Understanding the X, Compatibility Issues of CD-RW Drives, Media
Understanding the X, Compatibility Issues of CD-RW Drives, Media
CD-R's advantage and disadvantage is that the writing process is permanent. The media can't be erased or overwritten. This makes it ideal for archiving. Only by leaving a session "open" - that is, not recording on the entire CD -- can data be incrementally added to a disc. In so doing there is a risk of the disc not playing on all players. This obviously was not ideal for work-in-progress activities, very temporary projects or using the discs as a reusable backup solution.
On October 22, 1996, an industry consortium that now includes Ricoh, Philips, Sony, Yamaha, Hewlett-Packard, and Verbatim's parent company, Mitsubishi Chemical Corporation, announced CD-RW (CD-RW) to the world.
CD-RW was the next stop on the compact disc road map that started in 1980 with the introduction of compact disc digital audio by Philips and Sony.
The high-capacity, rewritable disc provided serious competition to the superfloppy alternatives that were being introduced and as history has proven the low-cost, single standard product quickly replaced the alternatives.
The CD-RW disc is based on Phase-Change technology, and can store 650-700 MB of computer data or 74-80 minutes of audio or video on a standard CD-size disc. There are no new formats associated with CD-RW; the existing CD formats such as CD-ROM, CD-Audio, PhotoCD, CD-I, etc. can all be used with CD-RW media. The CD-RW disc can be erased and re-written about 1,000 times (called cycleability), making it ideal for applications such as back-up and prototyping.
CD-RW is designed to be played back on most current CD-ROM drives as well as new DVD drives. With its multifunction capability, a CD-RW recorder can create CD-RW discs that are readable on the new DVD readers, as well as CD-R discs that are fully compatible with the current generation of CD-ROM drives and CD players.
Logo, Performance Specifications
To ensure consumers could play CD-RW media in every compliant recorder, player and drive, a new chapter was added to the Orange Book--Part III--that specifically addresses the CD-RW standard. This also incorporated a logical interchange standard -- Universal Disc Format (UDF) – was developed to provide a cohesive standard for packet writing. As part of the CD-RW Consortium’s efforts they also initiated a certification program called Multi-Read (MR). This helps CD-ROM drive and player manufacturers produce units that are fully CD-RW and UDF-compatible.
The Orange Book Part III or System Description CD-RW specifies the CD-RW disc format. The CD-RW system gives the opportunity to write, erase, overwrite and read CD information. The CD-RW disc has a lower reflectivity than a “Red Book or Yellow Book compatible” disc, so it must be played back on CD-RW enabled (MultiRead) CD players. A CD-RW enabled CD player can read CD-RW as well as CD-R and conventional CD discs.
As the industry continued to push the technology for higher performance drives and media, the Orange Book Part III specification and logo applications was reviewed and refined to ensure write and read compatibility as well as easy identification by the consumer. Today there are three volumes that precisely spell out the recorder/writer specifications that must be adhered to for optimum and continual write/read performance – Low Speed (1-4X), High Speed (4X – 12X) and Ultra Speed (12X – 24X).
Volume 1: Low Speed -- defines recording speed recorder/writer and media specifications of 1x, 2x and 4x nominal CD speed. (Latest version 2.0, Aug 1998). Because it was the initial specification for CD-RW there was no special logo identification applied to drives or media that met these specifications.
Volume 2: High Speed -- defines linear recording speed specifications between 4x and 12x nominal CD speed. (Latest version 1.1, June 2001). Drives and media produced to these specifications are identified with the High Speed CD-RW logo.
Volume 3: Ultra Speed -- defines linear recording speed specifications between 12x and 24x nominal CD speed. (Latest version 1.0, Sept 2002). Drives and media produced to these specifications are identified with the Ultra Speed CD-RW logo.
The User Challenge
When drive design and manufacturing moved from Low Speed to High Speed -- and soon to Ultra Speed --, a totally new set of control microprocessors and firmware had to be developed for the respective specification. At the same time, more advanced media manufacturing formulas and production techniques had to be developed specifically for these higher performance drives.
Because of the time constants of phase-change recording (explained later), new CD-RW media was developed to meet the write recording needs of the High Speed and Ultra Speed Orange Book Part III specifications. With each major write speed advance – High Speed and Ultra Speed – new subtype settings had to be defined to identify the discs. Some of the lower speed drives do not recognize these subtype settings and will therefore select their own default speed settings specific to their write strategies.
The result is unreadable signals which can result in overwriting or damaging previously recorded data. To prevent such problems, CD-RW Consortium members have developed additional Orange Book Part III protection for consumers which force write-incompatibility when High Speed or Ultra Speed CD-RW discs are used with lower performance drives.
When a few technically advanced drive manufacturers introduced High Speed CD-RW drives the units and media were “tuned” for optimum write reliability. The media was also fully backward compatible for in-specification Low Speed drives. Firms that chose to “stretch” the limits of their Low Speed drives delivered mixed writing performance for users.
Quality High Speed media would often perform properly on the first write pass on a High Speed drive that was merely a Low Speed drive pushed beyond Orange Book Part III specifications. Even if it did, the CD-RW media would quickly not perform properly in subsequent overwrites or edits.
That same situation is arising with some “Ultra Speed” drives. Firms that attempt to “extend” their High-Speed technologies into the Ultra Speed drive category deliver write/overwrite issues for consumers even when in-specification Ultra Speed CD-RW media is used in the drives.
In most instances, if the drive manufacturers upgrade the firmware of the current drives, the units will at least recognize the new higher speed discs. They will then write to the discs at their designed specification speed using modified write strategies.
As active members of the CD-RW Consortium, Mitsubishi Chemical and Verbatim adhere to the Orange Book Part III specifications in their development and manufacturing processes. Media is carefully produced and identified for its optimum performance rating – Low Speed, High Speed and Ultra Speed.
Phase-Change Technology
CD writers write data to the CD-R disc in a permanent manner. The laser burns the pits (actually bumps) into the organic dye layer of the CD-R disc by heating the spot to be recorded to about 300 - 400 degrees Celsius (temperature will depend on what speed the disc is recorded at). These recorded bumps have lower reflectivity than the surrounding lands, and are optically very close to the pits found in a stamped CD, having the same light scattering effects. Generally, the reflectivity of a CD-R disc is around 65%, meaning that 65% of the laser beam’s light is reflected back to the read head.
In contrast, a Phase-Change recording uses a higher-power laser to change the phase of the recording layer from its highly reflective ”crystalline” state to a lower reflective ”amorphous” state. This is accomplished by heating the spot to be recorded with a higher-power laser to about 600 degrees Celsius. As the spot cools, it becomes an amorphous ”mark” that is very close optically to the pit on a stamped CD. To change the spot back to the crystalline state, the laser uses a lower power setting and heats the amorphous mark to its glass transition temperature (about 200 degrees) and the spot will transform back to the crystalline state. The CD-RW approach is Direct Overwrite-compatible (DOW), which means that new data can be recorded directly over the old, eliminating the need to pre-erase.
Unfortunately, the Phase-Change disc has low reflectivity, around 25%. This is what prevents older CD drives from reading the Phase-Change CD-RW disc, the read heads in these drives cannot compensate for the lower reflectivity. The Red Book (the grandfather CD standard) specifies that discs will have 70% reflectivity. CD-R discs with 65% reflectivity are close enough optically that CD drives and CD players can read them with few exceptions. ”Multi-Read” (MR) drives have a simple circuit called Automatic Gain Control (AGC) that boosts the gain of the CD drive’s read head to compensate for the lower reflectivity of the CD-RW Phase-Change disc. DVD drives and players also have this AGC circuit.
The Phase-Change system employed in CD-RW is actually the reverse of other Phase-Change systems in use. Most other systems record a crystalline mark on an amorphous background (called burn bright) as opposed to CD-RW which records an amorphous mark on a crystalline background (burn dark). This is because the burn dark system is optically closer to the higher reflective lands and light scattering effects of pits on a stamped CD.
With CD-RW media, the laser is not only modulated off and on to form the correct size ”marks,” it is also modulated between write, erase and bias laser powers. Bias power is the same power used to read the disc and during recording it is modulated to keep the recording layer from absorbing too much heat, which would make distorted marks. The laser is modulated with the erase power because it is capable of directly overwriting old data. This process is called the Write Pulse Train (WPT). Based on the media inserted in the recorder, the firmware will set the correct Write Strategy.
The laser power for recording CD-RW discs is higher than it is for CD-ROMs. For example, a CD-R disc recorded at 48X needs a laser in the 8 – 10 milliwatt (mw) power range. For recording a CD-RW disc at 24X speed, a laser in the 8 – 14mw range is required. In the case of CD-R or CD-RW discs, the laser wavelength remains 780mn. 1n addition, the CD-RW recorders implement the AGC circuit to read back CD-RW compatible discs.
The OPC (Optimum Power Calibration) procedure for CD-RW discs is much like its CD-R cousins. The recommended recording laser power is encoded in the Absolute Time In Pre-groove (ATIP) of the disc and is read by the recorder’s firmware. The recorder then performs a test write of 6 sectors in the PCA (Power Calibration Area) of the CD-R disc with several different laser power values based on the recommended power, then reads the test sectors back and selects the laser power that produced the sector with the best reflectivity.
With CD-RW media, it is much the same, except in addition to the recommended write power being encoded in ATIP, the recommended erase power and bias powers are also encoded and read by the recorder. Running OPC, a technique developed for CD-R that can alter the laser power on the fly to compensate for media irregularities such as dust or fingerprints can also be applied to CD-RW media.
CD-RW Media Functionality
The only difference in the construction of a CD-RW disc and a CD-R disc is the recording layer (figure 1, 2). CD-R discs are constructed by injection molding the polycarbonate disc with its wobbled ”pre-groove.” Next, the organic dye is applied by spin-coating the dye onto the disc to ensure an even distribution of the dye. A gold reflective layer is then applied, followed by a protective coat of lacquer to protect the gold and dye. The printing on top of the lacquer layer is the last to be applied. When recording, the laser enters the polycarbonate disc and uses the wobbled pre-groove for tracking and rotation control. The recording takes place in the pre-groove on the dye layer.
With CD-RW discs, the disc starts out with the same polycarbonate base with the pre-groove, next comes the recording layer, which actually consists of four layers: the lower dielectric layer, the recording laser, the upper dielectric layer, and the reflective layer. The upper and lower dielectric layers draw away heat from the recording layer to keep heat from building up. Instead of organic dye, the recording layer is made up of a quaternary Phase-Change alloy consisting of silver, indium, antimony, and tellurium (Ag-In-Sb-Te). These elements make the Phase-Change recording possible. The reflective part of the recording layer is an aluminum alloy, just like in stamped discs. Gold was required by CD-R discs to get the reflectivity as high as possible and the organic dye tended to oxidize aluminum. After the recording layer, a layer of lacquer is applied to protect the recording layer ”sandwich”, and the printing is applied on top of the lacquer.
As with CD-R, the laser beam from the recorder enters the polycarbonate disc and uses the wobbled pre-groove for tracking and rotation control. The recording takes place in the pregroove, but the real action takes place in the alloy recording layer of the sandwich where the marks are recorded
Forward/Backward Compatibility
Multi-Read (MR) Program
The Multi-Read program was developed to bring CD-RW-compatible drives into the mass market. It is a self-certification that CD-ROM drive manufactures can use once they are compliant. In short, a MR-compatible CD-ROM drive will be able to:
* Read the lower reflective CD-RW discs
* Read a packet recorded disc
Because of the highly competitive nature of the CD drive market, most manufacturers support Multi-Read. The MR program has also been applied to DVD drives. This provides DVD drive buyers with the assurance that the drive can read all available CD media.
The MR program does not really apply to CD audio players, although it is logical that some high end CD player manufactures make their products compatible with the lower-reflective
CD-RW media. Music professionals will use for CD-RW media to back up sound files, but most will continue to make reference discs on CD-R discs playable at their client’s location.
Physical and Logical Standards
Physical Standards: The Color Books
CD-RW is fully compatible with the Red Book (CD Audio standard), Yellow Book (CD- ROM standard), Green Book (CD-I standard), White Book (Video CD Standard), Orange Book Part 1I (CD recordable standard) in every way except reflectivity. The CD-RW disc is the same physical size as the other discs, data is stored in the same formats, and is played in the same fashion. However, as previously explained, the reflectivity is lower for the CD-RW disc, about 25%. Orange Book Part III specifically addresses CD-RW technology. Orange Book Part III defines the lower reflective CD-RW disc, and how to record on it.
ISO 9660 Logical File System
ISO 9660 is the original file system developed for CD-ROM drives. It provides for cross- platform interchange of discs on PC, Macintosh, Linux and UNIX systems that were ISO 9660-compliant. One of the severe limitations of ISO 9660 is that the file system needs to know about all the files to be recorded in advance so the ”Path Tables” and ”Primary Volume Descriptor” (PVD) could be generated. These are the logical table of contents of what data is stored on the disc, and where it is located. Other limitations of ISO9660 included:
* File names must be only in capital letters, A – Z
* File names are limited to the DOS 8 + 3 format
* No more than 8 directory levels þ Only legal character besides letters is the under score ()
ISO 9660 was fine for creating discs with track-at-once or disc-at-once recording modes where pre-mastering software was used to select all the files in advance of recording, however, with the advent of packet writing, a more flexible file system was needed.
UDF 1.5 Logical File System
In 1995, the Optical Storage Technology Association (OSTA) began searching for a new logical file system that would be more flexible that ISO9660. As OSTA is an organization comprised of representatives from the major optical manufacturers, discussions led to the adoption of the Universal Disc Format (UDF). Essentially, UDF version 1.5 is very similar to ISO9660 in that it is capable of being cross platform. It does not, however, have the name and directory restrictions that ISO9660 imposed. With UDF, packet writing is handled in one of two ways:
* Track mode
* Random mode
In track mode UDF, a track on the CD-R/CD-RW disc is opened and the recording must take place sequentially in the track. There are areas in the track where temporary PVD and path tables are kept for updates to files. The track can be closed at any time and a session written around the packet track, using the temporary PVD and path table to build the PVD and path table for the session, or the track can stay in it’s native state. A device driver would be required to read the disc back on a standard CD-ROM drive today unless the session was closed in 1SO 9660 format. UDF track mode can be used with CD-R or CD-RW media.
In Random mode, the disc is ”formatted” into logical sectors, and these sectors are similar to those on a hard disk drive or optical drive. They can be randomly be written (and in the case of CD-RW media. randomly rewritten). Random mode UDF also provides for the defect management and can remap bad sectors so data isn’t stored in them. This is ideal for CD-RW as the cycleability is currently 1,000 overwrites. If a sector gets worn out, it can be mapped out and not used anymore, and a spare sector can be used. Random mode is clearly the most desirable way to use the disc, but has the most interchange problems, a device driver is definitely required to read this disc.
The good news is that UDF is supported by the various operating systems including MS Windows, Macintosh, Linux, etc. UDF allows packet writing to become a reality and interchangeable on CD-RW systems.
Understanding the X Compatibility Issues of CDRW Drives Media - To learn more about this author, visit Andy Marken's Website.
Like this article? Share it with your friends
Quick Review
CD-R's advantage and disadvantage is that the writing process is permanent. The media can't be erased or overwritten. This makes it ideal for archiving. Only by leaving a session "open" - that is, not recording on the entire CD -- can data be incrementally added to a disc. In so doing there is a risk of the disc not playing on all players. This obviously was not ideal for work-in-progress activities, very temporary projects or using the discs as a reusable backup solution.
On October 22, 1996, an industry consortium that now includes Ricoh, Philips, Sony, Yamaha, Hewlett-Packard, and Verbatim's parent company, Mitsubishi Chemical Corporation, announced CD-RW (CD-RW) to the world.
CD-RW was the next stop on the compact disc road map that started in 1980 with the introduction of compact disc digital audio by Philips and Sony.
The high-capacity, rewritable disc provided serious competition to the superfloppy alternatives that were being introduced and as history has proven the low-cost, single standard product quickly replaced the alternatives.
The CD-RW disc is based on Phase-Change technology, and can store 650-700 MB of computer data or 74-80 minutes of audio or video on a standard CD-size disc. There are no new formats associated with CD-RW; the existing CD formats such as CD-ROM, CD-Audio, PhotoCD, CD-I, etc. can all be used with CD-RW media. The CD-RW disc can be erased and re-written about 1,000 times (called cycleability), making it ideal for applications such as back-up and prototyping.
CD-RW is designed to be played back on most current CD-ROM drives as well as new DVD drives. With its multifunction capability, a CD-RW recorder can create CD-RW discs that are readable on the new DVD readers, as well as CD-R discs that are fully compatible with the current generation of CD-ROM drives and CD players.
Logo, Performance Specifications
To ensure consumers could play CD-RW media in every compliant recorder, player and drive, a new chapter was added to the Orange Book--Part III--that specifically addresses the CD-RW standard. This also incorporated a logical interchange standard -- Universal Disc Format (UDF) – was developed to provide a cohesive standard for packet writing. As part of the CD-RW Consortium’s efforts they also initiated a certification program called Multi-Read (MR). This helps CD-ROM drive and player manufacturers produce units that are fully CD-RW and UDF-compatible.
The Orange Book Part III or System Description CD-RW specifies the CD-RW disc format. The CD-RW system gives the opportunity to write, erase, overwrite and read CD information. The CD-RW disc has a lower reflectivity than a “Red Book or Yellow Book compatible” disc, so it must be played back on CD-RW enabled (MultiRead) CD players. A CD-RW enabled CD player can read CD-RW as well as CD-R and conventional CD discs.
As the industry continued to push the technology for higher performance drives and media, the Orange Book Part III specification and logo applications was reviewed and refined to ensure write and read compatibility as well as easy identification by the consumer. Today there are three volumes that precisely spell out the recorder/writer specifications that must be adhered to for optimum and continual write/read performance – Low Speed (1-4X), High Speed (4X – 12X) and Ultra Speed (12X – 24X).
Volume 1: Low Speed -- defines recording speed recorder/writer and media specifications of 1x, 2x and 4x nominal CD speed. (Latest version 2.0, Aug 1998). Because it was the initial specification for CD-RW there was no special logo identification applied to drives or media that met these specifications.
Volume 2: High Speed -- defines linear recording speed specifications between 4x and 12x nominal CD speed. (Latest version 1.1, June 2001). Drives and media produced to these specifications are identified with the High Speed CD-RW logo.
Volume 3: Ultra Speed -- defines linear recording speed specifications between 12x and 24x nominal CD speed. (Latest version 1.0, Sept 2002). Drives and media produced to these specifications are identified with the Ultra Speed CD-RW logo.
The User Challenge
When drive design and manufacturing moved from Low Speed to High Speed -- and soon to Ultra Speed --, a totally new set of control microprocessors and firmware had to be developed for the respective specification. At the same time, more advanced media manufacturing formulas and production techniques had to be developed specifically for these higher performance drives.
Because of the time constants of phase-change recording (explained later), new CD-RW media was developed to meet the write recording needs of the High Speed and Ultra Speed Orange Book Part III specifications. With each major write speed advance – High Speed and Ultra Speed – new subtype settings had to be defined to identify the discs. Some of the lower speed drives do not recognize these subtype settings and will therefore select their own default speed settings specific to their write strategies.
The result is unreadable signals which can result in overwriting or damaging previously recorded data. To prevent such problems, CD-RW Consortium members have developed additional Orange Book Part III protection for consumers which force write-incompatibility when High Speed or Ultra Speed CD-RW discs are used with lower performance drives.
When a few technically advanced drive manufacturers introduced High Speed CD-RW drives the units and media were “tuned” for optimum write reliability. The media was also fully backward compatible for in-specification Low Speed drives. Firms that chose to “stretch” the limits of their Low Speed drives delivered mixed writing performance for users.
Quality High Speed media would often perform properly on the first write pass on a High Speed drive that was merely a Low Speed drive pushed beyond Orange Book Part III specifications. Even if it did, the CD-RW media would quickly not perform properly in subsequent overwrites or edits.
That same situation is arising with some “Ultra Speed” drives. Firms that attempt to “extend” their High-Speed technologies into the Ultra Speed drive category deliver write/overwrite issues for consumers even when in-specification Ultra Speed CD-RW media is used in the drives.
In most instances, if the drive manufacturers upgrade the firmware of the current drives, the units will at least recognize the new higher speed discs. They will then write to the discs at their designed specification speed using modified write strategies.
As active members of the CD-RW Consortium, Mitsubishi Chemical and Verbatim adhere to the Orange Book Part III specifications in their development and manufacturing processes. Media is carefully produced and identified for its optimum performance rating – Low Speed, High Speed and Ultra Speed.
Phase-Change Technology
CD writers write data to the CD-R disc in a permanent manner. The laser burns the pits (actually bumps) into the organic dye layer of the CD-R disc by heating the spot to be recorded to about 300 - 400 degrees Celsius (temperature will depend on what speed the disc is recorded at). These recorded bumps have lower reflectivity than the surrounding lands, and are optically very close to the pits found in a stamped CD, having the same light scattering effects. Generally, the reflectivity of a CD-R disc is around 65%, meaning that 65% of the laser beam’s light is reflected back to the read head.
In contrast, a Phase-Change recording uses a higher-power laser to change the phase of the recording layer from its highly reflective ”crystalline” state to a lower reflective ”amorphous” state. This is accomplished by heating the spot to be recorded with a higher-power laser to about 600 degrees Celsius. As the spot cools, it becomes an amorphous ”mark” that is very close optically to the pit on a stamped CD. To change the spot back to the crystalline state, the laser uses a lower power setting and heats the amorphous mark to its glass transition temperature (about 200 degrees) and the spot will transform back to the crystalline state. The CD-RW approach is Direct Overwrite-compatible (DOW), which means that new data can be recorded directly over the old, eliminating the need to pre-erase.
Unfortunately, the Phase-Change disc has low reflectivity, around 25%. This is what prevents older CD drives from reading the Phase-Change CD-RW disc, the read heads in these drives cannot compensate for the lower reflectivity. The Red Book (the grandfather CD standard) specifies that discs will have 70% reflectivity. CD-R discs with 65% reflectivity are close enough optically that CD drives and CD players can read them with few exceptions. ”Multi-Read” (MR) drives have a simple circuit called Automatic Gain Control (AGC) that boosts the gain of the CD drive’s read head to compensate for the lower reflectivity of the CD-RW Phase-Change disc. DVD drives and players also have this AGC circuit.
The Phase-Change system employed in CD-RW is actually the reverse of other Phase-Change systems in use. Most other systems record a crystalline mark on an amorphous background (called burn bright) as opposed to CD-RW which records an amorphous mark on a crystalline background (burn dark). This is because the burn dark system is optically closer to the higher reflective lands and light scattering effects of pits on a stamped CD.
With CD-RW media, the laser is not only modulated off and on to form the correct size ”marks,” it is also modulated between write, erase and bias laser powers. Bias power is the same power used to read the disc and during recording it is modulated to keep the recording layer from absorbing too much heat, which would make distorted marks. The laser is modulated with the erase power because it is capable of directly overwriting old data. This process is called the Write Pulse Train (WPT). Based on the media inserted in the recorder, the firmware will set the correct Write Strategy.
The laser power for recording CD-RW discs is higher than it is for CD-ROMs. For example, a CD-R disc recorded at 48X needs a laser in the 8 – 10 milliwatt (mw) power range. For recording a CD-RW disc at 24X speed, a laser in the 8 – 14mw range is required. In the case of CD-R or CD-RW discs, the laser wavelength remains 780mn. 1n addition, the CD-RW recorders implement the AGC circuit to read back CD-RW compatible discs.
The OPC (Optimum Power Calibration) procedure for CD-RW discs is much like its CD-R cousins. The recommended recording laser power is encoded in the Absolute Time In Pre-groove (ATIP) of the disc and is read by the recorder’s firmware. The recorder then performs a test write of 6 sectors in the PCA (Power Calibration Area) of the CD-R disc with several different laser power values based on the recommended power, then reads the test sectors back and selects the laser power that produced the sector with the best reflectivity.
With CD-RW media, it is much the same, except in addition to the recommended write power being encoded in ATIP, the recommended erase power and bias powers are also encoded and read by the recorder. Running OPC, a technique developed for CD-R that can alter the laser power on the fly to compensate for media irregularities such as dust or fingerprints can also be applied to CD-RW media.
CD-RW Media Functionality
The only difference in the construction of a CD-RW disc and a CD-R disc is the recording layer (figure 1, 2). CD-R discs are constructed by injection molding the polycarbonate disc with its wobbled ”pre-groove.” Next, the organic dye is applied by spin-coating the dye onto the disc to ensure an even distribution of the dye. A gold reflective layer is then applied, followed by a protective coat of lacquer to protect the gold and dye. The printing on top of the lacquer layer is the last to be applied. When recording, the laser enters the polycarbonate disc and uses the wobbled pre-groove for tracking and rotation control. The recording takes place in the pre-groove on the dye layer.
With CD-RW discs, the disc starts out with the same polycarbonate base with the pre-groove, next comes the recording layer, which actually consists of four layers: the lower dielectric layer, the recording laser, the upper dielectric layer, and the reflective layer. The upper and lower dielectric layers draw away heat from the recording layer to keep heat from building up. Instead of organic dye, the recording layer is made up of a quaternary Phase-Change alloy consisting of silver, indium, antimony, and tellurium (Ag-In-Sb-Te). These elements make the Phase-Change recording possible. The reflective part of the recording layer is an aluminum alloy, just like in stamped discs. Gold was required by CD-R discs to get the reflectivity as high as possible and the organic dye tended to oxidize aluminum. After the recording layer, a layer of lacquer is applied to protect the recording layer ”sandwich”, and the printing is applied on top of the lacquer.
As with CD-R, the laser beam from the recorder enters the polycarbonate disc and uses the wobbled pre-groove for tracking and rotation control. The recording takes place in the pregroove, but the real action takes place in the alloy recording layer of the sandwich where the marks are recorded
Forward/Backward Compatibility
Multi-Read (MR) Program
The Multi-Read program was developed to bring CD-RW-compatible drives into the mass market. It is a self-certification that CD-ROM drive manufactures can use once they are compliant. In short, a MR-compatible CD-ROM drive will be able to:
* Read the lower reflective CD-RW discs
* Read a packet recorded disc
Because of the highly competitive nature of the CD drive market, most manufacturers support Multi-Read. The MR program has also been applied to DVD drives. This provides DVD drive buyers with the assurance that the drive can read all available CD media.
The MR program does not really apply to CD audio players, although it is logical that some high end CD player manufactures make their products compatible with the lower-reflective
CD-RW media. Music professionals will use for CD-RW media to back up sound files, but most will continue to make reference discs on CD-R discs playable at their client’s location.
Physical and Logical Standards
Physical Standards: The Color Books
CD-RW is fully compatible with the Red Book (CD Audio standard), Yellow Book (CD- ROM standard), Green Book (CD-I standard), White Book (Video CD Standard), Orange Book Part 1I (CD recordable standard) in every way except reflectivity. The CD-RW disc is the same physical size as the other discs, data is stored in the same formats, and is played in the same fashion. However, as previously explained, the reflectivity is lower for the CD-RW disc, about 25%. Orange Book Part III specifically addresses CD-RW technology. Orange Book Part III defines the lower reflective CD-RW disc, and how to record on it.
ISO 9660 Logical File System
ISO 9660 is the original file system developed for CD-ROM drives. It provides for cross- platform interchange of discs on PC, Macintosh, Linux and UNIX systems that were ISO 9660-compliant. One of the severe limitations of ISO 9660 is that the file system needs to know about all the files to be recorded in advance so the ”Path Tables” and ”Primary Volume Descriptor” (PVD) could be generated. These are the logical table of contents of what data is stored on the disc, and where it is located. Other limitations of ISO9660 included:
* File names must be only in capital letters, A – Z
* File names are limited to the DOS 8 + 3 format
* No more than 8 directory levels þ Only legal character besides letters is the under score ()
ISO 9660 was fine for creating discs with track-at-once or disc-at-once recording modes where pre-mastering software was used to select all the files in advance of recording, however, with the advent of packet writing, a more flexible file system was needed.
UDF 1.5 Logical File System
In 1995, the Optical Storage Technology Association (OSTA) began searching for a new logical file system that would be more flexible that ISO9660. As OSTA is an organization comprised of representatives from the major optical manufacturers, discussions led to the adoption of the Universal Disc Format (UDF). Essentially, UDF version 1.5 is very similar to ISO9660 in that it is capable of being cross platform. It does not, however, have the name and directory restrictions that ISO9660 imposed. With UDF, packet writing is handled in one of two ways:
* Track mode
* Random mode
In track mode UDF, a track on the CD-R/CD-RW disc is opened and the recording must take place sequentially in the track. There are areas in the track where temporary PVD and path tables are kept for updates to files. The track can be closed at any time and a session written around the packet track, using the temporary PVD and path table to build the PVD and path table for the session, or the track can stay in it’s native state. A device driver would be required to read the disc back on a standard CD-ROM drive today unless the session was closed in 1SO 9660 format. UDF track mode can be used with CD-R or CD-RW media.
In Random mode, the disc is ”formatted” into logical sectors, and these sectors are similar to those on a hard disk drive or optical drive. They can be randomly be written (and in the case of CD-RW media. randomly rewritten). Random mode UDF also provides for the defect management and can remap bad sectors so data isn’t stored in them. This is ideal for CD-RW as the cycleability is currently 1,000 overwrites. If a sector gets worn out, it can be mapped out and not used anymore, and a spare sector can be used. Random mode is clearly the most desirable way to use the disc, but has the most interchange problems, a device driver is definitely required to read this disc.
The good news is that UDF is supported by the various operating systems including MS Windows, Macintosh, Linux, etc. UDF allows packet writing to become a reality and interchangeable on CD-RW systems.
Understanding the X Compatibility Issues of CDRW Drives Media - To learn more about this author, visit Andy Marken's Website.
Like this article? Share it with your friends
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Dave KurlanDave Kurlan is the founder and CEO of Objective Management Group, Inc., the industry leader in sales assessments and sales force evaluations, and the CEO of David Kurlan & Associates, Inc., a consulting firm specializing in sales force development. Dave has been a top rated speaker at Inc. Magazine's Conference on Growing the Company, the Sales & Marketing Management Conference and the Gazelles Sales & Marketing Summit. He has been featured on radio and TV, including World Business Review with General Norman Schwarzkopf, in Inc. Magazine, Selling Power Magazine, Sales & Marketing Management Magazine and Incentive Magazine. He is the author of Mindless Selling and Baseline Selling – How to Become a Sales Superstar by Using What You Already Know about the Game of Baseball. He created and wrote STAR, a proprietary recruiting process for hiring great salespeople, and he writes Understanding the Sales Force, a popular business Blog and is a contributing author to The Death of 20th Century Selling and 101 Great Ways to Improve Your Life, Volume 2. - Visit Dave Kurlan's Website |
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Joe DagerJoe Dager is President of Business901, a progressive coaching company providing no-nonsense direction in areas such as Lean Six Sigma Marketing and organized referral marketing. What others say: In the past 20 years, Joe and I have collaborated on many difficult issues. Joe’s ability to combine his expertise with “out of the box” thinking is unsurpassed. He has always delivered quickly, cost effectively and with ingenuity. A brilliant mind that is always a pleasure to work with.” - James R. If you want to learn more about Business901, start a conversation with us. We can be found @ Web/Blog: Business901.com Web/Blog: FundingYourNonprofit.com LinkedIn Profile Follow me on Twitter - Visit Joe Dager's Website |
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Stephanie RobeyStephanie Robey is President and CoFounder of Pivot Positive, LLC - an Internet marketing business focused on helping people start work at home ventures. Previously, she was employed at The Search Agency with over 20 years experience in graphic design and 10 years experience in online marketing. She was responsible for launching the Conversion Path Optimization (CPO) unit where she and her team have conducted hundreds of optimization tests for online companies across multiple verticals. She is a successful entrepreneur having started and sold 2 companies and remains on the board of directors of the third, PhotoSpin.com Stephanie began her career in the direct marketing realm creating and producing direct mail for many of the major cable television companies and directly attributes her understanding of Internet marketing to those early offline experiences. Stephanie is a graduate of San Diego State University with a BFA in Graphic Arts and also holds an Executive MBA from the Graziadio School of Business and Management at Pepperdine University. Read Steph's Blog Meet Steph and Dave Sign up for our Free 7-Day BootCamp: Self Employed & Rich - Visit Stephanie Robey's Website |
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