the cables i have are twisted pair ribbon cabling. it's the same type as the twisted pair laminated SCSI cables without the lamination. the twisted pair is great for exactly what has been said, to reduce crosstalk due to induction caused by changes to the EM field. of course since the pairs are bundled up together, this produces a flaw which is the difference between CAT5 and CAT6 wiring standards, the latter isolating each pair in a jacket. this bundling cancels some of the positive effects of having twisted pair cabling, but it's better than cutting up a flat cable and bundling it. especially since those 80wire cables are a bitch to work with.
personally, both types of cabling are annoying to work with. flat or round, having 80 wires is just takes a lot of space...
<------ gonna be an early adopter of serial ATA.
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if you want optimal performance, get one of those rounded twisted pair cables, remove the jacketing, isolate each pair with a jacket, and shield the damn thing. of course this would produce a hell of a mess of cable-age. =P