15 May
2014
15 May
'14
11:47 a.m.
I don't recall the specifics as to why they used
80 conductor wired
for a 40 pin connection; I believe it had something to do with
reducing crosstalk & interference at the higher speeds of the (at
that time) newer hard drives.
The version I saw is that the other half of the wires are grounded at
the CPU end and exist as shielding for the other lines - basically, as
you say, to reduce crosstalk and other intra-line interference.
While I'm a good deal less sure of this, I also have the impression
that there is some other difference - an otherwise unused pin grounded
in the connector? - which (a) serves to notify the host electronics
that it's got an 80-wire cable and (b) means that the host connector is
operationally different from the drive connectors (which isn't the case
for 40-wire cabling).
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