Difference between IDE and SCSI ??

[Rick Stevens]

On Tue, 2008-02-05 at 13:54 -0500, William Case wrote:
> Hi Les and thanks;
> 
> Your yes and no type answers helps a lot.
> 
> On Tue, 2008-02-05 at 11:07 -0600, Les Mikesell wrote:
> > William Case wrote:
> > > Hi all and thanks;
> > > 
> > > I find the answers and information you have given me very helpful, but
> > > they don't quite get to the basis of the problem.  So let me try again.
> > 
> > If you want the really easy version, count the pins in the cable.  If 
> > you have a wide 40-pin connector, possibly with an 80-wire cable, you 
> > have Parallel ATE (also known as IDE).  Scsi would have 50 or 68 pins on 
> > a connector or 80 on hot-swap SCA connectors that include power.
> > 
> According to my manual I have an IDE connector (40-1 pin PRI_IDE; 40-1
> pin SEC_IDE).
> 
> > >> I have two Maxtor 40 Gb drives and AMD 64 X2 CPU on an ASUS M2NPV-VM
> > >> motherboard.  I am using F8 as my operating system.
> > 
> > The disk size is another hint. Scsi drives would be 36 Gb, IDE's 40.
> > 
> > >> How come? :
> > > 
> > >> My Hardware browser, under 'IDE Controllers' lists, nVidia Corporation
> > >> MCP51 IDE; 
> > 
> > That is your controller.
> > 
> > >> while /sys/bus/scsi/devices/ lists my two drives as SCSI
> > >> devices.  
> > > 
> > > When I look on the bottom of an old drive (from a 4-5 year old machine
> > > -- not one of the Maxtors mentioned above, but a Maxtor nonetheless),
> > > there are several chips.  One of those chips, I assume,  contains the
> > > SCSI programm, protocol, commands, that interface with the SCSI bus or
> > > SCSI bus controller. Or, is one of the chips hardwired to call on a
> > > special driver for the harddisk?
> > 
> > The current kernel calls everything scsi.  It isn't.
> 
> Oh!
> 
> > 
> > >> If I look in /dev/disk/by-id they are listed as
> > >> "ata-Maxtor-5T040 ..." and "ata-Maxtor-6E040...".
> > > 
> > > To what does the ata in ata-Maxtor ... refer.  The hard disk chips or
> > > the the MCP51.
> > 
> > The interface type.
> 
> I guess.  Still trying to figure out the interface type exactly.
> > 
> > > 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?
> > 
> > You have two hardware designations because you have a controller and 
> > disks.  The third is a lie.
> > 
> So then my disks are SCSI (or something else) and my controller is IDE
> (PATA)?

If the drives have 40-pin cables and are plugged into your PRI-IDE or
SEC-IDE mobo connectors, they're PATA or IDE (which are essentially the
same thing).  No, you can't plug PATA/IDE drives into a SCSI controller
and you can't plug SCSI drives into PATA/IDE controllers.

The kernel treats all block-replaceable storage (hard drives, ZIP
drives, FLASH drives--basically everything except floppies and CD/DVD
drives) as though they're SCSI (regardless of their physical
connections).

Old kernels separated PATA/IDE drives from SCSI with the "hd" in
/dev/hd* names meaning "hard disk" (PATA/IDE) and "sd" meaning "scsi
disk".  With new kernels, you won't see "/dev/hd*" names any longer, so
it may be easier for you to think of the "sd" in /dev/sdXY device names
as "storage device" from here on in.

> > > I have and I can look up the operation and function of the different
> > > designations once untangled, but in all my reading descriptions seem
> > > full of contradictions and open ended statements, each on its own making
> > > sense, but completely confusing when I try to apply them to my own
> > > existing machine.
> > 
> > So far you have not described any actual scsi hardware.
> > 
> 
> Does your comment mean that there appears to be no truly scsi hardware,
> or, does it mean I have failed to find and send to the mailing list some
> vital piece of information that I should have sent.  If it is the
> second, tell me what I should be looking for and where to find it,
> please ?
> 
> 
> -- 
> Regards Bill
> 
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- Rick Stevens, Principal Engineer             rstevens at internap.com -
- CDN Systems, Internap, Inc.                http://www.internap.com -
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-  Time: Nature's way of keeping everything from happening at once.  -
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