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Let's
Get Technical About It, Shall We?
The following information is what I've learned in my
'ventures' around the internet, in reading articles and posts, and by asking questions of
manufaturers. If you're really interested in why some media will work better than
others of the same color, read on...
The first thing you have to understand is how CD's read
data. A CD-ROM drive 'reads' CD's with its laser. As it scans the disc,
it 'sees' pits (or 'nicks') in the disc. It then interprets these pits as data.
What the CD-R drives do is 'burn' optical marks onto CD-R media that, when read by
a CD-ROM drive, appear to look like normal pits. The CD-R drive has a special laser
that heats up and 'burns' the disc with these pits. This is why you can't fix a
mis-burned CD-R - once the area has been 'burned', it has been changed permantely.
Now, the actual pits themselves are always the same width
and depth, but they are are of varying lengths - the shortest is a "3T pit", and
the longest is an "11T pit". The length and the spaces between the pits
varies, and this is what makes up the data on the disc.
A CDs that is professionally reproduced is not like the one
you burn at home. These discs are pressed by a pressing machine, which creates
physical pits in the disk. The entire disc is written at once in about two seconds using
this method. It is impossible to truly pit a disc at home, so the laser burns a mark that
replaces the pit. The lengths of the pits or marks are time-relative, not absolute; that
is, the length is a function of disc spin. A disc that spins at a rate of 1.2 m/s while
being recorded will contain marginally shorter 3T to 11T pits than a disc that spins at
1.4 m/s. It will also contain more of them, which allows for greater disc capacity, but
that's a topic for another day.
Using laser light to create a microscopic mark of a certain length on dye polymer is not a
linear process. Because materials tend to respond differently when they are heated for
different lengths of times, a laser setting that produces a light pulse that creates a
mark of a given length does not necessarily produce a mark twice as long when the light
pulse is twice as long. Similarly, a laser setting that produces a light pulse that
creates a mark of a given length in one type or brand of media does not necessarily create
a mark of that same length in another type or brand. This problem is compounded by the
reading drive's pickup; optical effects can alter the perceived length of a mark, so that
what has been recorded may not be the same as what is read. The results of this
discrepancy between what is read and what was intended to be written can vary from
unreadable discs, to discs with a high rate of errors due to jitter. To compensate for
this, recorders can selectively boost or shrink the lengths of individual marks by using a
write strategy. This effectively modifies the pit length signature of a recording medium
so that the detected signals correspond to the input data patterns.
This is the explination behind why a disc might be read just
fine when burned at 2X, but not at all when burned at 4X. The better quality media
can 'take' a 4X burn better than a piece of lower quailty media.
The Long and Short of It
Everyone knows that CD-R discs come in three basic colors: blue, green and gold.
This is the BOTTOM of the disc, not the top! The top's color doesn't matter
too very much - it just helps the reflectivity of the disc in general. The greens
have been around the longest, followed closely by gold. The blues were created by
Verbatim back in 1996.
Now, the green media uses cyanine dye in their discs.
The blues use phthalocyanine dye, and the golds use PhtaloCyanine dye. Green discs
use what is referred to as a "Long Write Strategy" (a longer laser pulse
produces a more accurate 3T optical mark on green media), and the blue discs use a
"Short Write Strategy" (a shorter laser pulse creates a more accurate 3T optical
mark on blue media). Now, for a long time the CD-R drives did not have the
capability to adjust its strategy depending on the media it was using - what this means is
most CD-R drives out there either use the Long Write or the Short Write Strategy, and it's
not something that you can adjust. So if your drive is suted for a Long Write
Strategy, it will probably have more success with green/gold media, wherein if your drive
is suted for Short Write Strategy, it will probably have more success with blue media.
A group of engineers called OSJ (Orange Book Study Group of Japan) proposed that
all CD-R media manufactured include information in the pregroove of the disc that
identifies the type of media and tells the CD Recorder which write strategy to use.
The only CD-R drives that I know of that actually takes advantage of this are all made by
Plextor - the PlexWriter 4/12, 4/20 and the 8/20. (If you know of more, please e-mail me).
If you haven't already been able to tell, CD recordable
technology is a complex and convoluted subject. There are many factors that come into play
when recording a disc: the rate of spin, the formula of the dye, the ambient temperature,
the internal temperature, the age of the media, the power and wavelength of the laser, the
spacing and size of the marks on the media relative to the speed of the disc, to name but
a very few. Media manufacturers are constantly adjusting the myriad factors of disc
production, including but certainly not limited to the formula of the dye polymer. CD-R
media must combine the properties of compatibility, writability, readability, and data
longevity. To say that a certain dye formula or brand of media is inherently better than
another based exclusively on one of these properties is not only simplistic, it is
misleading. This is why you may find that x-brand works better than a Verbatim Data
Life Plus in your drive. So don't take what anyone has to say for gospel in this
industry!
Now, the writing strategy isn't the only thing that makes the disc colors differ from one
another. Green media is 'more forgiving' of burns than blue is (so is gold).
You see, the recommended range of laser power for blue dye is 5mW (miliwatts), plus or
minus 0.5 mW. The range for green dye is 6mW, plus or minus 1mW. This wider power margin
ensures that green media is suitable for a greater range of recording speeds and laser
powers. It further ensures that green media offers a higher likelihood of
compatibility with more CD recorders. There are two reasons for this, one of which has to
do with the possibility that the writing laser may gradually lose power or accurate
calibration over its lifetime. However, the down side to green media is that it's
not as reflective as blue and gold media, so it's harder for the PSX laser to read it.
There's another major difference in the media as well - the
lifespan. Green dye will last appoximately 10 years, where the blue and gold stuff
will last about 100 years. Of course, none of this is going to matter anyway because
in 10 years, who's going to still be using a PlayStation? (How many of you still use
your Atari? It's 10-15 years old now!) And on the other side of the coin, how
many of us are going to be alive in 100? So that really doesn't matter too much.
All media isn't created the same. Just because a
certain brand has a blue bottom doesn't mean its the same quality as TDK or Verbatim
blues. On the other hand just because Maxell gold's may be bad for many doesn't mean
Mitsui gold's won't work as many people have reported to use them successfully on
PlayStations. Personally, I have had great luck recording on Maxell CDR-74P's
(gold/gold) with an Ricoh CD-R at 4X speed. But on the other hand, I know people who
won't touch those CD-R discs with a ten foot pole.
Finally, and most importantly of all, the performance of any piece of media is
always a combination of the disc, the drive that recorded it, and the drive that reads it.
It is rare that the media itself will play the critical role in deciding which backups are
successful and which are not. So don't be afraid to experiment. Go to your
local store and buy a 10-pack of each kind of media, and see which ones do and don't with
your particular setup. After you find out which ones work and which ones don't, buy
the cheapest of the ones that work. And if you really can't afford to do that, just
stick with either Verbatim Data Life Plus, TDK, KAO or Kodak Gold's. You probably
won't have any problems with any of those brands, no matter what setup you're running.
Comments on this? EMail
them to me!
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