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Computer Hardware : Floppy Drives
If you have a floppy drive cable with twisted wires between the two end connectors, then the end connector is automatically drive A and the other is drive B, and if there are jumpers for each drive they must be set to DS0. If you have a straight-through cable then make the selection of each drive using the jumpers DS0 or DS1 for drive A or drive B respectively.
Typically drive selections are configured as either DS0, DS1 or alternately as DS1, DS2 to indicate Drive A: or Drive B: .
A cable is used to daisy-chain the drives. One end of the cable plugs into the floppy drive controller plug on the motherboard or an external I/O floppy drive controller card the other end of the cable has 2 connectors spaced several inches apart. The connector at the very end of the cable is drive A and the connector further inside the cable is drive B.
A cable can be a straight-through cable that looks flat from beginning to end, or one that has a "twist" in between the two end connectors. The "twist" type cables have the wires 10 through 16 twisted. This forces you to set both of the drives to the same DS setting. Both drives would be identically set as either DS0 or DS1. The twist in the cable would force the end drive to be A and the inside drive to be B.
XT style computers do not use Pin 34, but newer AT style computers use this pin to detect a diskette change on the drive. This can be a problem for some drives that instead of using the pin for "disk change" detection, they use it for Standard Ready SR signaling and can cause the drive to re-read the contents of the disk each time it is accessed.
The bottom line is that AT style computers do use pin 34 and it must be provided on the cable.
Floppy Drives can also use terminating resistors. Most of the time these are pre-installed. Typically only the end drive should have them installed.