A computer components & hardware forum. HardwareBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » HardwareBanter forum » General Hardware & Peripherals » General
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

When Good Discs Go Bad



 
 
Thread Tools Display Modes
  #1  
Old June 27th 04, 03:47 AM
Ablang
external usenet poster
 
Posts: n/a
Default When Good Discs Go Bad

Burning Questions
Associate Editor Melissa J. Perenson delves into the world of optical storage,
offering reviews and practical tips.



When Good Discs Go Bad

Ever wonder what makes a disc bad? Here's why they vary in quality, and why you
should worry about the discs you've entrusted with your data.


Melissa J. Perenson, PC World
Tuesday, June 15, 2004
Burning CDs and DVDs is the easy part.

Knowing your data will be there when you go back to it days, months, or even
years later--well, that's a bit harder. Not all discs are created equal, as
Fred Byers, information technology specialist at the National Institute of
Standards and Technology, can attest.

Byers is part of a team heading up an independent study of DVD media quality.
Based on the first wave of testing results, the situation is murky at best.

"We've found the quality varies, depending upon the type of dye used to make
the write-once discs and [on the] the manufacturer," reports Byers. Even discs
from the same manufacturer, with the same brand, can test differently, Byers
adds. "But there was more of a significant difference when you compared discs
between manufacturers," he explains.


DVD Media Quality: The First Tests
In the first phase of testing, completed late last year, NIST focused on the
most popular media: write-once, single-layer DVD-R and +R discs. Rewritable
discs will be tested in the second phase, slated to start this fall. An
interesting footnote to the study's methodology: NIST uses media purchased off
store shelves and via Web sites; and while researchers are tracking the media
by brand, they are not tracking the specific factory source of the media
tested. For example, a given manufacturer's discs could originate from
different production lines, which could account for a variation in disc quality
by the same manufacturer.

Hearing that there's a difference between the generic, unbranded 100-spindle
value-pack of media purchased online and the branded offerings you might find
on a Best Buy store shelf is not surprising. After all, as David Bunzel,
president of the Optical Storage Technology Association, points out: "With a
generic product, there's no consumer recourse. It's buyer beware."

If a disc isn't properly manufactured, the consequences can be dire. At best,
the disc will fail immediately during the burn process; this is a best-case
scenario because then you know from the start that the disc is faulty. At
worst, you may get an abundance of errors during the burn process. These errors
won't interrupt the burning process, and since write-once and rewritable DVD
media have built-in error correction to compensate for scratches and other
abnormalities on the disc (as do their CD cousins), any errors will be
virtually invisible to you. You'll only know they're there if you use a disc
diagnostics program, such as those offered by Ahead Software or Plextor. Nor
will these errors affect the playback of the disc--initially.

Down the road, however, such invisible-to-the-eye errors can reduce the
effectiveness of a DVD's built-in error correction so that if some other issue
develops on your disc, such as a scratch, you could end up with an unreadable
disc when you go back to it months or years later.

But what would cause such a wide disparity in media quality between branded
discs from the same vendor?

"We don't know why it's different--it could be a different dye, it could be a
different manufacturing process," notes Byers. "Manufacturers are constantly
trying to improve their dye formulas--in theory improving the disc."

Nonetheless, at the same time, competitive forces are driving manufacturers to
find ways to economize on production costs. And cost-cutting measures can
result in discs that don't perform as well as those generated during an earlier
production run, either in terms of failing outright or not burning at the
maximum possible speed on a given DVD drive. "It varies over time, as the
output changes," Byers says.


Brand Disparity
As for the disparity between brands that NIST found, the distinguishing factors
come down to quality control and the dyes used in disc production. Declining to
name names, Byers points out that "some manufacturers make their own discs, and
some purchase them from someplace else--which opens you to variations in the
manufacturing plant, or changes in the source [of that media]."

Vendors like Maxell and Verbatim manufacture discs on their own production
lines, as do Asian manufacturers CMC Magnetics, RiData, Taiyo Yuden, and
others; other name brands contract with a third-party manufacturer to produce
discs to their own specs; and still others just buy third-party-produced media
wholesale, without imposing their own set of quality controls on the media
production.

The intricacies of disc production and quality control aren't the only
variables that seem to affect media. More surprising is the number of discs
that seem to have a propensity for specific hardware.

"One thing we've found in compatibility testing [of DVD-R and +R media] is that
it's a relationship between a specific brand of media and the manufacturer of
the hardware," observes Byers. "There was no one drive that played every single
type of compatible media, and there was no one media brand that played
perfectly in every drive."

And, he adds, sounding as frustrated as any consumer might, "You can't say
there's a clear, delineated set of reasons as to why."


A Grading System?
One of the most common questions I hear is, "What's a good brand of media to
buy?" DVD and CD media are so commonplace nowadays that it's easy to forget the
complexities that go into producing them. And if anything in that production
process is off, it could, in time, affect the integrity of the data you've
burned to a disc.

"It's very tough to answer that kind of question, because there are so many
variables," says Byers. "You don't get 100 percent yield when you manufacture
these discs. We can talk about the materials that produce a good disc, but it
also has to do with the manufacturing process. So, just to say the materials to
look for doesn't necessarily relate to it being a better disc." The same is
true vice versa.

So how can you know that the media you're using will last you for the duration,
so those archived photos will still be there when you go back to a disc 20
years from now--or more?

For the moment, you can't. All DVD and CD vendors make vague claims about disc
life expectancy being somewhere between 60 and 100 years--when the discs are
treated with care and stored properly.

But NIST's Byers is seeking to change that. At an OSTA meeting in San Francisco
this week, Byers is proposing an industry-wide grading system to indicate disc
quality.

Byers is motivated by the desire to see a uniform mechanism in place to guide
institutions and individuals who'll be storing data, music, videos, and images
for long periods of time. "They need to be confident in their purchasing, so
they can plan for their strategies in storing their information," Byers says.
"Long-term storage has different meanings: For some, 30 years might be enough.
For others, 50 or 75 years might be archive, or long-term, quality."


Longevity
Under Byers's proposal, a series of tests would be developed to determine
whether a DVD would last for a given number of years. "If you were to purchase
a disc in a store with a grade that indicates it has passed a test to last X
number of years, it removes a lot of uncertainty for the consumer, and it can
save some expense in premature migration [to a new storage technology], or loss
of data because they waited too long [and the disc was no longer playable]," he
says.

Although some archivists--both individual and professional--are concerned about
whether today's digital storage mediums will be readable 50 or 100 years from
now, Byers believes the bigger concern for users will be when to migrate their
data to the next technology, "before the existing technology is obsolete."


The Disc Rot Myth
Media obsolescence isn't the only thing people fear after committing a personal
library's worth of data to CDs and DVDs. But some worries--namely, fear of disc
rot--are not fully warranted.

Like a bad seed, the myth of disc rot self-perpetuates, cropping up every now
and again as a sudden and mortal threat to your copious collection of
prerecorded and self-created discs.

The myth was once rooted in fact. It is true that back in the 1980s, with the
first generation of prerecorded audio CDs, the edges of the discs were not
always sealed properly, which allowed moisture to get into the disc.
Replicated, prerecorded discs use aluminum for the reflective layer; when
moisture came into contact with the aluminum on prerecorded discs, explains
Byers, it in turn oxidized, causing the aluminum to become dull. "That's where
the term 'rot' started," he says.

But that problem was quickly identified and overcome. "The manufacturers
learned what was going on, so now the edges of discs are sealed with a
lacquer," according to Byers. Though the problem is typically associated with
CDs, Byers notes that the potential for interaction with oxygen is the same
with both CD-ROMs and DVD-ROMs.

The so-called rot issue does not apply to recordable discs. For one thing,
recordable optical media do not use aluminum; instead, they use silver, and
very rarely gold, or a silver-gold alloy, for the reflective layer. "If the
silver comes into contact with sulfates [i.e., pollution, or high humidity], it
could affect the silver, but the likelihood of that is less than the likelihood
of moisture coming into contact with the aluminum on prerecorded discs," says
Byers.


Enduring Myth
The term rot has persisted, however inaccurately, as a means of identifying a
plethora of problems with optical discs. "If you get a faulty disc and see a
problem that you can visually see, you call it rot, but it could be the way the
disc was manufactured," says Byers. "Or if it was subjected to extreme moisture
and that moisture came into contact with the aluminum, it could be that the
reflectivity has changed. It's not really rot, it's oxidation of aluminum. It
should be a rare event on a disc, unless it's defective."

Beyond the realm of defective discs, improper handling can cause otherwise good
discs to go bad. Since there's little protection between the label side of a CD
and the data layer itself, "scratches on the label side can scratch the metal,
and that will ruin the data," says Byers. It's not an issue for DVDs, though,
since the dye layer is sandwiched between two plastic layers.

Byers observed a similar problem occurring with press-on labels: "For long-term
storage, we recommend not using press-on labels on CDs; when these start to dry
up, they can peel the metal right up, damaging data."

Have you experienced oddities with CDs and DVDs--whether you've recorded them
yourself, or purchased them years ago? If so, tell us your story--including
what kind of disc it was, when the problem first surfaced (and during what
activity), how old the disc was.

http://www.pcworld.com/news/article/...061504X,00.asp

==
"It takes less time to do a thing right than to explain why you did it wrong."
-- Henry Wadsworth Longfellow
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
can anyone confirm? computer resets when loading winx, not softw, one bad address when testing good ram on this machine General 0 June 22nd 04 04:44 PM
Lexmark Laser Printer, good choice over HP and Brother? Miguel Angel General 2 May 20th 04 01:37 PM
Are 19" Princeton LCD any good? cyber General 0 March 17th 04 05:26 AM
Good Deals Online Jeroen General 3 December 7th 03 08:48 AM
3COM Ethernet is "good" - huh? Crusty \(-: Old B@stard :-\) General 6 September 17th 03 01:02 AM


All times are GMT +1. The time now is 09:59 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 HardwareBanter.
The comments are property of their posters.