Text 14, 182 rader
Skriven 2004-07-17 07:09:07 av BEN RITCHEY (1:393/68)
     Kommentar till en text av JASEN BETTS
Ärende: Re: cdwriter
====================
* An ongoing debate between Jasen Betts and All rages on ...

 JB: > Is there any special trick to writing CD-RWs I've just been trying to
 JB: > record regular ISO images to them but have had only limited success.

My system (233MHz i586/MMX) has created a couple of coasters over the years,
though it's 99% at 4x (on an idle system). Be sure your system can keep up if
you use the higher speeds. I would limit things to 16x, *maybe* 32x, from what
I've read (at least for Data disks). I use CD-RW quick erase and burn ISOs I
create under Linux without problems, though a full erase every 8-10 writes or
so is a good idea. I use Nero under Win98Se to do the actual burning.

 JB: > been buring with "-speed 4 -blank fast" (or lower speeds) but it
 JB: > seems to get worse the more I try.

AFAIK, you have to blank/erase first, then record, at least I do <shrug>.

FYI, I found this in my docs bin <g>:

=== Cut ===
                          High Speed CD-R Risks

                 Jerome L. Hartke, Media Sciences, Inc.
                  Published in medialine, February 2003


Why High Speed?

Computer users are attracted to fast CPU's, video cards, printers, and
drives like moths to a flame, but do benefits justify the attendant
risks? The first 1X drives reliably recorded 63 minute discs in 1990.
Subsequent high speed CD-R media and writers appealed to professional
duplicators because higher throughput reduces unit cost by amortizing
capital, other fixed expenses, and labor costs over more discs. MP3
collectors and gamers are always fascinated by speed and higher
capacity. Progress from 1X to 16X recording produced exceptional
benefits, while 16X-to-48X gains are more modest. Advantages of
pressing beyond 48X to 52X, or even 56X, may be minimal, while risks
multiply.

High recording speeds place severe demands on both writers and media.
Fast drives are susceptible to vibration because their rotational
velocities may be as high as 12,000 rpm, much greater than 7,200 rpm
for hard drives that operate in a sealed environment with balanced
platters. High speed drives may be incapable of supplying forces
necessary to quickly move pickup head optics. High speed media requires
customized dyes and pregroove geometries in order to avoid excessive
heat buildup during recording. Lastly, internal stresses can result in
disc cracking or even fracture at high rotational speeds.


High Speed Discs

Modification of the dye layer during recording creates marks that
simulate the pits of a replicated CD. This process requires the
external application of energy as determined by the product of laser
power and time. High speed recording requires higher power for a given
energy input because recording time is much shorter. Typical laser
power increases from about 6 mW at 1X to over 40 mW at 48X. Resultant
local heating of the information layer by high power beams can
adversely affect electrical parameters, or may even result in
delamination.

Thinner dye layers help reduce overheating1 because lower recording
energy is required, but low HF signal amplitudes, I3/Itop and I11/Itop,
may result. Very high temperatures can be reduced by using thick
reflective layers as heat sinks1, but cost pressures often dictate thin
metal layers. Thermal isolation of surrounding dye regions can be
improved by modifying the pregroove1, but push-pull may be affected.
Jitter can increase1 when high temperatures from a previously written
mark do not fully subside during transit of a short land. The next mark
is then written into a hot area, and jitter increases because its
resulting location depends on variable cooling times that are
determined by the preceding 3T to 11T land lengths.

Both CD-R substrates and replicas are molded by injecting molten
polycarbonate at the center of the disc. Non-laminar flow in this area,
or separation of the sprue from the hot disc, can create high stresses
near the center hole that are retained in the cooled disc. Short cycle
times resulting from cost constraints increase these center hole
stresses that can induce cracking or even fracture of the disc.


High Speed Drives

Optical pickup heads contain electromechanical components that maintain
proper radial position and focus of the laser beam. These components
are controlled by servo circuits [12]  that must promptly and
accurately compensate for any axial or radial shift of the information
layer. To achieve this, servomechanisms generate corrective forces that
are proportional both to the mass of the component and to the
acceleration of inevitable axial or radial shifts. Disc standards limit
these acceleration values, but may be inadequate because they were
prepared before high speed drives became popular. Since acceleration is
proportional to the square of spindle speed, a given physical shift
produces an acceleration that is 356 that is times greater in a 48X CAV
drive than in a 1X CLV drive (or 2304 times greater in a 48X CLV
drive), increasing the required corrective force by 356 (or 2304)
times, assuming constant mass. Not all high speed writers or readers
may be able to correct physical shifts fast enough, causing offtrack or
out-of-focus conditions that result in write defects and read errors.

Drive components are mounted on a chassis that is suspended from its
mounting frame by vibration isolators. Any disc unbalance [13]  results
in motion of the chassis that is partially buffered by these isolators,
with some residual amount directly affecting the pickup head. Pickup
head vibration in high speed writers may result in momentary offtrack
or out-of-focus conditions that record a permanent defect into the
disc. Vibration can be enhanced by unexpected disc or drive resonant
modes, and by unbalance of the drive's spindle motor.

Radial forces from unbalance are proportional to the square of spindle
speed, being 356 times greater at 48X CAV than at 1X CLV. Disc
unbalance limits may be inadequate because they were established before
high speed drives became popular. Additional unbalance can be created
by disc miscentering. Upon disc loading, the 15.0-15.1 mm diameter
center hole is centered on a tapered cone attached to the spindle
motor, and is then held in position by a magnetic clamp. Some drive
dependent miscentering is unavoidable, resulting in unpredictable
unbalance and excessive vibration at high speeds. Since only a small
portion of the disc's center hole contacts the tapered centering cone,
unbalance forces are highly concentrated at this point, and can cause
severe cracking or shattering of the disc at high drive speeds,
especially if high stress is present near the center hole.

Prior to writing, all recording drives perform optimum power
calibration that adjusts recording laser power to produce a
predetermined beta as calculated from HF amplitudes. High speed writers
must additionally apply special write strategies during recording to
compensate for thermal effects described above for high speed discs.
This compensation is normally based upon three parameters that are
determined by the media manufacturer and encoded in each disc. Two of
these parameters specify the level and duration of an enhanced power
region that initiates every mark. The third parameter specifies an
additional delay that is used only if the mark is preceded by a short
land. Successful recording requires accurate initial determination1 of
these parameters by the manufacturer, product consistency to maintain
their validity, and proper write strategy implementation by high speed
writers.


Conclusions

Increases in CD-R recording speed are accompanied by new risks that can
nullify apparent benefits. Mechanical problems can occur because discs
are manufactured to limits of acceleration and unbalance that were
established when only low speed drives were in use. Low stress disc
center holes are required to avoid cracking or fracture, but may not be
achievable with short molding cycle times. High write power can result
in overheating at high recording speeds unless dye and reflective
layers and pregroove geometries are modified, but such changes may
degrade recorded parameters. Acceptable jitter requires new write
strategies that compensate for high temperatures, but requires
effective action by both media and drive manufacturers.

Issues created by high speed DVD trends parallel those for CD-R, except
that 1r DVD speeds correspond to 3X CD speeds. Successful high speed
recording depends on many subtle measures that must be properly
implemented by both disc and drive manufacturers. Confidence in these
components, and in coordination between their suppliers, requires
careful evaluation [16]  of both high speed media and writers if
predictable interchange is to be achieved. Only a cautious approach can
prevent field failures and unhappy users.


1. High speed recording with organic dyes for CD-R, Dr. Jitka
Brynjolffssen, Organic Media Development Manager, Plasmon, published in
ONE TO ONE, 01-2003, pp 57-58.

------------------------------------------------------------------------
              Media Sciences, Inc. -- Dedicated to Quality

=== Cut ===

--
Be well,

 : Ben   aka cMech    http://bellsouthpwp.net/c/m/cmech617/
 :
 +    WildCat! Board 24/7  (337) 232-4155  33.6kBps 8,N,1
--- GoldED+/DPMI32 v1.1.5-040330 r0405
 * Origin: FIDONet - The Positronium Repository (1:393/68)