From:	Kevin Quick <kquick@iphase.com>
Date:	Thu, 24 Sep 1998 14:14:12 -0500 (CDT)
To:	linux-kernel@vger.rutgers.edu
Subject: UDI VCR analogy

There's a great deal of documentation on the UDI web site
(http://www.sco.com/UDI) which describes what UDI is... all the way
from general white papers to the explicit specification.  I realize
most of you don't necessarily have time to dig into this information
but would like to understand what UDI is all about.  Therefore I'm
offering this crude analogy.  Please understand that this is just an
analogy and don't take it too far, but here goes:

UDI is analogous to the VHS specification for video tape recorders.

VHS completely specifies how the tape and the tape player interact.
This includes physical components (size, location of wheels, width of
tape, where to place the playback and record heads, etc), the
mechanical components (how fast to move the tape across the heads),
and the electrical components (where on the tape the video is
recorded, where the sound is recorded, what the formats are).

If the VHS specification neglected to specify any of these components, 
then tapes wouldn't be portable.  Because of the VHS standard, you
know that any VCR marked as VHS supports tapes will play any VHS tape
that you buy or rent.

Now think of the VCR as the operating system and the tape as the
device driver.  UDI is a specification which completely describes the
interface between the driver and the operating system... no
OS-specific code is found in the driver.

VHS does not tell you what to put on your tape or dictate the quality
of the product.  UDI does not require you to have a special type of
hardware interface and similarly does not dictate the quality of the
driver written.

VHS does not tell you what features your VCR may or may not have or
how it's packaged or how much it costs.  UDI does not impose similar
limitations on the Operating System beyond the fact that it must
conform to the UDI specification just as VCRs conform to VHS
specifications.

How does I2O fit into this?  Keeping the analogy rough, let's say that 
I2O is a new audio encoding format designed to provide surround sound
separate channels and superlative quality and signal-to-noise
rations.  However, this audio encoding is wisely backward compatible.
Now you can get an "I2O audio" recorded VHS tape and it'll work in a
standard VHS VCR but it sounds fantastic in an "I2O VCR".

I'll stop there... I think you get the idea.  For a better
understanding, the documentation available from the web site is really 
the best place to go, or ask me more specific questions.

-- 
________________________________________________________________________
Kevin Quick        Interphase Corporation Engineering      Dallas, Texas
kquick@iphase.com        http://www.iphase.com              214.654.5173

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