There are five recordable versions of DVD:
- DVD-R for General
- DVD-R for Authoring
- DVD-RW, and
All writable DVD formats include a set of specifications that define a media’s physical traits and characteristics. This layer of functionality is the media’s physical layer, and a particular player or drive’s ability to play a disc depends on its ability to support its associated physical layer, regardless of what type of data is stored on it. The specification of the content itself is subject to a number of application layers, defined by the DVD Forum. Motion pictures are typically released on replicated ROM media (the physical layer) and authored using the DVD-Video format (the application layer).
The DVD-Video format is essentially a publishing format, intended for use in a one-time-only mastering process. However, DVD video recorders can also use another application layer, known as the Video Recording (VR) format. The VR format was created by the DVD Forum in order to offer functionality that is very similar to that of videotape recorders (VCRs). For example, consider the very common VCR function of randomly inserting a video segment anywhere on a tape. Attempting this on disc using a DVD Video application layer would likely be difficult and time-consuming, since the recorder would have to track and repair any unexpected changes in the navigational functions of the disc. The VR format was designed to make such functions simple, allowing tape-like flexibility whilst at the same time providing new features such as automatic location of blank areas and a visual table of contents of recordings on the disc.
All recordable drives can read DVD-ROM discs, but each uses a different type of disc for recording. DVD-R – which first became available in 1997, can record data once (sequentially only), while the rewritable formats – DVD-RAM, DVD-RW and DVD+RW – can all be rewritten thousands of times.
DVD-RAM was the first rewritable format to come to market, first appearing in the summer of 1998. It is the best suited of the writable DVD formats for use in computers, because of its defect management and zoned CLV format for rapid access. It is not compatible with most drives and players (because of defect management, reflectivity differences, and minor format differences).
The DVD-RW and DVD+RW formats are similar in that both represent a more evolutionary development of existing CD-RW/DVD-R technology – and to therefore provide better compatibility with the rest of the CD/DVD family of products. DVD-RW was first available in Japan in late 1999, but not elsewhere until 2001. DVD+RW has suffered a number of false starts and is not now expected to appear before late-2001.
Despite having a head start of nearly three years on its rivals, DVD-RAM has failed to achieve a critical mass in that time, and it is by no means certain that it will emerge as the winner in the battle of the rewritable formats. Assuming that DVD+RW drives match DVD-RW drives’ capability to write to DVD-R(G) and CD-R/RW media, DVD-RAM are likely to be significantly less versatile than both of its rivals. The DVD-RW and DVD+RW formats have so much in common that it is difficult to see how both can become successfully established. Perhaps the answer lies in market positioning. On the one hand, DVD-RW is criticised for its lack of either a defect management system or support for variable bit rate video recording. On the other, as of mid-2001 consumers were still waiting for the much-delayed DVD+RW format to reach the marketplace.
- History of DVD development and birth of the DVD Forum
- DVD Formats
- DVDs – digital versatile disks – how they’re made and how they work
- DVD OSTA
- DVD File Systems
- CDR-RW Compatibility Issues
- DVD Encoding
- DVD Content Protection
- Regional codes for DVDs
- DVD DivX Codec
- DVD Recordable Formats
- DVD-R – write once recordable DVDs
- DVD Multi-Writers