June 12, 1987

      INSTALLING FOUR INTERNAL FLOPPY DRIVES IN AT-TYPE COMPUTERS.

   Compiled by Jim Gainsley [76703,1007] From Technical Information and
             Patches Provided By Clyde Washburn [70305,1211]
                           (CIS IBMHW Forum)

The PC/AT normally supports only two floppy drives. However, it is possible 
to have four internal floppies, (or two external AND two internal), and 
these may be any combination of the supported floppy drive types, e.g. 
160kb/360kb/720kb/1.2mb, and 1.4mb.  You will not need to change any of the 
controllers you have currently.

The following procedures may seem involved at first glance.  However, it's
one of those cases where it's more difficult to tell about than to 
accomplish.

Hardware/Software:

1) IBM's External Drive Adapter, p/n #2683198, which can be purchased 
   through any IBM Dealer. Price currently approximates $110. and will 
   fit in a short slot.  Note that this is a smart switch and not a
   controller.

2) A normal 34-pin two-floppy drive cable, except that it must be 
   designed for attachment to the External drive connector on the adapter, 
   i.e. having the 37-pin type D connector on the controller end. the cable 
   must have the IBM 'twist' on the floppy connector at the end of the cable.

   (Note: The 34-wire flat cable is attached to the 37-pin connector such
   that the stripe is towards the pin-1 end, but the cable is offset all
   the way to the pin-37 end. Because of the way the pins are laid out, 
   wire-34 will actually go to pin-19 and wire-1 will actually go to 
   pin-21.)

   If you're going to have this made, tell the supplier that it's going
   to the external connector, so they'll make it a little longer -- about
   6" -- than normal. This will make it a little easier to route.

3) The IBM external floppy software driver, EXDSKBIO.DRV. This has the
   IBM p/n #6280666. However, you may find that you can obtain this for
   free from your friendly IBM dealer... It comes with the IBM 3.5"
   External drive adapter kit, (That kit includes the IBM external drive.)

4) Of course you'll need the floppies. For an internal 3.5x720k drive,
   The TOSHIBA ND-353A/354A, with the internal mounting kit is suggested.

What to Do:

1) EXDSKBIO.DRV is coded for just one drive. In order to provide for
   two drives, we make some patches and end up with two files. These are
   then loaded as device drivers in the CONFIG.SYS files, as will be shown.

   Make two copies of EXDSKBIO.DRV, naming them EXT1.DRV, and EXT2.DRV.
   (Your 'original' unmodified EXDSKBIO.DRV should be put away for safe
   keeping.)

   Included in this ARC file are PATCHER.BAS, EXT1.PAT and EXT2.PAT.  Have
   BASIC (or GWBASIC), PATCHER.BAS, EXT1.DRV, EXT1.PAT, EXT2.DRV, and 
   EXT2.PAT on the same disk, and in the default drive.  Now Boot BASIC 
   and run PATCHER twice. The first time enter EXT1.PAT when asked for 
   "patch file", and EXT2.PAT the second time.  If all went well, you will 
   now have two patched drivers EXT1.DRV and EXT2.DRV.

2) After the installation that follows, the two new drives will be 
   recognized AFTER ALL of your current physical and ramdrives. Place
   the following in your CONFIG.SYS file, after any device drivers you
   may have:

   DEVICE=EXT1.DRV                        (Both MUST be loaded 
   DEVICE=EXT2.DRV                         BEFORE the DRIVER.SYS')
   DEVICE=DRIVER.SYS  /d:2 /c              (For 3.5/720kb drives)
   DEVICE=DRIVER.SYS  /d:3 /c              (For 3.5/720kb drives)

      (Note:  If you've made the new drives 5.25x360kb's then the 
      DRIVER.SYS params would be: /D:2 /T:40 /F:0 & /D:3 /T:40 /F:0.
      These additional params, T & F, are not needed for 3.5x720kb's 
      because those are the default for DRIVER.SYS.  The /c is necessary
      for those drives that need the changeline feature. Changeline
      is used for ALL drive types, EXCEPT 5.25x160/360kb.)

3) Turn off the computer and unplug it.  Remove cover.  Make a slot 
   available, preferably on the drive side of the floppy controller you 
   now have.

4) Remove the bracket from the External Adapter, (EA).  Cut out the side 
   of the bracket, the entire length of the connector slot, on the RIGHT 
   side, (top angle of bracket facing rear of computer, just as it will 
   be when installed).  Do this on an angle at each end, but don't disturb 
   the connector mounting holes.  Reconnect the bracket to the EA.

5) Thread the drive cable through the slot in the computer, stripe end
   up.  Install the EA, being careful not to pinch the cable. The fit is
   very close, but it will go.  Test by moving the cable up and down a
   bit.  Be sure you feel at least a tiny amount of play. Connect the 
   cable to the EA.

6) Install the drives.  A jumper should be set to enable DC, (Disk Change) 
   IF the drives are ANY BUT 5.25x160/360kb units.  For those units,
   Disk Change and Disk Ready, sometimes labeled DC or SR respectively, 
   MUST NOT be enabled (jumpered).  

   Disk Change is the 'changeline' feature mentioned in connection with 
   IBM's DRIVER.SYS documentation.  Disk Ready or Standard Ready or just 
   Ready, is NEVER used with an IBM PC/AT regardless of drive type!

   Set a jumper for Drive Select line 2.  (DS2 where numbers go from 1 to 4 
   and DS1 where numbers go from 0 to 3), for BOTH units.  Also, for Toshiba, 
   be sure the jumper on the internal mounting kits pc connector board is 
   set for PC/XT, and NOT for AT.  For the Toshiba 3.5x720 then, install
   jumpers on DC and DS2.

7) Connect the new floppy cable to the new drives. The connector at the
   end of the cable must go to the drive you want to be first "logical"
   drive of your new sequence. That is, if your new drives are going to
   be say D & E, then D would be the FIRST "logical" drive, and would
   take the connector at the END of the cable. (To say it another way,
   the first logical drive is the one following the 'twist' in the cable.)

   Note that the stripe end of the drive connectors goes to the right, (as
   you face the front of the computer). Same side as any other floppies
   already installed. 

8) Power for the drives comes from the computers power supply through
   the same power lead setup as powers the other internal floppy(s).
   Your computer may have additional leads for this provision, or you
   may have to have some "Y" cables made up to handle it.  Power does NOT
   come from the 34-conductor cable.  Drives have frame grounding lug.
   In most cases it is only necessary to ground the frame of one drive.
   This usually serves to ground them all.  However, should you get 
   frequent drive errors, you should ground the affected drives.

9) At your floppy controller, note the orientation of the stripe on the 
   'internal' connector/cable for your current A:/B: drives. Then 
   disconnect it from the controller. 

   Take the short cable that came with the EA.  Attach one end to the 
   floppy controller where the A:/B: cable was, with the stripe oriented as 
   per the A:/B: floppy cable.  Attach the other end to the connector at 
   the 'front' end of the EA, stripe to the 'rear'.  Connect the A:/B: 
   cable to connector at the 'rear' of the EA, stripe to 'rear'.

10) You're done.  Boot the computer.  If formerly you had drives,
    A/B as floppies and C as an HD, and D as a ramdisk, you will now
    have additionally, E and F as your new drive designators.  As the
    system boots, you should see the messages, "FIRST EXTERNAL DRIVE
    LOADED" and "SECOND EXTERNAL DRIVE LOADED".

    Test the setup first by reading something from each of your drives.
    If all seems well, then write something to each.  Lastly, try
    formatting a disk in each new drive, and run CHKDSK on them.

                            -END-