3.5-Inch Disk Subsystems

A horizontal ribbon.

Here is a front and back picture of my 3.5-inch DSHD disk pair. I built this subsystem recently from two Samsung SFD-321B drives I bought from eBay. I mounted the 3.5-inch drives in 3-1/2 x 5 x 8 inch Bud box.

3DSHD-F

3DSHD-B

I was trying to find a 2 x 4 x 8 inch minibox to house this disk subsystem, much as I did with the 5.25-inch drives. But that failed and I used 5.25-inch mounting adapters and mounted them in a shorter version of the same box as the 5.25-inch drives.

I bought these particular 3.5-inch drives because they would spin at 300 or 360 RPM. They might make a cost effective replacement for the much older 8-inch drives that were used on a lot of the old systems. I had to modify one drive to select as drive 0 from the drive 1 default. This was a simple removal and addition of a solder bridge between pads.

DC-37 to FC-34 Wiring

Here is the wiring diagram for all the cables shown below. This is my "standard" 5.25-/3.5-inch disk cable system. I can use IDC DC-37 connectors on flat ribbon cable to provide the interconnects between host computers and my "standard" disk drive pairs. Power for the drives is provided by the host computer.

        DC-37           FC-34		
        Pins            Pins

         1 ------------- 2
            20 --------- 1
         2 ------------- 4
            21 --------- 3
         3 ------------- 6
            22 --------- 5
         4 ------------- 8
            23 --------- 7
         5 ------------ 10   
            24 --------- 9
         6 ------------ 12
            25 -------- 11
         7 ------------ 14
            26 -------- 13
         8 ------------ 16
            27 -------- 15
         9 ------------ 18
            28 -------- 17
        10 ------------ 20
            29 -------- 19
        11 ------------ 22
            30 -------- 21
        12 ------------ 24
            31 -------- 23
        13 ------------ 26
            32 -------- 25
        14 ------------ 28
            33 -------- 27
        15 ------------ 30
            34 -------- 29
        16 ------------ 32
            35 -------- 31 and 33
        17 ------------ 34
            36 -------- +5V for drive 1 (red)
        18 ------------ +5V for drive 2 (red)
            37 -------- +12V for drive 1 (yellow)
        19 ------------ +12V for drive 2 (yellow)

        Odd pins 20 through 35 of the DC-37 are connected 
        together and connected to the metal shell for ground.
        

Here is a top and bottom picture of the non-twist 3.5-inch cable for the disk drive end. The top 4 pins on the DC-37 ( 18, 19, 36, and 37) are used to provide +5 and +12 VDC to the drives from the host computer. The rest of the pins provide pins 2 to 34 (bottom to top) interconnecting the FDC and the disk drive. With a non-twist cable, the disk drives need to be addressed as DS0 and DS1.

DSCN5000

DSCN5001

Here is a top and bottom picture of the 3.5-inch cable for the floppy disk controller end. The top 4 pins on the DC-37 ( 18, 19, 36, and 37) are used to provide +5 and +12 VDC to the drives from the host computer. The rest of the pins provide pins 2 to 34 (top to bottom) interconnecting the FDC and the disk drive.

DSCN0838

DSCN0839

A horizontal ribbon.

Last Modified: 19 July 2015