[Gllug] re: SCSI vs SATA

[John Hearns]

On Wed, 2004-06-09 at 11:00, Richard Jones wrote:
> On Wed, Jun 09, 2004 at 10:47:47AM +0100, t.clarke wrote:
> > One thing that always puzzles me is why SCSI isn't inherently at least 8/16
> > times faster than SATA, bearing in mind that the data is transferred on SCSI
> > over more wires in parallel than SATA (as I understand it !).
> > 
> > Can anyone explain/point to an explanation ?
> 
> In very very hand-waving terms, if you have lots of wires, you need to
> make sure the signals arrive simultaneously at the other end of the
> cable.  If they might not arrive at the same time, then you need long
> setup and hold times at the receiving end, and that slows you down.
> 
> Of course the real benefit is cost: to run parallel cables at any
> speed you actually need a separate return path for each wire => huge
> inflexible expensive cables.  Serial can get away with 2 (?) wires at
> a much much lower cost.
And lets not mention running SCSI over serial links.
That's just what fibre channel does (the links can be copper or
optical). 
(As an aside, the physical layer used by fibre channel was adopted by
gigabit ethernet)

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