In almost all cases of designing a circuit board, Pin 1 is ground. It used to be that there was some sort of keying scheme to avoid putting a cable on backwards. In the case of IDE drives, Pin 20 was not used, and some cable makers put a plug in, with the idea it would match up to a missing pin connector on the drive. In other cases, the plastic housing of the connector had a plastic key.
The challenge was, nobody got all the manufacturers together, and got them to agree on a standard. (Why do we need a standard? We have a bunch of them already!) So, some manufacturers did or didn't do one or both, or neither. (It's real 'fun' to stand there with a pocketknife attempting to either remove a plug, or shave off the plastic tab from a cable so it fits either a drive or motherboard. I have the scar of five stitches in my hand to prove what 'fun' it was.)
So today, we have to 1) be sure not to reverse cables when installing, and 2) carry a very sharp knife with a small pliers to hold the connector. As an alternative to #2, carry extra cables without the plug or plastic tab.
In the continued struggle toward more speed, ATA is expected to hit the ceiling at 133 MB/sec. Some analysts feel that 133 MB/sec with ATA/133 is the limit. In either case, there's no argument there are several issues involving (parallel) ATA. Factors including:
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