[Pc_Support] PCI-Express SATA card for $22 (NCQ, 3gb, etc)

[Bryan J. Smith]

On Sun, 2005-11-20 at 21:02 -0500, Damien McKenna wrote:
> I didn't realize NC was reliant upon software, I thought it was a 
> hardware thing?

It is and it isn't.  ;->

In SCSI, you have a hardware host (the host adapter), and you have a
hardware target (the drive).  The host can queue for all targets, and
the target can queue and service several commands from the host.

In ATA, you do _not_ have a hardware host (the card/bridge is just a bus
arbitrator -- the PC is the host), and the integrated drive electronics
(IDE) is the target.  Even if the target can queue and service several
commands from the host, the host _still_ must send/manage those
commands.  Hence why you need a driver that can do NCQ.

That's where the Advanced Host Controller Interface (AHCI) comes in.
It's a software specification that _all_ [S]ATA** controllers are
supposed to comply to, so a host (the PC) can drive up to 32 different
devices (which may be spread over various controllers).

[ **BTW, AHCI and NCQ aren't just SerialATA things, they are general ATA
standards.  AFAIK, there are no [Parallel] ATA cards/targets that
implement AHCI/NCQ, but there's nothing technical stopping such. ]

> Only worse, at least when they would say SUB 2.0 High Speed it really 
> was a 480mbit device, rather than from what you're saying where they're 
> claiming SAT-3gb support but aren't delivering.

It's all a marketing game.

SATA 3GHz and 6GHz was _supposed_ to require a twisted pair SATA cable.
That's why they call it SATA-IO, which does.  I haven't seen such a
requirement out of alleged SATA-II.  So there are SATA-IO complaint
SATA-II, and then there's marketed SATA-II.  ;->

SAS 3GHz does require twisted pair SATA cables AFAIK, but I haven't seen
what the specs/standards are.  Of course, SAS 3GHz goes up to 8m,
instead of the standard 1m for SATA.


-- 
Bryan J. Smith   b.j.smith at ieee.org   http://thebs413.blogspot.com
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