14 Mar
2005
14 Mar
'05
3:12 p.m.
Richard Bristol wrote:
(5) I don't burn more than 85% of the capacity
of a DVD. DVDs are a sandwich, lexan (polycarbonate)
on both sides, data layer chemistry in the middle.
The spiral starts on the inside (opposite LP records).
If you leave 3/4" unused at the outside edge, it will
take longer before the Ozone and 02 and other environmental
exposures that attack the data chemistry at the edges
of the lexan sandwitch actually reach your data. So on
a "4.7GB" disk which in real life could hold 4.3GB, I
burn 3.8GB.
Interesting approach.
Curious though ... why do the edges get attacked first? Are the disks
slapped together in some sort of fashion such that there exists a potential
breach at the edges?
14 Mar
14 Mar
4:27 p.m.
In message <6.1.2.0.2.20050314145210.0227d3f8 at popmail.ucsd.edu>
"Eric F." <elf at ucsd.edu> wrote:
Curious though ... why do the edges get attacked
first? Are the disks
slapped together in some sort of fashion such that there exists a potential
breach at the edges?
Think about it - there's a 1" plastic hub in the center, followed by a ridge,
then the data layer. On the outside of the disc there is no plastic hub/ridge
to protect it - maybe 1/16" of "unused" dye, then the data itself.
Also, a lot of the Taiwanese media manufacturers (read: CMC and crew) skimp
on the amount of adhesive and enamel coat they use to seal the discs. That
basically means you end up with a disc that will at best fail early, or at
worst delaminate completely. I had a CMC-made "unbranded" blank that
delaminated in a 24x CD-ROM drive, taking the drive on a one-way trip to
silicon heaven. Truly awful discs.
Later.
--
Phil. | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpem at philpem.me.uk | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.me.uk/ | 48xCD, ARCINv6c IDE, SCSI
... Hey! Your Trakball is upside down!
16 Mar
16 Mar
3:04 p.m.
On Tue, 15 Mar 2005 00:27:12 GMT
Philip Pemberton <philpem at dsl.pipex.com> wrote:
. . . I had a CMC-made "unbranded" blank
that
delaminated in a 24x CD-ROM drive, taking the drive on a one-way trip
to silicon heaven. Truly awful discs.
Sometimes I wonder if the high-speed CD-ROM drives we all enjoy now are
always as good as they're thought to be. I remember my first experience
with a > 4x drive. I was used to the older drives which spin slower,
and the new fast drive 'spun up' like there was a big noisy machine
(there was) inside the PC Case. Perhaps there should be effort spent
on a more reliable grade of CD-ROM technology that emphasizes
reliability and long term life over rip-roaring speed. I can't help but
think that spinning your important archival CDs at a 2x reading speed
would be easier on them than the screaming fast rate most are read at
now.
Would the CMC-made "unbranded" blank have delaminated in a 2x drive?
Probably not. Not that the particular CMC media should be 'championed'
in any way, but spinning things faster is bound to accelerate
deterioriation.
3:53 p.m.
Scott wrote:
Perhaps there should be effort spent
on a more reliable grade of CD-ROM technology that emphasizes
reliability and long term life over rip-roaring speed.
As with all other PC components, there's effectively no market for higher
quality. That is to say, not enough market to justify the engineering,
manufacturing, and marketing efforts that would be necessary. Too many
buyers are willing to put up with marginal junk. This is called a
"trimuph of crapitalism".
Eric
6:12 p.m.
Scott Stevens wrote:
Sometimes I wonder if the high-speed CD-ROM drives we
all enjoy now are
always as good as they're thought to be. I remember my first experience
with a > 4x drive. I was used to the older drives which spin slower,
and the new fast drive 'spun up' like there was a big noisy machine
(there was) inside the PC Case. Perhaps there should be effort spent
on a more reliable grade of CD-ROM technology that emphasizes
reliability and long term life over rip-roaring speed. I can't help but
think that spinning your important archival CDs at a 2x reading speed
would be easier on them than the screaming fast rate most are read at
now.
This is a sound (no pun intended) theory, and Nero comes with software that can
be used to limit the speed of your CDROM drive.
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Want to help an ambitious games project? http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
14 Mar
14 Mar
4:46 p.m.
Eric asks about writable DVD media:
why do the edges get attacked first? Are the disks
slapped together in some sort of fashion such that there exists a
potential breach at the edges?
Yes. They are laminated with adhesive, just as laser videodiscs were.
The adhesive leaks O2 even when it's working well, and as it degrades
it leaks worse.
Laser videodiscs have higher mass, so the problems occur faster, but
there's no reason to expect that the same problems won't happen to
DVD media. With laser videodiscs, the problems do start closer to
the outer edge, but they very rapidly (in a few weeks to a month)
progress to affecting the entire disc. I expect that DVDs will
behave similarly, though not quite as quickly. So not using the
edge will gain you a little, but not a lot. Not enough that you
should reduce your concern by any significant amount.
Eric
6:59 p.m.
Eric Smith wrote:
Yes. They are laminated with adhesive, just as laser
videodiscs were.
The adhesive leaks O2 even when it's working well, and as it degrades
it leaks worse.
Laser videodiscs have higher mass, so the problems occur faster, but
there's no reason to expect that the same problems won't happen to
DVD media. With laser videodiscs, the problems do start closer to
the outer edge, but they very rapidly (in a few weeks to a month)
progress to affecting the entire disc. I expect that DVDs will
behave similarly, though not quite as quickly. So not using the
edge will gain you a little, but not a lot. Not enough that you
should reduce your concern by any significant amount.
But not writing near the edge will help with finger prints.
Also the surface of some CD's can be easly scraped with a finger
nail. I did that trying to get a CD out of a paper sleeve.
Ben alias woodelf.
15 Mar
15 Mar
2:20 p.m.
Ben wrote:
But not writing near the edge will help with finger
prints.
Fingerprints have relatively little effect on CDs or DVDs, because the
laser is tightly focused on the reflective layer, not the surface.
Naturally it is still best to avoid getting figerprints on the disc
as much as possible. I try to handle them only by the hub and outer
rim.
Note that for CDs (but not DVDs), dmage to the top (label-side) surface
of the disk is *MUCH* more likely to cause problems than damage to
the bottom, because the actual data surface is only under a thin layer
of lacquer and silkscreening.
Eric
2:28 p.m.
Eric Smith wrote:
I try to handle them only by the hub and outer
rim.
I handle them only by the rim. I once handled a disc so much by both the hub
and rim that I ended up getting the inner hub so oily (due to contact with my
fingers) over time that it didn't spin at a consistent speed any more as the
hub locking mechanism couldn't get a decent grip on it. It took me over an
hour to figure out why the disc wasn't working consistently. Granted, this was
in 1995-era DOS days, but still...
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Want to help an ambitious games project? http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
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bfranchuk＠jetnet.ab.ca -
chenmel＠earthlink.net -
elf＠ucsd.edu -
eric＠brouhaha.com -
philpem＠dsl.pipex.com -
trixter＠oldskool.org