March 29, 2007

CD and DVD Format

CD (Compact Disc):

An optical disc. CD is a term loosely used when describing a variety of compact disc formats, from the production (mass-produced) audio and data discs, to the write-once “recordable” versions (CD-R) or write-many "rewritable" versions (CD-RW) CDs. The standard CD can hold about 650MB of data.

CD+G (Compact Disc plus Graphics):

Primarily used for karaoke, this type of CD embeds graphical data with the audio data, allowing video pictures to be displayed periodically
as music is played. A special player is needed to read and display
the information.

CD-I (Compact Disc-Interactive):

A compact disc format designed to allow interactive multimedia applications
(digital audio and video, video games, and software applications)
to be run on a player attached to a television.

CD-R (Compact Disc-Recordable):

A version of CD on which data can be recorded but not erased. An organic dye-based material is used to hold data that are written to it by a laser.

CD-ROM (Compact Disc-Read Only Memory):

An extension of the compact disc digital audio format that allows computer data to be stored.
CD-ROM drive:

A peripheral device attached to a computer that allows it to read and play all CDs.

CD-RW (Compact Disc-ReWritable):
A version of CD on which data can be recorded and erased and re-recorded in the same physical location of the disc. A phase-changing metal alloy film is used to hold the data that are written to it by the laser.


Once stood for Digital Video Disc or Digital Versatile Disc, now just DVD. The next generation of optical disc storage technology after the CD. A DVD is the same physical size and shape as a CD, but has a higher density and gives the option for data to be double-sided or double-layered in the disc.


An audio-only storage format similar to CD-Audio. DVD-Audio differs, however, in offering 16, 20 and 24-bit samples at a variety of sampling rates from 44.1 to 192KHz, compared with 16 bits and 44.1KHz for CDs. The latest audio format more than doubles the fidelity of a standard CD. DVD-Audio discs can also contain music videos, graphics, and other information.

DVD-R (DVD-Recordable, sometimes referred to as DVD minus R):

A version of DVD on which data can be recorded, but not erased, by a disc drive. An organic, dye-based material is used to hold data that are written to it by a laser. DVD-R provides secure recording for volumes of information that cannot be accidentally or intentionally altered. DVD-R has a capacity of 4.7 GB. There are two versions of DVD-R:

1. DVD-R (A) (DVD-Recordable for Authoring):
A format for professional content developers and software producers.
Primarily used to create master discs that will be mass-produced by software houses and multimedia/video postproduction facilities.

2. DVD-R (G) (DVD-Recordable for General use) and DVD+R (DVD plus Recordable):
A format for general recording of all types of content: audio, video, and data. Compatible with most DVD-Video players and DVD-ROM drives.
The differences between DVD-R and DVD+R are as follows:
—DVD+R uses a different technique from DVD-R in how the laser follows the disc track while writing data to the disc. A writer disc-drive is generally capable of writing to one type of disc but some may be capable of writing to both types. All DVD drives should read both DVD-R and DVD+R.
—DVD-R uses constant linear velocity (CLV) for the disc rotation; DVD+R can use CLV or constant angular velocity (CAV) for the disc rotation. CAV allows for easier random access of data on the disc.
—DVD+R can provide lossless linking of new data added from multiple
recording sessions.

DVD-RAM (DVD-Random Access Memory):

A rewritable DVD. It is a cartridge-based, or, more recently, cartridge-
less optical disc for data recording and playback. Data can be recorded and erased up to 100,000 times, making the DVD-RAM a virtual hard disk. DVD RAM uses a phase-change data layer to record data written to it by a laser. Current DVD-ROM drives and DVD-Video players cannot read DVD-RAM media.

DVD-ROM (Read Only Memory):

Typically, an optical disc used for storing data, interactive sequences, audio, and video. DVD-ROMs run in DVD-ROM, DVD-R, DVD-RW, or DVD-RAM drives, but not in DVD-Video players connected to televisions and home theaters. However, most DVD-ROM drives will play DVD-Video movies if the associated software is installed in the computer.

DVD-RW (sometimes referred to as DVD minus RW, DVD-ReWritable):

The DVD-RW is similar to DVD-RAM except that its technology features
a sequential read-write access more like a phonograph than a hard disk. Its read-write capacity is 4.7 GB, and it can be re-written to about 1,000 times. For general recording of all types of content, for audio, for video recording and editing, and for random data recording.
Compatible with most DVD-Video players and DVD-ROM drives.

DVD+RW (DVD plus RW), (DVD-ReWritable):

For general recording of all types of content, for audio, for video recording and editing, and for random data recording. Compatible with most DVD-Video players and DVD-ROM drives.
Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 33
The differences between DVD-RW and DVD+RW are as follows:
—DVD+RW uses a different technique from DVD-RW in how the laser follows the disc track while writing data to the disc. A writer disc-drive is generally capable of writing to one type of disc but some may be capable of writing to both types. Most newer DVD drives should read both DVD-RW and DVD+RW.
—DVD-RW uses constant linear velocity (CLV) for the disc rotation; DVD+RW can use CLV or constant angular velocity (CAV) for the disc rotation. CAV allows for easier random access of data on the disc.
—DVD+RW can provide lossless linking of new data inserted or added from multiple recording sessions.

DVD Video:

Used for viewing movies and for other visual entertainment, DVD Video is a popular format for high-quality MPEG2 or MPEG4 video and digital surround sound. It enables multilanguage, multisubtitling,
and other advanced user features. The total capacity is 17 GB if two layers are used on both sides of the disk.

CD and DVD Lifetime and Maintenance

Life of the medium

The life expectancy (LE) of optical discs depends on many factors, some controllable by the user, others not.
Factors that affect disc life expectancy include the following:
• type
• manufacturing quality
• condition of the disc before recording
• quality of the disc recording
• handling and maintenance
• environmental conditions
As noted previously, the three basic types of CD and DVD discs—ROM, R, and RW and RAM—each use a different data layer material (molded aluminum, organic dye, or phase-changing film, respectively). Deterioration of this material is the primary cause for disc degradation and, ultimately, “end of life” for the disc, assuming proper physical handling.

Environmental factors can affect the rate of disc degradation. In each of the three basic disc types, environmental forces will degrade the data layer much faster than the polycarbonate substrate layer (the clear plastic that makes up most of the disc). Because degradation
of the data layer will render the disc useless well before the polycarbonate begins to deteriorate, the relative degradation rate for the polycarbonate layer is not used for life expectancy considerations.
Physical mishandling of the disc is usually the cause of polycarbonate
layer damage. The polycarbonate may also flex or bend if stored for a long period of time in a nonvertical position.
So what is the life expectancy of a disc? First, we must define life expectancy. For most users, it means the length of time for which the disc remains usable. But that implies some acceptable amount of degradation.

How much and what type of degradation is acceptable?

With CDs and DVDs, the user does not notice early degradation because the error detection and correction capability built into the system corrects a certain number of errors. The user notices a problem only when the error correction coding is unable to fully correct the errors.One method for determining end of life for a disc is based on the number of errors on a disc before the error correction occurs. The chance of disc failure increases with the number of errors, but it is impossible to define the number of errors in a disc that will absolutely cause a performance problem (minor or catastrophic) because it depends on the number of errors left, after error correction, and their distribution within the data. When the number of errors (before error correction) on a disc increases to a certain level, the chance of disc failure, even if small, can be deemed unacceptable and thus signal the disc’s end of life.

Manufacturers tend to use this premise to estimate media longevity.
They test discs by using accelerated aging methodologies with controlled extreme temperature and humidity influences over a relatively short period of time. However, it is not always clear how a manufacturer interprets its measurements for determining a disc’s end of life. Among the manufacturers that have done testing, there is consensus that, under recommended storage conditions, CD-R, DVD-R, and DVD+R discs should have a life expectancy of 100 to 200 years or more; CD-RW, DVD-RW, DVD+RW, and DVD-RAM discs should have a life expectancy of 25 years or more. Little information
is available for CD-ROM and DVD-ROM discs (including audio and video), resulting in an increased level of uncertainty for their life expectancy. Expectations vary from 20 to 100 years for these discs.

Few, if any, life expectancy reports for these discs have been published by independent laboratories. An accelerated aging study at NIST estimated the life expectancy of one type of DVD-R for authoring
disc to be 30 years if stored at 25°C (77°F) and 50% relative humidity.
This testing for R discs is in the preliminary stages, and much more needs to be done.

Individual Disc Storage

Optical discs should be kept in individual storage containers until used and returned to those containers immediately thereafter. Typical
storage containers, as listed below, isolate and help protect discs from airborne contaminants and other foreign material. They also help buffer rapid environmental changes that can cause stresses to the disc. Cases are designed to keep surfaces of the disc from contact with the inside of the case. Only one disc should be placed on the hub (or each hub) in the case. To remove the disc, one should press down on the hub tab while holding the outer edge of the disc with the fingers and then lift up. Bending the disc while lifting it off the hub tab should be avoided.
For long-term disc storage, it may sometimes be prudent to remove
the label insert or booklet from inside the case and attach it to the outside, perhaps in a sleeve. In theory, the paper can attract moisture
and produce higher moisture content in the case. The paper may also spread moisture by contact with the disc. This recommendation is based on no specific tests of the effects of paper inside a case; it is merely a consideration—one that takes on added significance with large amounts of paper inside a disc case and higher-than-recommended
humidity conditions.
Cases commonly used for individual disc protection include the following:
• Jewel case. The jewel case, which comes in different varieties, holds one to six discs, depending on its design. It is typically a transparent
plastic case with a hinged lid, one or more plastic trays, an inlay card for labeling, and an optional booklet.
• Slimline case. As its name suggests, a slimline case is a slimmer version of the jewel case but without the tray. It comes with an inlay
card (J-card) and is primarily used for audio discs.
• Amaray case. An amaray case is a plastic case used for commercially
available prerecorded (replicated) DVD videos and games.
• Snapper case. An alternative to the amaray case, the snapper case is a plastic DVD case with a cardboard cover that is snapped shut and held in place by a plastic lip.

Scratches on the Laser-Reading Side of CDs and DVDs

Scratches generally cross data lines or tracks on the disc, and how bad (deep and wide) they are will determine the extent of interference
with laser focus on the data. Small or occasional scratches will likely have little or no effect on the ability of the laser to read the disc, because the data are far enough below the surface of the disc that the laser is focused beyond the scratch. This is comparable to the effect of a light scratch on a pair of eyeglasses; it does not markedly impair vision because the viewer’s eyes are focused beyond it.
Even assuming a scratch is deep or wide enough to influence laser
focus, error detection and correction coding in the disc drive can in many cases recover the misread data. However, scratches that are deep, wide, or bunched together can adversely affect the readability of the disc. These scratches can cause the laser to misread enough data to make error correction coding ineffectual.
While data errors generated from scratches that run outward from the center of the disc stand a good chance of correction by the error correction firmware, scratches running in the direction of the track, the same direction as the laser reads the disc, are more likely to cause uncorrectable errors. These uncorrectable errors are called E32 in the Red Book for CD specifications, and PO Error in DVD specifications.
If scratches are deep enough to damage the data or metal layers on the reading side of a disc, the data cannot be read or repaired.

Fingerprints, Smudges, Dirt, and Dust

Fingerprints, smudges, dirt, or dust on the laser reading side of the disc can disrupt laser focus on the data even more than a scratch can. Dirt or dust on the disc will block or reduce the light intensity of the laser. If severe enough, it will cause the disc drive to miss data as the disc is being read. Fingerprints, smudges, or dirt cover wide areas of data and will cause the laser beam to go out of focus or lose intensity. They will also cause widespread misreading of data along the data lines or tracks, to an extent that exceeds the error correction capability
of the disc drive. Dust can also spin off into the disc drive and collect on the laser head or other internal components. Fingerprints, smudges, and dirt are easier to remove than scratches; it is simply a matter of cleaning them off.
To summarize, the effects of scratches versus fingerprints and smudges on the laser reading side of a disc include the following:
• Occasional fine scratches will typically not affect the focus of the laser.
• Deep scratches can affect the focus of the laser and cause errors.
• The error detection and correction coding system in the disc drive will correct many errors caused by scratches.
• Fingerprints and smudges can cause more errors than scratches and are more likely to overwhelm the error correction coding system
• Scratches in the direction of the track (tangential direction) are worse than those going from the center of the disc outward (radial direction).
• Like fingerprints and smudges, several scratches close together can also overwhelm the error correction coding system capability.

Wear from Disc Play

CDs and DVDs do not wear from friction as vinyl records or tapes do. There is no physical contact with the disc in the area that the laser
ROM Discs: The laser light will have no effect on the data or metal layer in ROM discs. In theory, it is possible for the disc to be read so many times that the cumulative effect of the laser light can eventually affect the polycarbonate. There is, however, no record of such discs having been played a sufficient number of times to incur damage from laser light. Accordingly, it is felt that any effects of the light on ROM discs is negligible. It is assumed, in fact, that the disc would likely fail much earlier from some other condition than from the effects of laser light.
R discs: In theory, R discs should have a limited number of read times (several thousand) because of the cumulative effect on the data layer from the laser light. As with ROM discs, the polycarbonate may also eventually be affected, but there is no recorded evidence of ill effects of laser light, so such effects are deemed negligible.
RW discs: RW discs, unlike the other types, can “wear-out.” CD-RW and DVD-RW discs should last for about 1,000 rewrites, and DVD-RAM discs, 100,000 times, before the rewriting capability is lost. The reading functionality of the disc should continue for a limited
number of read times after each writing. While the maximum number of read times possible after writing is unknown, it may become
fewer after each successive writing.


CDs or DVDs do not require routine cleaning. It is best to clean the disc only when it is absolutely necessary, specifically:
• before storing, when surface contamination is visible
• before recording, when surface contamination is visible
• before playing, to prevent surface contamination from being “flung off” while the disc is spinning in the disc drive
• when readability (playability) is impaired and surface contamination
is visible
In general, avoid using organic solvents. Harsher solvents (acetone,
benzene) will dissolve the polycarbonate and damage the disc beyond repair. Mild solvents (isopropyl alcohol, methanol), however, may be used. These mild solvents evaporate quickly and will not dissolve the polycarbonate.Other solutions that are not harmful are water-based lens cleaners or water-based detergents (with mild soap) formulated for cleaning CDs or DVDs.The polycarbonate substrate is a relatively soft and transparent type of plastic. Each time a disc is wiped, rubbed, treated with some solution, or otherwise manipulated for cleaning, that substrate, and thus the disc itself, is at risk of scratching or contamination.
If the disc needs cleaning, remember these tips:
• Use an air puffer to blow off dust.
• Use a soft cotton cloth or chamois to wipe the disc.
• Try cleaning with a dry cloth first, before using any cleaning solutions.
• Do not wipe in a direction going around the disc.
• Wipe from the center of the disc straight toward the outer edge.
• Avoid using paper products, including lens paper, to wipe the disc.
• Avoid using anything abrasive on the surface of the disc.
• If the disc has a heavy accumulation of dirt, try rinsing it with water
• Use commercially available water-based detergent formulated for cleaning the surface of optical discs.
• Use isopropyl alcohol or methanol, as an alternate to water-based detergents, to clean the disc surface.

Maintaining Your Discs


1. Handle discs by the outer edge or the center hole.
2. Use a non-solvent-based felt-tip permanent marker to mark the label side of the disc.
3. Keep dirt or other foreign matter from the disc.
4. Store discs upright (book style) in plastic cases specified for CDs and DVDs.
5. Return discs to storage cases immediately after use.
6. Leave discs in their packaging (or cases) to minimize the effects of environmental changes.
7. Open a recordable disc package only when you are ready to record data on that disc.
8. Store discs in a cool, dry, dark environment in which the air is clean.
9. Remove dirt, foreign material, fingerprints, smudges, and liquids by wiping with a clean cotton fabric in a straight line from the center of the disc toward the outer edge.
10. Use CD/DVD-cleaning detergent, isopropyl alcohol, or methanol to remove stubborn dirt or material.
11. Check the disc surface before recording.

Do not:

1. Touch the surface of the disc.
2. Bend the disc.
3. Use adhesive labels.
4. Store discs horizontally for a long time (years).
5. Open a recordable optical disc package if you are not ready to record.
6. Expose discs to extreme heat or high humidity.
7. Expose discs to extremely rapid temperature or humidity changes.
8. Expose recordable discs to prolonged sunlight or other sources of ultraviolet light.
9. Write or mark in the data area of the disc (the area the laser “reads”).
10. Clean by wiping in a direction going around the disc.

For CDs especially do not:

1. Scratch the label side of the disc.
2. Use a pen, pencil, or fine-tip marker to write on the disc.
3. Write on the disc with markers that contain solvents.
4. Try to peel off or reposition a label.

A brief note on CD-DVD technology

CDs and DVDs: Operation and Variety

CD is short for compact disc. DVD initially stood for digital video disc, then digital versatile disc, but today the term DVD is often used without referring to a specific set of words. Both CDs and DVDs are optical media, meaning media that use light technology (more specifically,laser light) for data retrieval. A disc drive focuses a laser light beam into the CD or DVD to “read” the bits (data) in the disc. The drive can also “write” bits by focusing the laser beam into recordable CDs or DVDs. The laser reads and writes data starting from the center of the disc and proceeding in a spiral direction toward the outer edge. A pre-groove is stamped in all blank recordable and rewritable CDs and DVDs to guide the laser as it writes.Optical discs are differentially identified to designate specific features such as recordability, rewritability, and accessibility. For example, CD-R, DVD-R, and DVD+R discs are dye-based recordable (write-once) discs—i.e., recordable but not erasable. CD-RW, DVD-RW, and DVD+RW discs are phase-change based, recordable, (rewritable) discs, or discs that permit the erasing of earlier information and the recording of new material in the same location on the disc. DVD-RAM discs are phase-change based, recordable (rewritable) discs formatted for random access,much like a computer hard drive. CD-ROM and DVD-ROM discs are pressed and molded,nonrecordable,read-only discs.


CDs and DVDs consist of the same basic materials and layers but are manufactured differently. A DVD is actually like two thin CDs glued together. A CD is read from and written to (by laser) on one side only; a DVD can be read from or written to on one or both sides, depending on how the disc was manufactured. Recordable DVDs (DVD-R, DVD-RW, DVD-RAM) can be manufactured with one recording
layer on each side. Prerecorded DVDs (DVD-ROM) can be manufactured with one or two recorded layers on each side.

Polycarbonate (Plastic) Substrate Layer

The polycarbonate substrate makes up most of the disc, including the area that is read by the laser (opposite the label side on CDs). It is present on both sides of a DVD, even a “single-sided” disc with a label on one side. This substrate provides the disc depth necessary to maintain laser focus on the metal and data layers. It also gives the disc enough strength to remain flat. Anything in or on the polycarbonate
layer that interferes with the ability of the laser to focus on the data layer will result in the misreading of data. Accordingly, fingerprints,smudges,or scratches,as well as such substances as dirt, dust, solvents, and excessive moisture (which polycarbonate will absorb), can interfere with the ability of the laser to read the data. Contact of any foreign material with the polycarbonate substrate layer should be avoided.

The dye-based (R discs) and the phase-changing film layers (RW discs) both hold data by allowing or blocking light transfer through the data layer.The laser-affected “written”) areas of the data layer absorb the “reading” laser beam as it is emitted from the laser to the metal layer and reflected back to the laser photosensor.The light and dark areas give reflectivity effects that are similar to the interference
effect of the “pressed” and molded data in the metal/substrate layer in ROM discs. The reflection, whether the result of dye, film, or pressed effects,is represented digitally as ones and zeros by the firmware in the disc drive as the laser reads the disc.

Data Layer in ROM Discs

ROM discs are commercially available or made-to-order prerecorded discs, also called “replicated” discs. Examples of CD-ROMs include the Audio-CD, Video-CD, CD-i, and CD+G, as well as any number of CDs used in computer applications. Among DVD-ROMs are the DVD-Video, DVD-Audio, and any of various DVDs used in games and computer applications.The data in CD-ROM or DVD-ROM discs are not actually in a separate layer. A molding machine uses a stamper to impress the pits (depressions) and lands (surface), which form the data, into the polycarbonate substrate surface. Metal is then sputtered or condensed onto the molded substrate to form a “reflective data layer.” The reflective metal layer in ROM discs can also be considered the data layer because the metal is integrated with the pits and lands in the polycarbonate.The metal layer in ROM discs is usually aluminum. For double-sided DVD-ROM discs, the semi-reflective layer is gold, silver alloy, or silicon.

Data Layer in R Discs

The recordable, write-once optical disc (CD-R, DVD-R, DVD+R) has its data-recording layer sandwiched between the polycarbonate strate and the metal layer. This layer is an organic dye. The dyes used in CDs and DVDs are the same basic types; those used in DVDs, however, are patented by the manufacturer, and the disc color does not indicate the type of dye used. The dyes in both CDs and DVDs are photosensitive. Bits (marks) are written to the dye by a chemical change caused by the laser light beam. This
dye degrades over time, eventually making the disc unreadable.The data layer in CD-R discs consists of one of three basic dye types, each yielding a different disc color depending on the type of dye and the type of reflective metal used in the disc. Even on a plain, unlabelled disc, the label side can be a different color from the reading side. If the label side of a recordable disc does not have a printable surface, a label attached, or some other protective layer, it will have the color of the metal used (silver or gold).

Data Layer in RW and RAM discs

The data-recording layer of the rewritable optical disc (CD-RW, DVD-RW, DVD+RW, DVD-RAM) also lies between the polycarbonDye ate substrate and the metal reflective layer. This is a phase-changing metal alloy film. A laser beam writes bits (marks) to the film by heating the film above the melting temperature in the areas selected for bits. The rapid cooling enabled by the dielectric layers on both sides of the phase-changing film causes these bit or mark areas to remain in the amorphous state caused by melting. By heating the phase-changing film to a specific temperature above the crystalline temperature but below the melting temperature, the film can revert back to the crystalline state, thereby erasing previous bits. The writing and erasing processes can be done together in a single pass when rewriting a disc.

Metal (Reflective) Layer

The metal layer in optical discs reflects the laser beam back to the laser
photosensor in the laser head. Three types of reflective metals are typically used for this layer: aluminum, gold, and silver or silver alloy.In “double-layer” DVDs, silicon is sometimes used as one of the semireflective layers.

Metal Layer in RW, ROM, and RAM Discs

RW, ROM, and RAM discs (CD-RW, CD-ROM, DVD-RW, DVD+RW, DVD-ROM, DVD-RAM) use aluminum for the reflective layer, mainly because it is inexpensive and easy to apply. Aluminum oxidizes on exposure to oxygen from the environment or to moisture that has penetrated the disc. In some earlier CDs, poor sealing allowed oxygen to come into contact with the aluminum metal layer, causing the aluminum to oxidize. Oxidation of the aluminum diminishes its reflectivity, making the disc unreadable by the laser, and is sometimes referred to as disc “rot.” It is the primary cause of ROM disc degradation from environmental influences. Not so, however, for RW and RAM disc degradation; the phase-changing film in these discs normally degrades at a faster rate than the aluminum in the disc oxidizes.

Metal Layer in R Discs

In R discs (CD-R, DVD-R, DVD+R), gold, silver, or a silver alloy is used for the reflective layer. Silver is slightly more reflective than gold but can lose reflectivity with corrosion on exposure to adverse environmental conditions. Silver corrodes through reaction with sulfur dioxide, an environmental pollutant that can migrate through the disc with moisture. Gold is noncorrosive, very stable, and longer lasting, but it is also expensive. Either metal should outlast the dye. Aluminum is not used with these discs because it can react with the dye in the recording (data) layer.

Metal Layers in Double-Layer DVD-ROM Discs

DVD-ROMs can be manufactured with two reflective metal layers that allow the laser to read data from both layers using one side of the disc. These “double layered” DVDs provide up to four times the capacity for content (video, audio, computer applications) as do “single-layered” DVDs. The laser beam must pass through a semi-reflective metal layer to read data from a fully reflective layer. The outer metal layer (silicon, gold, or silver alloy) is semi-reflective; that is, it reflects back some of the laser beam and allows some of it to pass through to a fully reflective layer (aluminum) and then reflect back. Both parts are thus reflected to, and detected by, the photosensor in the laser head, which focuses on one layer at a time.

These are a few points I had made note of from a few good ebooks.Not much detailed..but I couln't find more time to refine this..