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LOSTCIRCUITS	SHORTCUTS: Top Page Pitfalls in Parallelism Seven Deadly Limitations (I) Seven Deadly Limitations (II) Tagged Comand Queuing Transitional Solutions SATA Clocking, LVDS and Cabling Staggered Pins For HotSwap Cyclic Redundancy Check Error Detection Seagate Barracuda SATA V Test Setup and HDTach WinBench 98 Business WinBench98 HE Conclusion
Seagate Barracuda SATA V Serial ATA and the 7 Deadly Sins Of Parallel ATA
(Review by MS, September 15, 2002)

4. Pandora's Box of Connector Legacy

There are several caveats associated with the move to 80 wire cabling. First, the required legacy support and backward compatibility also requires the carry-over of the existing connector form factor. This, in turn, means that the physical width of the connector has not changed and now needs to accommodate 80 wires instead of 40.

As a consequence, the individual wires used in the ribbons need to use a smaller caliber. Smaller caliber means higher resistance and, by extension, lower signal propagation speed. This opens up an entire new Pandora's Box of problems in that the signal potentially ramps up faster than it is propagated. Again, for easier understanding, we resort to an analogy and the most intuitive example is a sonic boom. In other words, the signal voltage ramps up faster than it can be moved away from the source of origin. This leads to differential voltages across the data lines, a situation that can further be exacerbated if the feedback circuitry shows too little voltage at the receiver end and the controller keeps pumping up the lines. The result is inflated signal amplitudes that will reflect at the end of the cable and travel back in opposite direction to collide with the next set of data.

UDMA (ATA PI-4) vs. UATA (ATA PI-5) cables. It is easy to see where the additional wires necessitate a finer pitch with all electrical trade-offs described on this page.

As we outlined in an earlier article, those design induced problems, that is, the trade-off between elimination of cross talk and avoidance of signal ringing are the reason for the strict designation of the individual connectors on any UATA ribbon cable as "board", "master" and "slave" that cannot be reversed without disturbing the balance and potentially damage the drive. Likewise, folding of the cables, rounded and spliced cables can be fashionable but one thing they are definitely not is electrically clean. This is why rounded cables will increase the failure rate of HDDs regardless of their esthetic value.

5. Termination

Another issue playing into the signal properties of the parallel path is the termination of signals. Briefly, to avoid signal reflection at the end of a cable, the individual lines can be terminated, that is, tied to ground via a resistor that will eliminate any voltage swings above a certain level. Usually, the drive itself provides the termination and as mentioned in our earlier article, this termination is the reason why single drives need to sit on the end of the cable even if it involves longer distances. Of course, there is always the possibility to simply cut off the tail end of the cable, which solves most of the electrical problems but also has the negative side effect of eliminating the use of a master-slave configuration.

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