VWWall wrote:

The early hard drives used FM or MFM data, and were driven from track to
track by
a stepper motor. The cable twist still survives in floppy cables,
although few computers now have more than one floppy drive. Cable
select on modern ATA drives is done by a ground on pin 34, which tells
the controller which is the master. Pin 34 on the slave, (middle,
gray), is not grounded as it is on the end, (black) connector. The cable
supplies the ground at the MB, (blue) connector, and the system will
complain if a 40 wire cable is used for a drive that needs an 80 wire
cable, since no ground will be seen by the MB controller.

Oops! Change: pin34 to pin 28, (CSEL). Pin 34, (CBLID), *is* used to
determine if an 80 wire cable is needed by grounding pin 34 at the MB.

Virg Wall, in a hurry to get to the turkey!