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A CD-R (Compact
Disc-Recordable) is a variation of the Compact Disc digital audio
disc invented by Philips and Sony. CD-R is a write once, read-only medium
(though the whole disk does not have to be written in the same session)
and retains a high level of compatibility with standard CD readers (unlike
CD-RW which can be rewritten but has much lower compatibility and the
discs are considerably more expensive).
History of the
The CD-R, originally named CD Write-Once (WO),
specification was first published in 1988 by Philips and Sony in the
'Orange Book'. The Orange Book consists of several parts, furnishing
details of the CD-WO, CD-MO (Magneto-Optic), and CD-RW (ReWritable). The
latest editions have abandoned the use of the term 'CD-WO' in favor of
'CD-R'. Written CD-Rs and CD-RWs are fully compatible with the Audio CD
(Red Book) and CD-ROM (Yellow Book) standards. They use Eight-to-Fourteen
Modulation, CIRC error correction plus the third error correction layer
defined for CD-ROM.
The dye materials developed by
Taiyo Yuden made it possible for CD-R discs to be compatible with Audio CD
and CD-ROM discs.
Physical Characteristics of CD-R
A standard CD-R is a 1.2 mm thick disc made of
polycarbonate with a 120 mm or 80 mm diameter. It has a storage capacity
of 74 minutes of audio or 650 MiB of data. CD-R/RWs are also available
with capacities of 79 minutes, 59 seconds and 74 frames (marketed as 80
minutes) /736,966,656 bytes (702 MiB), which they achieve by burning at
the maximum allowable tolerances specified in the Orange Book CD-R/CD-RW
standards. Most CD-Rs on the market have an 80 minute capacity. There are
also 90 minute/790 MiB and 99 minute/870 MiB discs, although they are
rare. Also, due to the limitations of the data structures in the ATIP (see
below), 90 and 99 minute blanks will identify as 80 minute ones and have
to be burned using the 'overburn' options in the CD recording
The polycarbonate disc contains
a spiral groove to guide the laser beam upon writing and reading
information. The disc is coated on the side with the spiral groove with a
very thin layer of organic dye and subsequently with a thin, reflecting
layer of silver, a silver alloy or gold. Finally, a protective coating of
a photo-polymerizable lacquer is applied on top of the metal reflector and
cured with UV-light.
A blank CD-R is not 'empty', it
has a pregroove with a wobble (the ATIP), which helps the writing laser
stay on track and is used to ensure the data is written to the disc at a
constant rate. As well as providing timing information, the ATIP (absolute
time in pregroove) is also a data track containing information about the
CD-R manufacturer, the dye used and media information (disc length etc).
The pregroove is not destroyed when the data is written to the CD-R, a
point which some copy protection schemes use to distinguish copies from an
Among the first CD-R
manufacturers were the companies Taiyo Yuden, Kodak, Maxell, and TDK.
Since then, the CD-R was further improved to allow writing speeds as fast
as 52x (as of 2004) relative to the first 1x CD-Rs. The improvements were
mainly due to optimisation of special dye compositions for CD-R, groove
geometry, and the dye coating process. 40x and higher burners (often part
of a DVD Burner these days) are very common. However while disks burned at
these fast speeds tend to read fine in modern PC drives, audio players
often have trouble reading them. Low-speed burning at 1x is still used for
special 'audio CD-Rs', since CD-R audio recorders were standardized to
this recording speed.
There are three basic
formulations of dye used in CD-Rs:
1. Cyanine dyes
were the earliest ones developed, and their formulation is
patented by Taiyo Yuden. Cyanine dyes are mostly green or light blue in
color, and the earlier models are chemically unstable. This made cyanine
discs unsuitable for archival use; they can fade and become unreadable in
a few years. Many manufacturers like Taiyo Yuden use proprietary chemical
additives to make more stable cyanine discs ('metal stabilized Cyanine',
'Super Cyanine'). Older Cyanine dye based CD-Rs, as well as all the hybrid
dyes based on cyanine, were very sensitive to UV-rays and could have
became unreadable after only a few days if they are exposed to direct
sunlight, however this has become a non-issue with recent developments. A
common mistake users make is to leave the CD-Rs with the 'clear'
(recording) surface upwards, in order to protect it from scratches.
Azo dye CD-Rs are dark blue in color, and their
formulation is patented by Mitsubishi Chemicals. Unlike cyanine, azo dyes
are chemically stable, and typically rated with a lifetime of
3. Phthalocyanine dye CD-Rs are usually
silver, gold or light green. The patents on phthalocyanine CD-Rs are held
by Mitsui and Ciba Specialty Chemicals. These are also chemically stable,
and often given a rated lifetime of hundreds of years. Unlike cyanine,
phthalocyanine dye discs can be less sensitive to UV rays and CD-Rs based
on that may be well read with no signs of degradation, even after a week
of direct sunlight exposure.
There are many hybrid variations
of the dye formulations, such as Formazan by Kodak (a hybrid of cyanine
and phthalocyanine) and Super Azo by Mitsubishi
manufacturers add additional coloring to disguise their cyanine CD-Rs, so
the formulation of a disc cannot be determined based purely on its color.
Similarly, a gold reflective layer does not guarantee use of
The quality of the disc is also not only dependent
on the dye used, it is also influenced by sealing, the top layer, the
reflective layer, and the polycarbonate. Simply choosing a disc based on
its dye type may be problematic. Although the CD-R was initially developed in
Japan, most of the production of CD-Rs had moved to Taiwan by 1998, and
also to Mainland China. Taiwanese manufacturers supplied more than 70% of
the worldwide production volume of 10.5 billion CD-Rs in
The blank disc has a pre-groove track onto which
the data is written. The pre-groove track, which also contains timing
information, ensures that the recorder follows the same spiral path as a
conventional CD. Instead of pressing a CD with indentations, a CD-R writes
data to a disc by using its lasers to physically 'burn' the organic dye.
When heated beyond a certain temperature, the area that was 'burned'
becomes opaque and reflects less light than the areas that have not been
'burned'. Note that the 'burning' process does not produce the
conventional indentations (pits). The reflection modulation can be
detected by a photo-diode. Upon reading back the stored information, the
laser operates at a low enough power not to 'burn' the dye and an optical
pick-up records the changes in the intensity of the reflected laser
radiation when scanning along the groove and over the pits. The change of
the intensity of the reflected laser radiation is transformed into an
electrical signal, from which the digital information is recovered
('decoded'). The decomposition of the dye in the pit area through the heat
of the laser is irreversible (permanent). Therefore, once a section of a
CD-R is written, it cannot be erased or rewritten, unlike a CD-RW. A CD-R
can be recorded in multiple sessions. A CD recorder can write to a CD-R
using several methods including:
1. Disc At Once - the whole CD-R is
written in one session with no gaps and the disc is 'closed' meaning no
more data can be added and the CD-R effectively becomes a standard
read-only CD. With no gaps between the tracks the Disc At Once format is
useful for 'live' audio recordings.
2. Track At Once - data is
written to the CD-R one track at a time but the CD is left 'open' for
further recording at a later stage. It also allows data and audio to
reside on the same CD-R.
3. Packet Writing - used to record data
to a CD-R in packets allowing extra information to be appended to a disc
at a later time or information on the disc can be made 'invisible'. In
this way CD-R can emulate CD-RW however each time information on the disc
is altered more data has to be written to the disc. There can be
compatibility issues with this format and some CD
A rough estimation of the amount
of data on a CD-R can be gained by inspecting the playback side of the
disc. A visible variation in the surface can be observed. CD-Rs are
written from the center of the disc outwards.
storage, expected lifespan of a CD-R and how to clean
At present, stated CD-R lifetimes are only estimates
based on accelerated aging tests as the technology has not been in
existence long enough to verify the upper range. With proper care it is
thought that CD-Rs should be readable one thousand times or more and have
a shelf life of several hundred years. Unfortunately, some common
practices can reduce shelf life to only one or two years. Therefore, it is
important to handle and store CD-Rs properly if it is necessary to read
them more than a year or so later.
Burned CD-Rs suffer from
material degradation, just like most writable media. Optical discs
commonly used for burning, such CD-R and CD-RW have a recording surface
consisting of a layer of dye that can be modified by heat to store data.
The degradation process can result in the data 'shifting' on the surface
and thus becoming unreadable to the laser beam.
As well as degradation of the
dye, failure of a CD-R can be due to the reflective surface. While silver
is cheaper and more widely used, it is more prone to oxidation resulting
in a non-reflecting surface. Gold on the other hand, although more
expensive and hard to find on a CD-R, is an inactive material and so, gold
based CD-R's do not suffer from this problem.
One last factor that affects the
quality of a CD-R and influences its lifespan is the lacquer that is used
to seal the CD-R and protect the dye and the reflective material from the
influence of external materials (air, water, alcohol, etc).
general rule it is recommended that one only clean a CD-R if the playback
is affected. The error correction of CD-R can effectively read through
fingerprints as well as a highly scratched information
The preferred way to remove
excess dust from CD-R is by using canned pressurized clean air. Dust can
also be removed from the information surface by very lightly wiping the
information side with a very soft cloth (such as an eyeglass cleaning
cloth) from the centre of the disc in an outward direction. Wiping the
information surface of any type of CD in a circular motion around the
centre, however, has been known to create scratches in the same direction
as the information and potentially cause data loss.
Fingerprints or stubborn dust
can be removed from the information surface by wiping it with a cloth
dampened with alcohol (methylated spirits or isopropyl alcohol) and again
wiping from the centre outwards, with a very soft cloth.
It is harmful, however, to use
acetone, nailpolish remover, kerosene, petrol (gasoline), or any other
type of petroleum-based solvent to clean a CD-R: the use of petroleum
based solvents will damage the polycarbonate surface and the CD-R will
Another way of cleaning a greasy
CD is by washing it with a mild dish-washing detergent in room temperature
water (~20-35 °C)). With the aid of soft pure cotton only, it is possible
to wash the CD by making radial, but not concentric, soft movements on the
CD surface, and then washing thoroughly with
Ensuring that any water drops on the
surface do not remain, and allowing to dry naturally (not attempting to
use heat to evaporate any moisture, e.g. using a hair-dryer, whose heat
would warp the disk and render it unreadable), one can effectively remove
grease and oil from the surface of the disk. Nevertheless, this method is
not recommended for those unfamiliar with the method, or when dealing with
discs containing especially important data: failure to follow this
procedure correctly could potentially damage the disk.
To remove fingerprints, grease,
dust, and even some very minor scratches, rub toothpaste over the entire
bottom of the CD. Let it sit for 30 to 60 seconds, then hold the disc
under running water and use a radial motion to remove all the toothpaste.
Allow the disc to air dry.
CD-Rs should not be cleaned in a
circular motion due to the nature of the error-correction employed. Small
streaks and scratches that run in a radial direction (perpendicular to the
spiral track) create numerous tiny errors but which are easily corrected
due to the redundant Reed-Solomon correction information surrounding the
error. Streaks and scratches that run parallel to the track will cover a
significant portion of the track all at once, including the surrounding
codes, which cannot be corrected and will result in skipping and
Wikipedia information about
CD-R. This article is licensed under the GNU Free Documentation License . It uses material
from the Wikipedia article 'CD-R'
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