DVD-RAM and DVD-RW are re-writable disc formats both with a capacity of 4.7GB per side. DVD-RAM and DVD-RW are the two official re-writable DVD formats. Both formats use phase change recording where the active layer is made to change between amorphous and crystalline state by means of a laser at different power. The differences between the two formats are shown in the table below.
| Parameter | DVD-RAM Ver 1.0 |
DVD-RAM Ver 2.0 |
DVD-RW Ver 1.0 |
| Sides | 1 or 2 | 1 or 2 | 1 or 2 |
| Capacity (GB) | 2.6 per side | 4.7 per side | 4.7 per side |
| Recording method | Phase change marks | ||
| Track format | Wobbled Land & Groove | Wobble groove | |
| Track pitch (microns) | 0.74 | 0.615 | 0.74 |
| Min pit length (microns) | 0.41 | 0.28 | 0.40 |
| Number of zones | 24 | 35 | |
| User data rate (Mb/s) | 11.08 | 22.16 | |
| Caddy | Yes | ||
| Modulation and error correction | 8 to 16 & RSPC | ||
DVD-RAM
DVD-RAM discs use land/groove recording and Zoned CLV (ZCLV) method instead of CLV, where the angular velocity continuously changes. Within each zone the
data is written/read using the CAV method, the angular velocity changing from zone to zone to maintain a constant average linear velocity. The data is
written on both land and groove, the address information being molded into the disc as pits.
The current specification (version 2.1) is for 4.7GB or 9.4GB (double sided) capacity media (12 cm) which offer over 100,000 recording cycles and a 30-year life or more.
Copy protection has been added with CPRM.
DVD-RW
DVD-RW discs use groove recording offering a 4.7GB capacity per side and does not need a cartridge. It offers advantages over tape in life (videotape life
is only 15 to 20 years) and the ability to edit home movies. DVD-RW discs are designed to be compatible with existing players and drives. Discs are
recordable over 1,000 times and they have the same optical properties as a DVD-9 disc.
DVD-RW discs can be used for videotape replacement, video authoring and desktop PC backup. Consumer applications include video recording and home authoring. DVD-RW discs also offer CPRM copy protection and can include BCA serialization.
DVD+RW
Another re-writable format, DVD+RW, was developed and proposed by Hewlett-Packard, Philips, and Sony with the support of Verbatim, Ricoh and Yamaha.
Philips and Sony are also members of the DVD Forum but believe that DVD+RW is more compatible with existing DVD-ROM drives than DVD-RAM. DVD+RW discs have
a capacity of 4,7GB and do not need a cartridge.
Features of DVD+RW are claimed to be:
- Compatible with DVD-ROM drives
- No need for cartridge/caddy
- 4.7GB capacity
- Choice of CAV for high performance data storage applications and CLV for video recording
- Backed by industry leaders in CD-RW
DVD+RW is now available but is not supported by the DVD Forum.
