INFO
CONCERNING DISC COLORS
Taiyo Yuden produced the original gold/green CDs, which were
used during the development of CD-R standards.
Mitsui Toatsu Chemicals invented the process for gold/gold
CDs.
Silver/blue CD-R's, manufactured with a process patented by
Verbatim, first became widely available in 1996.
Remember the PlayStation was originally released in the
United States on 09/09/95 and before that it was released in Japan.
What this means is that the original CD specs that the
PlayStation used was probably based on the original green media since the blue media
wasn't even available until 1996.
Points to consider:
The color of the CD-R disc is related to the color of the
specific dye that was used in the recording layer. This base dye color is modified when
the reflective coating (gold or silver) is added. THIS MEANS THAT THERE IS
ONLY ONE DYE COLOR. BLUE. Some of the dye-reflective coating combinations
appear green, some appear blue and others appear yellow (gold). Visual differences between
various media types are irrelevant from the standpoint of their actual operation. At 780
nm, where CD-R recorders and CD-ROM readers function, the media are, for all intents and
purposes, indistinguishable from an optical recording standpoint. They all
"look" the same to the devices.
The green-bottom CD-R uses the cyanine pigment. By itself,
the pigment is blue in color, but together with the gold reflective layer, the bottom
appears green. (The old TDK's were gold/green and the bottom was a pretty dark shade of
green)
Green media is more forgiving of marginal read/write power
variations, making them easier to read on some drives.
The blue media is made of azo pigments. Like cyanine, it is
blue in color but unlike the green CD-R it uses a silver reflection layer which gives the
blue color.
On the issue of light reflection here is some technical info
on gold (Phthalocyanine dye) vs green (cyanine dye):
Phthalocyanine dye has a narrower range for writeability
with laser light -- the coherent, tightly focused and precisely calibrated light used in
CD-Recorders. The recommended range of laser power for phthalocyanine dye is 5mW, plus or
minus .5 mW. The range for cyanine dye is 6mW, plus or minus 1mW. This wider power margin
ensures that cyanine media is suitable for a greater range of recording speeds and laser
powers. It further ensures that cyanine 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.
The other reason is that the media defined in the Orange
Book itself, and the drives that were designed to record this media, are based on the
original Taiyo Yuden cyanine disc. Taiyo Yuden cyanine media is the de facto reference
medium for the CD-R industry. Most existing CD Recorders are designed to record to cyanine
media. Some CD players and CD-ROM drives will read discs recorded on cyanine media more
readily and reliably than they will read discs recorded on phthalocyanine media. This
compatibility is tied in with a little-discussed concept known as write strategy.
Compact discs use pits of varying lengths to represent data.
The pits are the same width and depth, but their length and the spaces between them vary.
The shortest pit is a 3T pit, and the longest, 11T. In CD-Recordable, the pits are
replaced by optical marks that, when read by a CD player or CD-ROM drive, appear similar
to the pits in molded CDs. 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.
The Long and Short of It
Cyanine discs use a Long Write Strategy, and phthalocyanine
discs use a Short Write Strategy. That is, a longer laser pulse produces a more accurate
3T optical mark on cycanine media, and a shorter laser pulse creates a more accurate 3T
optical mark on phthalocyanine media. Write strategy, in the currently available
generation of CD-Recordable media and drives, is not adjustable for media type. However, a
group of engineers, called OSJ (Orange Book Study Group of Japan) has 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. This proposal
will soon be implemented by the manufacturers of CD-R media and the manufacturers of CD
recordable drives.
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, writeability, 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.
Bottom Line many companies like TDK have switched to blue
media because it offers all of the same benefits of green media plus it has an ability to
maintain reflectivity for longer periods of time thus is has a longer data life of over
100 years. 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 PlayStation.
Finally 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.
Credits: This is compliation of
articles written by Dana Parker and edited versions of a messages originally posted by
"PSX Pirate" on the PSX
Copy Discussion Forum.
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