Giganews Newsgroups
Subject: Re: SCSI/SATA
Posted by:  Paul (
Date: Mon, 23 Sep 2013

Johnny wrote:
> I have a question about a hard drive.  Mine is going on five years old,
> and I'm sure it won't last much longer.
> In Device Manager, my hard drive is listed as SCSI, but I know it's an
> SATA drive.  I just wonder why it doesn't show up as an SATA?
> The hard drive is a Hitachi hdp725025gla380
> I'm going to replace it with a 500Gb 7200 RPM hard drive.
> MY hard drive is a SATA 1.5, and I notice the new drives are SATA 3,
> Will that be a problem?
> Windows 7 Home Premium 32 Bit
> Compaq
> 2.7 GH processor
> 2 GB RAM

This has to do with the fact there was SCSI driver
support built into the Windows OSes. It makes it
easier for the hardware companies and their driver
writers, to write drivers. On some driver installations,
the installer even "runs twice", depositing one level
of the driver on each of the two passes. It's quite
comical to watch.

        | SCSI storage path
      SCSI Preprocessor (first level)
        | CDB translated into actual command
      Actual driver    (second level)

The person writing the driver for your SATA drive,
"pretends" it is a SCSI drive, translates the
SCSI read or write command data block, into
something the SATA drive can use.

At one time, there was actually code in the SCSI Preprocessor
layer. There was an actual division of labor.

Now, on some of those installations, the SCSI Preprocessor
layer is nothing more than a label in Device Manager (fake layer).
And the lower driver is doing all of it. So no pretense in terms
of implementation.

Your experience might have happened, if there was some
Silicon Image separate chip for the SATA drive. If the SATA
drive was connected to the Southbridge, then the Windows 7
built-in IDE/AHCI/RAID drivers can take over, and the
word SCSI probably doesn't appear for those.

And the fun started, because there was an existing SCSI
stack, in even the old Windows OSes. And the hardware
people were even encouraged to use that route.
It wasn't an accident, but a convenient way to get the
job done. It could have meant, slightly less support
from Microsoft, to get driver writers to be successful.


SATA III would be a problem on some older VIA and SIS chipsets.
There used to be a tech note from Seagate on the matter.

Try page 11 here.

One poster claims the VIA 6421A is "fixed". And my VIA 8237S
worked OK with a SATA II drive. Otherwise, with
a SATA III drive, it only jumpers down to SATA II,
rather than SATA I. And then a SATA III drive would
not work, on one of the page 11 listed pieces of hardware.

You would need to learn more about your motherboard hardware,
to be able to predict success or not. The odds of
you arranging the right stuff to have a failure,
are pretty low. Lots of other hardware, will negotiate
down when required to do so. (I.e. Older SATA II or SATA I
motherboards, can work with SATA III drives. They're supposed
to negotiate a lower rate. And I don't know the flowchart
for that sequence, and how they decide to "gear down".)



In response to

SCSI/SATA posted by Johnny on Mon, 23 Sep 2013