@Glaucus:
IIRC you have to use a special cable for UDMA modes 4 and 5 (it's the one with lots of small wires but the same amount of connections as the "normal" cables). This is the case even with PCs, I think it's got to do with the thicker wires causing interference on each other at high transfer speeds, the thinner wires don't have that problem.
@Downix:
