The Disk Module allows for adding DASD to a Gearbox.  The Disk Module consists of a double-wide shroud and a Disk/Diskette Adapter Card, to be plugged into the  frame in place of two empty card shrouds.  The Disk/Diskette Adapter Card contains 0.5MB of DASD Cache Memory, and supports up to two 1.6" high 3.5" drives and a 1.44MB Diskette Drive installed inside the shroud.   The DASD Module has a C60 SCSI port on the bottom.

SCSI BIOS Upgrade Ready
   The upgrade SCSI BIOS chips for the SCSI and SCSI w/cache (92F2244/92F2245) work in this board, and probably all others. If you look at the SCSI w/cache, single oscillator, the parts are the same.

NOTE:  PS/2 adapters should not be installed in the slot #9 position. This is due to limitations with setup and diagnostic code recognizing such adapters in that position.

2.88MB Support
   The D40 (possibly C40 as well) support the 2.88MB floppy. It's in the setup options...

Set ID
  Your C: MUST be set to ID6, a second HD MUST be set to ID5, as the setup lacks selectable start sequence. The SCSI adapter itself is ID7.
   Something I haven't seen- if you add an auxiliary DASD module to slots 1 and 2, the drives must use ID0 to ID4. The drives within the Auxiliary DASD module are considered as external SCSI devices. 

Hard Drive Shapes Supported
   The 7568 requires the squarish 0661/0662/0663/0664 drives to fit the 7568 specific drive rails. The mounting holes on the 1" high 0662 do NOT match. You can drill a new pair of screw holes in the rails, but keep this in mind- the on-board SCSI is 50 pin, so why not keep with the 0662/3/4 1GB-2GB range?

Some pictures stolen from Alfred Arnold's page:

Remove the Floppy Drive
   Remove the clear plastic spacers between the drive latches. Unscrew the two screws on the outside of the shroud (they screw into the FD's bottom!). Spread the two sets of latches one side at a time, pulling up on the FD. Once the FD rails are past the latch, pull it back and up.
   The floppy rails are held on with two screws per side. The funky thick black bezel will come off quite easily AFTER you unscrew the front rail screw. Trust me. Do NOT try to pry the thick bezel off, it is rather ready to fall off once the front screws are half way out.

40-pin to 34-pin Cable Hack
All hail Bob Eager!
  His  Making a diskette drive adaptor  provided me with the extremely important pinout information that inspired the following Super High Intensity Tinkering (S.H.I.T.). 
   The D40 BIOS (maybe C40 as well) supports the 2.88MB floppy (with it's dust shutter!). But the 2.88MB has a different location for it's 34 pin header and it's slightly offset, so the floppy cable HAS to be longer.

Waiting for a 40 pin to 34 pin cable, 27 Feb 01
  Martin Adams is sending me a 40-34 pin cable as we speak. His picture of it looks a bit different from what I've tried.

Back to the normal channel...
   My first attempt failed, I must see if it's the cable or the drive. I got a 1.44MB to try now... 
   Bob had a normal hack, but with the help of Jolt cola and a loose grip on reality, I came up with a higher hack (think outside the box!). The MAD Hack eliminates the two loose conductors between the headers, and has them securely fastened by the 40 pin connector itself. No tape needed to keep the cable together...

   Take needlenose pliers, pull the insulation displacing points on the 40-pin header at 3, 6, 35, 36, 37, and 39. Leave 38 and 40 at the end.

   Now use a 10" length of 34 conductor cable.  Crimp on the 34 pin header, Watch the orientation of the floppy header- on my FD, the key points down. Thankfully, pin 1 on the floppy and pin 1 on the DASD board are both to the left as you look at the opened module (with the floppy shutter pointing towards you). 
   Now measure out 8". You should have about 2" past the 40 pin header. Now bring out 3 and 6, cut the rest of the conductors flush at the 40 pin.  Now bring them around the back, over 38 and 40 and exit the connector towards the 34 pin header. Crimp. A little ticklish getting 3 and 6 onto the slots of 38 and 40, but it's sooo much neater.

SCSI Adapter Memory Location
   Selects a 32kb memory block which this adapter will use for it's BIOS ROM.  There are five memory ranges.
  <"Segment C000" >(mem c0000-c7fff), "Segment C400" (mem c4000-cbfff), "Segment C800" (mem c8000-cffff), "Segment CC00", mem cc000-d3fff), "Segment D000" (mem d0000-d7fff), "Segment D400" (mem d4000-dbfff), "Segment D800" (mem d8000-dffff), "ROM Disabled"

SCSI I/O Address
   Choose the I/O address for each adapter
     <"3540-3547"  (io 3540h-3547)>, "3548-354F"  (io 3548-354F), "3550-3557"  (io 3550h-3557), "3558-355F"  (io 3558-355F), "3560-3567"  (io 3560-3567), "3568-356F"  (io 3568-356F), "3570-3577"  (io 3570-3577), "3578-357F"  (io 3578-357F)

SCSI Arbitration Level
  Select the arbitration level that SCSI will use to transfer data.
     <"Level C" (arb 12)>, "Level D" (arb 13), "Level E" (arb 14), "Level 1"  (arb 1), "Level 3"  (arb 3), "Level 5"  (arb 5", "Level 6" (arb 6), "Level 8"  (arb 8), "Level 9" (arb 9), "Level A" (arb 10), "Level B" (arb 11)

SCSI Adapter Fairness On/Off
  This controls whether the adapter will  release control of the bus when it has been using it exclusively.
   <"On" >, "Off"

ROM Wait State Disable
   Enable/Disable ROM Wait State
     <"Enable Wait State">, "No Wait State"

SCSI Adapter Address (ID)
   Change the SCSI ID of the adapter.
     <"7">, "6", "5", "4", "3", "2", "1", "0"

Address Burst Boundary
Determines the maximum number of bytes per burst
     < "No Boundary">, "32-Byte Boundary", "64-Byte Boundary", "128-Byte Boundary"

Diskette DMA Arbitration Level
   DMA channel the diskette adapter will use to transfer data.
     <"Shared level 2 only" (ARB SharedArb 2)>

Diskette Adapter Fairness On/Off
   Controls whether the diskette adapter will release control of the bus when it has been using it exclusively.
     <"Off">, "On"

Diskette Primary/Alternate Addresses
   Primary or secondary address range of the diskette portion.
     <"Primary 03F0-03F7"  (io 3F0-3f7 int 6)>, "Alternate 0370-0377"  (io 370-377 int 6)