PROBLEM - I Had 2 1.2mb 5.25 floppy drives installed in
                   my 386 system and wanted to add a CMS tape
                   backup system without giving up a floppy. I
                   could purchase an add on card but it seemed
                   high priced to me.

         SOLUTION - make a cable to switch the "B" drive connector
                   from the floppy to the tape drive. Anytime I'm
                   not using the tape drive I leave the switch set
                   to the floppy drive. When I get ready to backup
                   I switch to the tape. The cost was less than $10.

         DETAILS - There are 2 critical lines that require switching.
                   Thes are named Motor Enable B and Drive Select B
                   in the IBM Technical Reference manual. A Double
                   Pole Double Throw toggle switch switches these
                   lines between devices.

         CONTSTRUCTION -


  34 pin connector
   on controller                                     "B"     "B"   "A"
    -    10 motor enable A                            -       -     -
     | ----------------------------------------------| |-----| |---| |
     |   12 Drive select B                           | |     | |   | |
     | ---------------------------            -------| |  ---| |---| |
     |   14 Drive select A        |          |       | | |   | |   | |
     | ---------------------------)----------)-------| |-)---| |---| |
     |   16 Motor enable B        |          |       | | |   | |   | |
     |----------------------      |          |      -| | |  -| |---| |
     |                      |     |          |     | | | | | | |   | |
     |                      |     |          |     | | | | | | |   | |
    -                       |     |    ------      |  -  | |  -     -
                            |      -->             |     | |
                            |          ------------)-----  |
                            |                      |       |
                            |          ------------        |
                             ------->                      |
                                       --------------------

                                   DPDT Switch

         Excuse the art work, but I hope you can figure it out with
         this explanation. I made a cable with 3 34 pin disk connectors.
         pins 10-16 are twisted between the last two like a standard
         IBM type cable. Pins 12 and 16 are cut at a convenient point
         after they come off the controller and before each of the 2
         "B" drive connectors. take the wire and solder on an extension
         and run it to a Double Pole Double Throw Switch. Next run
         wires from each side of the switch to the short pieces of
         wire coming from the connectors where you previously cut.
         Solder the connections and I recommend using heat shrink
         tubing for insulation on each connection. Now run the cable
         to the Tape drive, to the "B" disk drive and then to the
         "A" disk drive. Mount the DPDT switch in a convenient place
         and you're set.

         I had 3 drive openings in my clone case so I mounted the tape
         drive on the bottom and the switch in a small hole drilled in
         the front panel next to the keyboard lock switch.

         A friend who had only 2 openings mounted the tape inboard
         and got a case for the floppy drives and just made the
         cable long enough to go external.