Copyright OSTA 2004
All rights reserved.


Understanding DVD

Author's Notes
Physical Logical and

Recording Hardware
Recording Speed
>Physical Compatibility
Disc Size Configuration and Capacity
Copying Deterrents and Content Protection
Duplication, Replication and Publishing
Disc Labeling
Disc Handling, Storage
and Disposal

Disc Longevity
Disc Testing and

Disc Construction and

Appendix A - Further
Reading and Resources

Appendix B - Industry
and Product Contacts
About OSTA
About the Author







What types of devices read DVD-R and DVD+R discs?
Once written, single-layer (SL) DVD-R and DVD+R discs closely mimic the optical characteristics of single-layer (SL) prerecorded (pressed) DVDs. Thus, they can be read on the majority of computer DVD-ROM drives and DVD recorders. In addition, DVD-R and DVD+R discs are compatible with most consumer electronics (CE) DVD devices including portable, car and DVD players and recorders. Compatibility continues to evolve so newer devices are generally more able to play written discs. For example, some early DVD video players were released before the DVD-R specifications were completed so they do not recognize DVD-R discs. Some manufacturers suggest that under certain circumstances DVD+R can work around this issue by having the recorder write the disc using the prerecorded disc identification code thereby allowing the player to treat it as a pressed disc (see “DVD disc category” below). If in doubt, consult with the hardware manufacturer.

What types of devices read DVD-RW and DVD+RW discs?
Written DVD-RW and DVD+RW discs can be read on the majority of computer DVD-ROM drives and DVD recorders as well as consumer electronics (CE) DVD devices including portable, car and DVD players and recorders. However, DVD-RW and DVD+RW discs have optical signal characteristics (lower reflectivity) closer to those of dual-layer (DL) prerecorded (pressed) DVDs which sometimes contributes to incompatibilities (see “DVD disc category” below). As with DVD-R and DVD+R, compatibility continues to evolve so some devices (typically older) may not be able to play written discs. If in doubt, consult with the hardware manufacturer.

What types of devices read DVD-RAM discs?
DVD-RAM discs are significantly different from prerecorded DVDs (data in land and groove areas, embossed sector headers, lower reflectivity and signal modulation, hardware-based defect management, optional cartridge, etc.). As a result, only devices specifically designed to be DVD-RAM compatible can read DVD-RAM discs. These include DVD Multi-compliant computer and consumer electronics (CE) drives, players and recorders as well as other DVD-RAM recorders and DVD-ROM drives expressly supporting DVD-RAM. Keep in mind that not all devices accommodate cartridged discs. As well, there have been several generations of DVD-RAM technology so previous and current versions of discs and devices may not be compatible with one other. Specifically, early DVD-RAM recorders and DVD-RAM compatible DVD-ROM drives read only 2.6 GB single-sided (SS) and 5.2 GB double-sided (DS) discs. In addition, DVD Multi-compliant and DVD-RAM consumer electronics (CE) recorders and players cannot read 2.6 GB (SS) and 5.2 GB (DS) discs. If in doubt, consult with the hardware manufacturer.

What is DVD Multi?
The DVD Forum created the DVD Multi specification in 2001 to provide hardware manufacturers with the requirements necessary to make computer and consumer electronics (CE) DVD devices read or read and write most DVD disc formats sanctioned by the DVD Forum. Specifically, the DVD Multi specification requires that DVD Multi Players read DVD-ROM (prerecorded), DVD-R (General), DVD-RW and DVD-RAM discs and DVD Multi Recorders read and write those same formats. Be aware that DVD Multi does not prescribe that devices should accommodate DVD-RAM cartridges or 8 cm discs. If in doubt, consult with the hardware manufacturer.

Examples of Discs Readable and Writable by
DVD Multi Compliant Drives, Players and Recorders

Type of Disc
DVD Multi Player
DVD Multi Recorder
DVD-ROM (prerecorded)
DVD-R (General)

* DVD Multi consumer electronics (CE) devices are not compatible with 2.6/5.2GB DVD-RAM discs.

What isthe "DVD disc category" and how can it affect playback compatibility?
Contained within the Lead-In Area of a DVD disc is information about its physical format including its “disc category” (also known as “book type”). This refers to the kind of disc it is as defined by one of the many DVD Forum specifications or “books”. Currently, there are four categories — prerecorded (pressed) DVD, DVD-RAM, DVD-R and DVD-RW. DVD Forum specifications do not govern DVD+R and DVD+RW therefore these discs use other categories.

Playback problems can arise (typically in some older devices) if the playing unit is programmed to ignore the category information or to accept only prerecorded discs or the four DVD Forum defined types. To potentially improve the playback compatibility of DVD+R and DVD+RW discs in such devices some DVD recorders are designed to write, or optionally write, these discs with the prerecorded (pressed) category code. Since DVD+RW discs are rewritable various routines (for consumer electronics recorders) or software (for computer recorders) are sometimes made available that can rewrite the disc category code in both its native DVD+RW and the prerecorded setting. Not all DVD+R/+RW compatible recorders support making these changes and, in general, manufacturers advise against changing a disc’s category setting unless this specific playback problem is encountered and others recommend against this practice entirely.

DVD Disc Categories

Disc Format
Disc Category
Disc Specification Source
Prerecorded (pressed) DVD
DVD Forum
DVD Forum
DVD Forum
DVD Forum
DVD+RW Alliance
DVD+RW Alliance