Susan, Jennifer,
The central problem with CDs and DVDs is the massive array of manufacturing
techniques and different material compositions of different disks. The
variety makes it very difficult to pin down any real "lifespan", although
there are averages available. Although the technology is generally the
same, the combination of physical factors makes for a wide variety of disks
with very different lifespan characteristics. The following article was the
first I came across that lays it out pretty well, and provides some dos and
don'ts for disks.
http://www.audioholics.com/techtips/specsformats/CDDVDlongevity.php
New magnetic media is just as stable as new CD/DVD technology, according to
the experts. The problem with magnetic media, such as VHS tapes and floppy
disks, is that they are more susceptible to degradation over time in the
general sense. The media is essentially a fine layer of iron atoms(some
kind of ferrite molecule) bound to a piece of mylar. Iron rusts, is very
sensitive to stray magnetic fields, and is pysically very fragile. If left
alone and stored properly, such media can still last many years before
severe data loss occurs. It is also a little more difficult to copy, and
copying and use is more likely to introduce data errors.
CD technology is based on a dye substrate and a reflective surface, which
allows the laser in the drive to adjust the chemical composition of the dye
in very tiny areas of the disk(pits). Incidentally, that is why you can see
the area of a disk that has been written to, becuase the dye has changed
from is manufactured neutral state to a randomly altered state(a long
series of 1s and 0s). The stability of any given disk(CD or otherwise)
depends on the dye, the reflective surface, the physical makeup of the
plastic disk, and the care/use it receives. No certain brand or type of
disk seems to be clearly superior, although the cheaper you go, the more
likely your disks will fail. There are many citations on cheap disks that
have ceased to function after as little as one year. Quality name brand
disks seem to be better made, and disks with a gold alloy reflective
surface are apparently a little better as well.
The National Institute of standards and technology recently released a
preliminary study on the subject, which is found here:
http://www.itl.nist.gov/div895/gipwg/StabilityStudy.pdf
The central issue is that the industry's claims of 50-100 years of life
should be taken with a giant grain of salt. All of our policies should
include an understaning that no "permanent" storage media exists for
digital data, and that there is a need for periodic copying and checking of
the data to insure its continuance. I am personally looking at instituting
a 5 year play cycle, with a 10 year replacement cycle. In other words, all
disks will be checked for playability at least every 5 years, with data
disks being opened and files run. Any faults or errors to be corrected and
new disks made. All disks will be replaced every ten years, whether or not
they are showing any signs of degradation. I will have my policy state that
all disks and previous copies will be kept, and marked as a certain
generation of copy. Eventually, (I have not decided when) the older disks
would be destroyed.
One of my concerns is that CD technology is already so common in our
everyday lives, that we might be tempted to look at the disks with less
care than we otherwise might as museum professionals, simply because we are
so comfortable with them. Despite the apparent robustness of our music CDs,
which we throw around, handle carelessly, sit face-side down, use as
coasters, etc, the disks are very fragile. If they are important to us,
they should be treated as such. CDs and DVDs should be stored in cool dry
places that are shielded from large fluctuations in temperature and
humidity, and they should be handled in certain ways with special care.
Fortunately we already have all of the best stroage and care procedures in
place in our field. We just have to make sure they are applied to this
technology in the same way.
We also need to keep in mind that the technology is changing so fast that
there may be radically different and incompatible technologies in place
long before our current disks die, necessitating migration. Always go with
high end disks, because you will definitely get what you pay for. Also
check your disks for functionality immediately after making them. Some
small percentage fail immediately, and it would be unfortunate to discover
that after a couple years when the original data is no longer available.
Storage and how much you use a disk will definitley effect its life, so
only make copies from an archived version, never one you have been playing.
These are also some good sites with other links for your information
http://www.manifest-tech.com/media_dvd/dvd_compatibility.htm
http://www.osta.org/technology/dvdqa/dvdqa11.htm
Here is a forum discussion on the topic at CNET. Some good advice in there.
I hope that is helpful. I would love to what others out there might be
thinking of in terms of policy.
Mark Janzen
Registrar/Collections Manager
Edwin A. Ulrich Museum of Art
Martin H. Bush Outdoor Sculpture Collection
Wichita State University
(316)978-5850
Jennifer Rogers
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Mark,
In response to your statement about DVD's having a lifespan,
do you know how long it is comparable to VHS and other forms of magnetic
storage?
Jennifer C. Rogers, Collections Assistant
Texas Ranger Hall of Fame and Museum
P.O. Box 2570
Waco, TX 76702-2570
(254) 750-8482
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Sent: Thursday, July 21, 2005 4:43 PM
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Subject: Re: [MUSEUM-L] DVD foibles
Ellen,
DVD players definitely have a lifespan. For continuous play, 6 months is
about as long as one could expect to have consistent, quality play, even
with proper cleaning and whatnot. I have burned out two in the past year in
exactly that way. It turns out to be cheaper to buy the 60 dollar versions
every six months, than the multi-hundred dollar professional grade versions
every two to three years. Sometimes you will luck into one that lasts for
much longer. Rather like light bulbs. They may last for a long while, but
when they go they go.
Worn out DVD players can definitely damage disks played in them, both
physically and informationally. If the skips/glitches are always in the
same place then your disk may be damaged, but if they are random it is
likely your player. If new copies of the disk still have glitches when run
in a new player, then the data on your original is faulty for some reason.
The DVDs themselves also have a lifespan, and can begin to lose data in as
little as a year, depending on their quality and material composition.
Continuous play will shorten their lifespan considerably. Make sure to have
an archival(unused) copy of anything you intend to play alot, from which
you make your copies. Do not copy a heavily played disk. If we are talking
about truly valuable archival information or art, then the disk(s) should
be copied every few years, whether or not they are played/accessed.
Essentially, we need to make sure our collections policies include the fact
that CDs/DVDs are not permanent media storage, and they should not be
treated as such.
Good luck.
Mark Janzen
Registrar/Collections Manager
Edwin A. Ulrich Museum of Art
Martin H. Bush Outdoor Sculpture Collection
Wichita State University
(316)978-5850
Ellen Carrlee
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We have a DVD of our local history film that we play continuously in the
summer for our visitors. It gives us glitches, skips, and other troubles
fairly frequently, even if we switch to a new copy or a new TV. I'm
wondering if other institutions play a film continuously and what the
parameters might be for wear-and-tear on the machine or the DVD. Our
situation:
DVD built-in to a TV (from Costco)
DVD on repeat
DVD removed nightly and put in its case
DVD and DVD player cleaned regularly
DVD plays 7 hours per day, 7 days per week
We have only recently switched from using a VCR to show our film and I'm
hoping folks out there might be able to tell us something about our
problem.
Thank you!
Ellen Carrlee
Curator of Collections and Exhibits
Juneau-Douglas City Museum
155 S. Seward Street
Juneau, AK 99801
(907) 586-3572
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