DVD (Digital Versatile Disk) (page 5)
- Introduction
- DVD Formats
- DVD Configurations and Basic design
- DVD-R and DVD-RW or RAM
- DVD-ROM
- DVD-Video and DVD-Audio
- Red laser vs. Blue laser
- DVD-->VHS
- DVD-->DVD
- DVD R/RW Format Compatibility
- White Papers
DVD-R D-RW or RAM
There was a lot of confusion associated with the various recordable and rewritable DVD formats. The next table summarizes those competing formats and shows DVD-ROM for comparison.
| Format | DVD-ROM | DVD-R | DVD-RAM | DVD+RW | DVD-R/W | ASMO |
| Media | Pressed track (read only) | Dye-polymer (write once) | Phase change (rewritable) | Phase change (rewritable) | Phase change (rewritable) | Magneto-Optical (read / write) |
| Capacity, GB(for one side/one layer) | 4.7 | 3.95 | 2.6 | 3.0 | 3.95 | 6.0 |
| Track format | Land (no groove) | Groove | Land and groove (wobbled) | Groove (wobbled) | Groove (wobbled) | Land and groove |
| Supporters | DVD Forum | DVD Forum | Hitachi, Matsushita, Toshiba, and DVD Forum | Hewlett-Packard, Mitsubishi,Philips, Ricoh, Sony, Yamaha | Hitachi, Maxell, JVC,Mitsubishi, Pioneer, TDK | ASMO Group (Founders: Fujitsu,Hitachi, Imation, Olympus, Philips, Sanyo, Sharp, Sony) |
Recordable and rewritable DVD drives are clearly more complex than the DVD-ROM drives, since they require lasers with different power levels for reading, erasing, and writing. DVD-R media operates on a principle similar to the CD-R principle. The laser burns marks in a special dye layer and locally changes its reflectivity. Since the DVD-R uses a shorter-wavelength laser, it is incompatible with the green recordable media of CD-R, and another laser is required to solve this problem.
With the rewritable DVD, compatibility problems occur with the laser power-levels, since the drive needs different laser powers to record (cause phase transformation in the media), read ("measure" the reflectance), and erase (anneal the media) for both DVD and CD media. Some of today's DVD players can read all of the most important formats, such as DVD-RAM, DVD-ROM, DVD-Video, DVD-R, CD-Audio, CD-ROM, CD-R, CD-RW, and video CD but are, understandably, quite expensive.
The ASMO (for Advanced Storage Magneto-Optical Technology) disks are the same size as CDs and the ASMO drives are supposed to read CD-ROM and DVD disks. But, since they use magneto-optical principles instead of a phase-change process, the ASMO drives will not be able to record DVD-RAM disks.