Floppy

The original floppy cable required that each drive was jumpered to the right ID. But IBM come up with an idea to avoid jumpering the floppies.
If wire 10-16 are twisted before the last connector the jumpering is avoided. Each drive should be jumpered to act as Drive 2. If only one drive is used then leave the middle connector free.
The IDC could also be an edge connector on some old drives.

Controller           Drive 2   Twist   Drive 1
+--+                   +--+            +--+
|::|===================|  |============|  |  <-Pin 1
|::|===================|  |=====\/=====|  |
|::|===================|  |=====/\=====|  |
|::|===================|  |============|  |
|::|===================|  |============|  |
|::|===================|  |============|  |
|::|===================|  |============|  |
+--+                   +--+            +--+

34 PIN IDC FEMALE (to the Controller)
(to the Drive 2)
(to the Drive 1)

34 PIN IDC FEMALE to the Controller.
34 PIN IDC FEMALE to the Drive 2.
34 PIN IDC FEMALE to the Drive 1.

	Controller	Drive 1	Drive 2
Wire 1-9	1-9	1-9	1-9
Wire 10	10	16	10
Wire 11	11	15	11
Wire 12	12	14	12
Wire 13	13	13	13
Wire 14	14	12	14
Wire 15	15	11	15
Wire 16	16	10	16
Wire 17-34	17-34	17-34	17-34

Contributor:

Joakim Ögren

Source:

TheRef TechTalk