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CD - R

• a variation of the Compact Disc invented by Philips and Sony.

• a Write Once Read Many (WORM) optical medium.

• needs to allow the drive to write data onto the disc.

In a normal CD, you have a plastic substrate covered with a reflective aluminum or gold layer.

In a CD-R, you have a plastic substrate, a dye layer and a reflective gold layer.

The dye is fairly sensitive to light -- it has to be in order for a laser to modify it quickly.

Therefore, you want to avoid exposing CD-R discs to sunlight.

Recording a CD is called "Burning".

Data is actually burned into the CD with a laser.

Once the data is burned into it, it is there to stay. The same however is not the case for the CD-RW media.

Sanyo’s HD-Burn - doubles the recording capacity and data density (1.4GB) of a conventional CD-R media (700MB). This technology enables inexpensive large volume data recording .

Plextor’s Gigarec - Increases storage capacity by 40%, allowing up to 1GB on a 700MB disc.

A standard CD-R is a 1.2 mm (0.047 in) thick disc made of polycarbonate with a 120 mm (4.7 in) or 80 mm (3.150 in) diameter. A120 mm disc has a storage capacity of 74 minutes of audio or 650 MB of data.

Most CD-Rs on the market have an 80 minute capacity. There are also 90 minute/790 MB and 99 minute/870 MB discs, although they are less common

Due to the limitations of the data structures in the ATIP(Absolute Time in Pregroove) 90 and 99 minute blanks will identify as 80 minute ones.

Therefore, in order to use the additional capacity, these discs have to be burned using "overburn" options in the CD recording software.

The polycarbonate disc contains a spiral groove, called the "pregroove" (because it is molded in before data are written to the disc), to guide the laser beam upon writing and reading information.

The pregroove is molded into the top side of the polycarbonate disc, where the pits and lands would be molded if it were a pressed (nonrecordable)

The polycarbonate disc is coated on the pregroove side with a very thin layer of organic dye.

Then, on top of the dye is coated 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.

1. Cyanine dye CD-Rs were the earliest ones developed, and their formulation is patented by Taiyo Yuden. CD-Rs based on this dye are mostly green in color. • This could 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 become unreadable after only a few days if they were exposed to direct sunlight. Although the additives used have made cyanine more stable, it is still the most sensitive of the

2. 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.

• Phthalocyanine is a natively stable dye (has no need for stabilizers) and CD-Rs based on this are often given a rated lifetime of hundreds of years.

• Unlike cyanine, phthalocyanine is more resistant to UV rays and CD-Rs based on this dye show signs of degradation only after two weeks of direct sunlight exposure.

3. Azo dye CD-Rs are dark blue in color, and their formulation is patented by Mitsubishi Chemical Corporation.

• Azo dye is also chemically stable, and Azo CD-Rs are typically rated with a lifetime of decades.

• Azo is the most resistant dye against UV rays and begins to degrade only after the third or fourth week of direct sunlight exposure.

where the data are written.

contains timing information, ensures that the recorder follows the same spiral path as a conventional CD.

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:

•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. It is useful for "live" audio recordings.

•Track At Once – data are 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.

•Packet Writing - is an optical disc recording technology used to allow write-once and rewritable CD and DVD media to be used in a similar manner to a floppy disk from within the operating system, i.e., it allows users to create, modify, and delete files and directories on demand without the need to burn a whole disc. Packet writing technology achieves this by writing data in incremental blocks rather than in a single block