't tried this combination of three enhancements, you should.
These three functions, (multi-tasking, file path, and command-line editor),
are probably the three most important add-ons when it comes to improving
the productivity of DOS. Once you get used to them you will wonder how you
ever did without them. And if you are coming from CP/M, you will be a PC-DOS
convert forever.
 
Anyone with ideas on what these problem(s) is/are is cordially invited
to leave a comment to the sysop of Dallas RBBS-PC at (214) 931-8073. I
wish I could offer the source code for these programs but all that has been
made public is the ASM for a prior release of DPATH.

Dave Crane
Sysop, Dallas RBBS-PC
ese programs but all that has been
made public is the ASM fo