14 Mar
2005
14 Mar
'05
5:14 p.m.
Richard wrote:
4) All RW media (DVD-RW DVD+RW CD-RW) have poor
archival life.
Think about it: with RW, instead of burning a pit in the data
layer, you are fooling around with glossy or matte finish
depending on how quickly a melted liquid re-freezes. Official
tests, and my own tests, show poor life. A little sunlight-UV
can erase it.
Eric wrote:
It was my understanding (perhaps wrong?) that RW media
uses a phase
change to store the data, and that it takes significantly more energy
to induce the phase change than to induce a chemical change in dye
for write-once media. That's why it can't be written as quickly.
If it really works that way, one would reasonably expect RW media to
have *better* longevity than write-once media.
So is my premise wrong? Does rewritable media not use a phase change?
Or is the activation energy comparable or lower than that for write-once
media?
I don't know about activation energy. Sorry. But the resultant RW
disk is less reliable, and has shorter archival life.
Richard:
My least favorite factory is CMC Magnetics
Eric:
They seem to make about the worst CD media, so it's
unsurprising
that they make poor DVD media.
Richard:
I think Pioneer and Verbatim buy their media from
the good Japanese companies, Mitsubishi, Taiyo Yuden, and Mitsumi.
Eric:
By "Mistumi" you must have meant
"Mitsui"? For CD media, Taiyo Yuden
and Mitsui are definitely the best.
Richard:
Yes, I meant Mitsui. It was a typo. Mitsumi is I think a maker
of floppy disk drives in Japan, and not media. Mitsui and Taiyo Yuden
make good media, and sell organic dyes and other chemicals to many
of the lesser media making companies.
Richard:
TDK seems to be only advertised brand that makes their
own
Eric:
I used to buy TDK CD-R media at Costco because it was
made by
Taiyo-Yuden. Then they switched to CMC Magnetics, and after
using one spindle of that (with >50% reject rate), I refuse to
ever buy media from them again.
I'm surprised that TDK would make their own DVD media when they don't
make their own CD-R media. More likely they're contracting out
manufacture and getting the vendor to mark the metadata as TDK.
Eric
Richard:
I'm sorry to hear that. I know their media code says TDK,
but you are correct, maybe they didn't make it. But it tested
well.
========== ADDITION TO RICHARD's PREVIOUS POST =====
In my original message, I forgot to add: ...
7) If you really care about it's archival life, hedge your bets
by burning two copies, on DIFFERENT media. Select two good
media types made by different companies. Each may have, just
a guess, a 10% chance of self-destructing within 20 years.
This would be because of a design or implimentation mistake.
For example perhaps the sandwich adheasive includes a chemical
that eventually reacts badly with the data, or some impurity
in manufacturing at that time. If the two media are very
different, their probabilty of failure approaches statistical
indpendence; and if independent then the chance that both are
unreadable would approach 0.1 * 0.1 or only a 1% chance.
Richard Bristol bristol22 [at] softhome [dot] net