Newsgroup: it.comp.macintosh
Titolo: [iMac] CD che scottano!

E' molto dannoso per i CD (sia audio che mp3) il calore?
Se ascolto CD sul mio iMac DV 400, (cioè tutti i giorni, mattino
pomeriggio e qualche volta anche sera), quando li tiro fuori sono
caldissimi! (tralaltro: e' normale, vero?)
Io per precauzione cambio ogni 45/50 minuti. 
Non e' che se me lo dimentico su...
dopo un po' si scioglie??? ;-)
Ciao,
ortospace
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 dopo un po' si scioglie??? ;-)
I Cd non si rovinano, puoi andare sicuro!!

 I Cd non si rovinano, puoi andare sicuro!!
Non ne sarei cosi' sicuro.... leggi cio' che si documenta in questo
articolo:
+---------------------------------+
Do Compact Discs Degrade?
by Bob Starrett
The answer to this question is easy and apparent: of course compact
discs degrade. As with every other material, eventually time,
temperature variations and the elements will take their toll, on the
disc as a whole, as well as each element that comprises that disc. The
real question is, how does disc degradation affect readability?
According to the Optical Storage Technology Association (OSTA), CD-R
discs have a long lifespan:
"Lifetime estimation of any storage medium is a very complex and
statistics-based process. Improper testing or measurement procedures can
seriously impact and compromise lifetime estimates. ANSI Committee IT-9
is currently developing comprehensive guidelines for CD-ROM and CD-R
life estimation. The CD-R media manufacturers have performed extensive
media longevity studies using these industry-defined tests and
mathematical modeling techniques, with results claiming longevity from
70 years to over 200 years. The primary caveat is how you handle and
store the media. With proper handling and storage, your CD-Rs will
outlive you."
It is one thing to say that discs will last that long. But while we grow
old waiting to find out, we need to take some precautions and not rely
stiffly on numbers such as these.
How long can you store a disc before you need to possibly reburn it to
preserve your data? And is a CD really the best place to store important
data for a long period of time? A comprehensive study of this topic is
best left to someone or some company that has the deep pockets to
perform it. The resources necessary to burn, test, age and retest media
of different dyes, reflective layers and coatings are enormous.
In the meantime, the best we can do is use existing surveys and
anecdotal evidence as a guide. While somewhat old, two studies are also
available that provide a little insight into how the media manufacturers
look at the longevity issue.The studies are rather technical, but if you
want to look at them you can find them here:
TDK - 
http://www.cd-info.com/CDIC/Technology/CD-R/Media/TDK.html
Kodak - 
http://www.cd-info.com/CDIC/Technology/CD-R/Media/Kodak.html
US News and World Report also has an interesting article with a useful
chart comparing the lifetimes of several types of storage media. It
draws the startling conclusion that unless you buy certain high-quality
brands, your CD-R discs may last as little as two years! But note that
the National Media Lab took issue with the manner in which its data was
used to produce the chart and does not agree with the conclusions drawn.
http://www.usnews.com/usnews/issue/980216/16digi.htm
It sure would be nice to conduct our own study, but let's do the best we
can with what we have on hand. Let's look at some really old discs and
see if they are readable. In my personal collection, I found three CD-R
discs that were at least 10 years old. These discs have not gone through
any aging process or artificial stimulus. They have had a nice home in a
jewel case, have made several trips to California and back, been
joggled, of course, but otherwise they should be in good shape. They are
clean discs without scratches, the kind that go into a jewel case right
after recording and stay there.
Of the three, one was unreadable in four different models of Plextor
drives, while it worked fine in a Kenwood 72X TrueX CD-ROM drive. But
the fact that the Plextors could not read it and the Kenwood could,
caused me to make a copy of it off the Kenwood, because this ten-year
old disc contains data that I may need in the future. I feel safer now
with the original and a backup that the Plextor drives are happy to deal
with.
When will I check it again? Probably in a couple of years. Does this
mean that you have to check all of you discs every so often to make sure
they are still readable? Well, not everything, but do check your most
valuable discs at least every year or two. Hopefully, you don't have so
many that this becomes an undue burden. Just try to save the checking
and re-recording for truly valuable discs of irreplaceable material,
rather than copies of popular audio CDs, for example.
The other two discs were both readable in a professional CD tester and
the Plextor drives, as well as the Kenwood drive. One had an error rate
in the CD tester comparable to a freshly recorded CD-R disc, and the
other had error rates higher than I would like, but still well within
the maximum error rate considered safe for CD-ROM discs.
These discs were not tested for errors when they were made, so we do not
know how the current error rates compare to the original and therefore
cannot really judge degradation. But we do know that out of three
ten-year-old recorded discs, one was on the edge, another was middling,
and a third was just fine after all that time. Obviously too small a
sample to draw any conclusions from, but the best we can do with what we
have. One additional thing to note is that CD-R media has improved in
the interim, at least discs from quality vendors have. There are also a
lot of no-name brands now that may be worse than our 10-year-old discs.
If your job is to manage a large collection of stored data on CD-R for a
company, then you have a rather large task ahead of you setting up
protocols and procedures for archival disc testing and re-recording. But
for most of us, the time spent checking key discs will be minimal.
So the controversy over the actual life expectancy of CD-R discs
continues and our quick anecdotal testing does not solve the mystery.
Just be careful with crucial data, use good quality media, and store and
treat it correctly. Chances are that you have at least 10 years before
you need to start worrying.
+---------------------------------+
Ciao, alla prossima
p.s.: ho impostato il followup al ng appropriato...
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