DISKCOPY and DISKCOMP PATCHES FOR LARGE MEMORY MACHINES
In PC's with more than 320K free memory available as buffer
storage for the Diskcopy and Diskcomp routines, the IBM DOS
supplied programs will fail.  The programs apparently do not
check for valid track and sector values and will continue to
step past track 39 if memory is available even if there are
no more valid tracks.  The head will be banged against the
stops and read errors will be reported for track 40, sector 0,
etc. until the operator interrupts or memory has been filled.
The patches were obtained with the help of Dan Gregorio of
the downtown Houston IBM Products Center.  After several calls
to Boca Raton, we received these patches which seem to work
properly.
The reader should read over the DEBUG section of their DOS
manuals before beginning any of these procedures if they are
not familiar with the debugger.  Be sure to make backup copies
of Diskcopy.com and Diskcomp.com before starting.
DISKCOPY PATCH
 1.  Run the debugger on diskcopy by entering "debug diskcopy.com"
 2.  The debugger will respond with the hyphen prompt.
 3.  Type "e861 <return>"
 4.  The debugger will respond with something like "04B5: A2._"
     (note that "_" designates the cursor).
 5.  Carefully type the following "e8 <space> 74 <space> 00 <return>"
 6.  Type "e8d8 <return>"
 7.  Carefully type the following:
          3d <space>
          51 <space>
          00 <space>
          72 <space>
          02 <space>
          b0 <space>
          50 <space>
          a2 <space>
          36 <space>
          05 <space>
          c3 <return>
 8.  At the hyphen prompt, type "rcx <return>"
 9.  The debugger will respond with ":07D8"
10.  At the colon prompt, type "7e3 <return>"
11.  At the hyphen prompt, type "w <return>"
12.  At the hyphen prompt, type "q <return>"
13.  You should now be back in DOS and have the "A>" prompt.
DISKCOMP PATCH
 1.  Run the debugger on diskcomp by entering "debug diskcomp.com"
 2.  At the hyphen prompt, type "e6ec <return>"
 3.  Carefully type the following:  "e8 <space> 79 <space> 00 <return>"
 4.  At the hyphen prompt, type "e768 <return>"
 5.  Carefully type the following:
         3d <space>
         51 <space>
         00 <space>
         72 <space>
         02 <space>
         b0 <space>
         50 <space>
         a2 <space>
         95 <space>
         04 <space>
         c3 <return>
 6.  At the hyphen prompt, type "rcx <return>"
 7.  The debugger should respond with ":0668"
 8.  At the colon prompt, type "673 <return>"
 9.  At the hyphen prompt, type "w <return>"
10.  At the hyphen prompt, type "q <return>"
11.  You should now be back in DOS with an "A>" prompt.
Please note that the two procedures are very similar but are
different.  While we are using the patched routines without any
problems on both large and small memory machines, I cannot
accept any responsibility for the use of these patches.  
THEREFORE, THE USER IS WARNED THAT HE IS MAKING THESE PATCHES
AT HIS OWN RISK.  THE AUTHOR IS NOT RESPONSIBLE FOR ANY LOSS OF
DATA OR ANY OTHER PROBLEM THAT MAY RESULT FROM THE USE OF THE
INFORMATION PRESENTED HEREIN.
Please address comments to:
                 
                   Mitchell D. Garnett
                   72345,470
                   DIGITAL ENGINEERING GROUP, INC.
                   11999 Katy Fwy., Suite 150
                   Houston, TX 77079
                   (713) 531-6100