I have two HDs attached to the same ATA ribbon cable and they work
fine. If I reverse the cable (master end to the CPU board), BIOS
doesn't recognize both drives. But some other cables do not have
this problem. What's the difference?

John Smith wrote:
> I have two HDs attached to the same ATA ribbon cable and they work
> fine. If I reverse the cable (master end to the CPU board), BIOS
> doesn't recognize both drives. But some other cables do not have
> this problem. What's the difference?

Pin 28 is not continuous through the length of the cable.

http://www.pcguide.com/ref/hdd/if/ide/conf_CS.htm

Paul

"John Smith" <(E-Mail Removed)> wrote in message
news:%(E-Mail Removed)...
>I have two HDs attached to the same ATA ribbon cable and they work
> fine. If I reverse the cable (master end to the CPU board), BIOS
> doesn't recognize both drives. But some other cables do not have
> this problem. What's the difference?

Pin 28 (and the associated conductor) is grounded by the controller. The
master drive connector connects pin 28 to the associated conductor (and is
thus grounded). The slave connector leaves pin 28 open circuit. Thus the 2
drives know which is the master by which has the grounded pin 28.

Some cable manufacturers have used a master connector which directly grounds
pin 28 within the connector itself. Thus the former type is actually
reversible, but the latter type is not.