Difference between IDE and SCSI ??

[William Case]

Hi;

Can someone briefly explain to me the difference between an IDE (ATA)
and a SCSI device.  After having done due diligence with google searches
etc., I am still in a quandary. Nothing I read seems to be consistent.
Every time I think I have it figured out, I read a reference that calls
for or lists IDE devices that I think should be a SCSI reference and
vice versa.  Even going to the various standards sites doesn't clarify
it for me.  In fact it makes it more confusing.

Therefore, can someone explain, in plain language, how I should use the
terms IDE or PATA, and SCSI correctly with regards to a current
computer?  What specific attribute of a device or bus does each term
apply to?  

Given below are some questions that spring to mind.  They may be
mis-formed questions and therefore need not be answered, but they may
demonstrate where my confusion and misunderstanding are coming into
play.

e.g.
Does IDE refer to the physical device? 
Or, specifically just to the bus used? 
Or, to the driver for the device?
Or, the type of interface (plug)?

Does SCSI refer to a set of protocols used when designing the device?
Or, to a specific driver design?

Can you have an IDE device without SCSI?
Or, can you have a SCSI device without it being IDE?

Below, I have listed a few of the sites I have visited with the
definitions given to show I have found the history and some attempts at
an explanation.  I long ago learnt that any manual's reference to IDE or
SCSI usually simply meant some reference to my hard drive.  I am aware
it could also mean my CD or a DVD, but usually it is a reference to a
HD.

http://en.wikipedia.org/wiki/IDE
http://en.wikipedia.org/wiki/Integrated_Drive_Electronics
http://en.wikipedia.org/wiki/SCSI


Integrated Drive Electronics, a computer hardware bus used primarily for
hard drives and optical drives (e.g. CD, DVD)

Advanced Technology Attachment (ATA) is a standard interface for
connecting storage devices such as hard disks and CD-ROM drives inside
personal computers.

The standard is maintained by X3/INCITS committee T13. Many synonyms and
near-synonyms for ATA exist, including abbreviations such as IDE and
ATAPI. Also, with the market introduction of Serial ATA in 2003, the
original ATA was retroactively renamed Parallel ATA (PATA).


SCSI (Small Computer System Interface) is a set of standards for
physically connecting and transferring data between computers and
peripheral devices. The SCSI standards define commands, protocols, and
electrical and optical interfaces. SCSI is most commonly used for hard
disks and tape drives, but it can connect a wide range of other devices,
including scanners and CD drives. The SCSI standard defines command sets
for specific peripheral device types; the presence of "unknown" as one
of these types means that in theory it can be used as an interface to
almost any device, but the standard is highly pragmatic and addressed
toward commercial requirements.
-- 
Regards Bill