Difference between IDE and SCSI ??

Les Mikesell lesmikesell at gmail.com
Tue Feb 5 17:07:51 UTC 2008

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.

>> 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.

>> 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.

> 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.

> 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.

   Les Mikesell
     lesmikesell at gmail.com

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