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Date:	Sun, 15 Aug 2004 13:14:18 PDT7
From:	Peter Skye <pskye@peterskye.com >
Reply-To:	scoug-help@scoug.com
To:	scoug-help@scoug.com
Subject:	SCOUG-Help: CD Longevity

Content Type: text/plain

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J. R. Fox wrote:
>
> I've been putting a lot of reliance into the
> medium of CDs, for storage, backup, etc. It is
> quite possible this reliance has been misplaced.

Foxey,

You are correct that CDs and DVDs may not have a long life expectancy.

-- 1. The materials design of CDs and DVDs has a known chemical
breakdown lifetime. All materials do. Did you know that concrete has a
typical lifespan of only 100 years? (Caveat: there are a myriad of
different formulations for concrete to make it stiff, spongey,
lightweight, waterproof etc and the different formulations have
different life expectancies.)

-- 2. Manufacturing quality control. There isn't a single CD or DVD
that's ever been manufactured which exactly met its specifications. The
tolerance drift is maddening but it's the best they can do. Any given
platter might be far enough out of tolerance that the life expectancy is
noticeably lower than desired. I'm not just talking about the final
manufacturing stage; there are a number of suppliers who create the
materials used for the manufacturer, and then there's the tolerance of
the equipment used for the final manufacture. I have a lot of
experience with a prior technology -- magnetic tape -- and you would be
aaaaamazed that we ever were able to record anything at all. As for CDs
and DVDs, an article of mine published years ago is probably still
apropo: Do you really think that the center hole is truly in the center
of the disc? 'Cause it ain't. And that can make playback a bit
problematic if your current player is also on the outer limits of
manufacturing quality control.

-- 3. Storage of finished materials. Temperature fluctuations cause
material stress. Humidity causes the label adhesive to creep. Changes
in reflectivity over time.

-- 4. An article a few weeks ago in either the Los Angeles Times or The
Daily News reported that CDs are actually eaten by some weird
andromeda-strain microbe even under ideal storage conditions. If you've
had any visitors from Andromeda you need to start worrying about your
CDs _now_.

Everything should be backed up, and that includes your CD and DVD
collection. I recommend backup to hard drive because it's easy to
administer, easy to copy, easy to restore (just store the ISO image).
The cost of hard drive storage is somewhere around 50 cents for a
gigabyte (I bought a 250 GB Western Digital IDE drive on sale at Fry's
last week for $119, no rebate required). That's about 35 cents to make
a copy of a full CD or much less if the CD isn't full.

- Peter

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