Difference between IDE and SCSI ??

[Lamar Owen]

On Tuesday 05 February 2008, William Case wrote:
> My question is not about the history of the various chips etc., but is
> about why do I get three different designations on my computer and how
> do I disentangle the information being given me so that I know what is
> what?

This is somewhat of a different question, then.

To tackle things in order:

1.) The nVidia MCP is not a SCSI controller.  Yes, I know the linux kernel's 
libata driver stack treats it like a SCSI controller, but it is not one, it's 
just emulated.  The same is true of USB drives; they are treated like SCSI 
drives.  Alan Cox can chime in with the reasons why this was done.

2.) The seeming discrepancies you are seeing are results of the 
IDE-SCSI 'merge' in the libata software stack that makes IDE/ATA devices look 
like SCSI devices to the kernel.  So, you get entries 
in /sys/bus/scsi/devices/ that seem to conflict with /dev/disk/by-id; in 
fact, the 'ata' you see is telling you that the drives are IDE/ATA drives, 
not SCSI drives.  The kernel, thanks to the libata driver stack, displays 
them in the SCSI tables since, for all intents and purposes that the kernel 
cares about, libata exposes the drives as emulated SCSI drives, even they 
they are not SCSI, but IDE/ATA.

Yes, I know it is a tad confusing.  You can find more information on the 
libata pages at http://linux-ata.org/ (even though that page is mostly about 
SATA, the information applies to the parallel 40-pin PATA IDE drives too, at 
least in Fedora 8).
-- 
Lamar Owen
www.pari.edu