PHYSICAL COMPATIBILITY

What types of devices read CD-R discs?
Once written, CD-R discs closely mimic the optical characteristics of prerecorded (pressed) CDs. As a result, they can be read on almost any computer CD-ROM drive, CD-R or CD-R/RW recorder or MultiRead-compliant DVD-ROM drive or recorder. Additionally, CD-R discs are compatible with most consumer electronics devices including portable, car and set-top CD audio players and MultiPlay-compliant DVD-Video players and recorders. All DVD devices that read CD-R discs do not necessarily display the MultiRead or MultiPlay logos. If in doubt, consult with the hardware manufacturer.

What types of devices read CD-RW discs?
Written CD-RW discs have slightly different optical characteristics (lower reflectivity and signal modulation) than prerecorded (pressed) and written CD-R discs and therefore are not as widely compatible. They can be read only on MultiRead-compliant CD-ROM drives, CD-R/RW recorders and MultiRead-compliant DVD-ROM drives and recorders. CD-RW discs are, in addition, compatible with some consumer electronics devices including MultiPlay-compliant portable, car and set-top CD audio players and MultiPlay-compliant DVD-Video players and recorders. Again, all CD and DVD devices that read CD-RW discs do not necessarily display the MultiRead or MultiPlay logos. If in doubt, consult with the hardware manufacturer.

What is MultiRead?
The MultiRead specification was created by OSTA in 1997 to provide hardware manufacturers with the requirements necessary to make CD-ROM drives and recorders read CD-RW discs. MultiRead also bridges the differences between CD and DVD technologies and provides the framework for DVD-ROM drives and recorders to read CD-R and CD-RW discs. Specifically, MultiRead requires that compatible drives read Red Book CD audio and CD-ROM information contained on prerecorded (pressed), CD-R and CD-RW discs.

Examples of Discs Readable by
MultiRead-Compliant Drives and Recorders

What is MultiPlay?
The MultiPlay specification was created by OSTA in 2000 to provide hardware manufacturers with the requirements necessary to make CD and DVD consumer electronics devices play CD-R and CD-RW discs. Specifically, MultiPlay requires that all compatible devices play prerecorded (pressed), CD-R and CD-RW discs in Red Book audio format. As well, devices with CD-Text and VideoCD capabilities must also play these formats when written on CD-R and CD-RW discs.

Why can’t all DVD devices read CD-R and CD-RW discs?
DVD format specifications deal with elements of disc design and not the hardware that reads them. As a result, DVD device manufacturers are free to incorporate whatever features they like into their products, including deciding which types of discs are supported. Consumer demand and cost considerations are taken into account by manufacturers who then construct their products and marketing accordingly.

In addition to these market forces a number of technical issues come into play. Despite appearances to the contrary, a CD and a DVD are distinctively different physically from each other. For example, a DVD disc uses a substrate half as thick as does a CD (0.6 mm vs. 1.2 mm) as well as smaller pit and lands and has less distance between the coils of the data track. A DVD is also read using a shorter wavelength laser (650 nm red vs. 780 nm infra-red) through an optical lens with a larger numerical aperture (0.60 vs. 0.45). Thus, DVD devices which also read prerecorded (pressed) CDs employ a number of tactics to accommodate these differences. However, a CD-R disc has its own unique construction so reading it requires additional hardware components.

Unlike the molded plastic pits of a prerecorded disc the optical responses of the organic dyes used in the recording layer of a CD-R disc are carefully designed to function in the 780 nm range used by CD drives and recorders. Consequently, when a CD-R disc is read using the shorter 650 nm DVD laser wavelength the signals returned from the disc are greatly diminished and may not be read reliably. DVD devices that are designed to read DVD and CD-R discs (such as those compliant with MultiRead and MultiPlay specifications) compensate for this problem by incorporating dual laser optical pickups to generate both 650 nm and 780 nm wavelengths.

A CD-RW disc is a little different. The optical response of the phase change material used in its recording layer is not as wavelength dependent as organic dye in a CD-R and can be read using a 650 nm laser. However, because a CD-RW disc has relatively low reflectivity and signal modulation the optical systems of some DVD devices may not be sensitive enough to read it.

CONTINUE TO DISC SIZE AND CAPACITY