On Thu, Apr 13, 2000 at 05:53:48PM +0100, Wesley Darlington mentioned:
> Speaking of udma66, what's the deal with these fancy udma cables with 80
> conductors? Since there are only 40 pins at either end, what's the deal
> with having 80 conductors. Do 40 go to one hard drive and 40 to another?
> Can one do udma66 with a 40 conductor cable? While I'm asking da questions,
> what's different between udma33 and udma66 apart from speed? Does 33->66
> imply some difference in the ata command set?
There is a difference in the command set - stuff like tag queueing can be
implemented, to make it more like SCSI.
The extra wires are just grounding wires. As the bus runs at a higher
frequency, there is more crosstalk/interferenece between data cables, so
wrapping an extra ground wire around each one reduces that a lot (like the
way twisted pair works).
You can connect a UDMA66 drive to a UDMA66 connector, with a standard 40
pin cable, but I reckon that the higher error ratio will force it back to
UDMA33 at most.
Hmm. I also remember that there are black and blue terminators now, on
the cable (you have to put a single drive at the end of said cable now).
Probably also means that you need terminators on the cable, before it'll
do UDMA66 too.
"The fool must be beaten with a stick, for an intelligent person
the merest hint is sufficient" -- Zen Master Greg
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