DVD-RAM (DVD–Random Access Memory) is a disc specification presented in 1996 by the DVD Forum, which specifies rewritable DVD-RAM media and the appropriate DVD writers. DVD-RAM media have been used in computers as well as camcorders and personal video recorders since 1998.
Currently there are three competing technologies for rewritable DVDs
: DVD-RAM, DVD+RW
. DVD-RAM is considered a highly reliable format, as the discs have built-in error control and a defect management system. Therefore, DVD-RAM is perceived to be better than the other DVD technologies for traditional computer usage tasks such as general data storage, backup and archival, though the Mount Rainier Format
standard for DVD+/-RW (and CD-R, CD-RW, DVD+/-R) somewhat lessens the DVD-RAM format's perceived advantage. Curiously, DVD-RAM has a larger presence in camcorders and set-top boxes than in computers, although the DVD-RAM's popularity in these devices can be explained by the fact that it is very easily written to and erased, which for example allows extensive in-camera editing.
The on-disc structure of DVD-RAMs is closely related to hard disk and floppy disk technology, as it stores data in concentric tracks. DVD-RAMs can be accessed just like a hard or floppy disk and usually without any special software. DVD-RWs and DVD+RWs, on the other hand, store data in one long spiral track and require special packet reading/writing software to read and write data discs. It is a common misconception that DVD-RAM uses magneto-optical (MO) technologies, since both DVD-RAM and MO have numerous rectangles on the disc surface. However, DVD-RAM is a pure phase change medium, similar to CD-RW or DVD-RW.
DVD-RAM Cartridge types
|| Bare Disc
|| Non-removable Cartridge
|| Removable Cartridge
|| Empty/No Cartridge
|| double |
| 12 cm
|| yes |
|| type 1
|| type 1
|| type 2
|| type 4
|| type 3
|| type 5 |
| 8 cm
|| yes |
|| type 7
|| type 6
|| type 9
|| type 8 |
Since the Internationale Funkausstellung Berlin 2003 the specification is being marketed by the RAM Promotion Group (RAMPRG), built by Hitachi, Toshiba, Maxell, LG Electronics, Matsushita/Panasonic, Samsung and Teac.The specification distinguishes between
- DVD-RAM version 1.0, recording speed 1x
- Single-sided, one layer discs with a capacity of 2.58 GB
- Double-sided one layer discs with a capacity of 5.16 GB
- DVD-RAM version 2.0, recording speed 2x
- Single-sided, one layer discs with a capacity of 4.7 GB
- Double-sided one layer discs with a capacity of 9.4 GB
- DVD-RAM version 2.1/Revision 1.0, recording speed 3x
- DVD-RAM version 2.2/Revision 2.0, recording speed 5x
- DVD-RAM version 2.3/Revision 3.0, recording speed 6x max
- DVD-RAM version 2.4/Revision 4.0, recording speed 8x max
- DVD-RAM version 2.5/Revision 5.0, recording speed 12x max
- DVD-RAM version 2.6/Revision 6.0, recording speed 16x max
Physically smaller, 80 mm in diameter, DVD-RAM discs also exist with a capacity of 1.46 GB for a single-sided disc, but they are uncommon.
DVD-RAMs were originally solely sold in cartridges; recent DVD recorders can work with discs either with or without cartridge, and many devices do not support cartridges at all. Discs can be removed from cartridges for use with these drives.
Many operating systems like Mac OS (Mac OS 8.6 up to Mac OS X), Linux and Microsoft Windows XP support DVD-RAM operation directly, while earlier versions of Windows require device drivers or the program InCD.
Windows XP can only write directly to FAT32-formatted DVD-RAM discs. For UDF-formatted discs, which are considered faster, compatible device drivers or software such as InCD or DLA are required. Windows Vista can natively access and write to UDF-formatted DVD-RAM discs. This is a non-issue with Linux however, which allows the use of virtually any file system of the multitude that ship with the operating system, including UDF. It is even possible to use the ext3 file system on a DVD-RAM disc. Even though it is possible to use any file system one likes, only very few perform well on DVD-RAM. This is because some file systems frequently over-write data on the disc and the table of contents is contained at the start of the disc.
Mac OS up to 9.2 (Mac OS Classic) can read and write HFS-, HFS Plus-, FAT-, and UDF-formatted DVD-RAM discs directly. Mac OS X officially supports DVD-RAM formatting and writing operations. (See )
Many DVD standalone players and recorders do not support DVD-RAM, especially older or cheaper versions. However, within "RAMPRG" (the DVD-RAM Promotion Group) there are a number of well-known manufacturers of standalone players and recorders that do support DVD-RAM. Panasonic, for instance, has a range of players and recorders which make full use of the advantages of DVD-RAM. There are also a number of video cameras that use DVD-RAM as the recording media.
Some DVD players with hardware DVD-RAM capability are sold without DVD-RAM support. As a specific example, Dell uses the TS-L632D drive manufactured by TSST in some of its laptop computers without DVD-RAM capability. However it is possible, with some difficulty, to replace the firmware with a non-Dell version which supports DVD-RAM.
The newest DVD-RAM Specification, DVD-RAM2 (also called RAM2), is not compatible with DVD drives that do not specifically support reading DVD-RAM2 discs.
Advantages of DVD-RAM
- Long life — without physical damage, data is retained for an estimated 30 years minimum. Ideal for video evidence recording in CCTV applications amongst many other uses.
- Can be rewritten over 100,000 times (DVD±RW can be rewritten approx. 1,000 times). Faster DVD-RAMs support fewer rewrites (3x speed: 100,000, 5x speed: 10,000) , but still more than DVD+RW or DVD-RW. (These are theoretical numbers. In practice they could be smaller depending on the drive, the treatment of the disc and the file system. In practice, a domestic DVD recorder can rewrite a disk only 300 times. Note also that some areas of the disc, e.g. directory, can be written many times without the user perceiving multiple writes.)
- Reliable writing of discs. Verification done in hardware by the drive, so post-write verification by software is unnecessary. Software verification is disabled in all current DVD Video Recorders.
- Disc defect management safeguards data.
- Suitable for archival storage.
- DVD-burning software may not be required — discs can be used and accessed like a removable hard disk. Mac OS (8.6 or later) supports DVD-RAM directly. Windows XP supports DVD-RAM directly for FAT32-formatted discs only. Windows Vista is able to write directly to both FAT32- and UDF-formatted DVD-RAM discs from within Windows Explorer. Device drivers or other software are needed for earlier versions of Windows which do not support UDF, or any format, on DVD-RAM.
- Arguably easier to use than other DVD technology.
- Very fast access of small files on the disc.
- Small 2 KB disc block size wastes less space when writing small files.
- Finalization not necessary. This is an attribute of the VR recording mode and is available on other media such as DVD-RW.
- Media available with or without protective cartridges; can be used in the cartridge by many devices.
- In some video recorders DVD-RAM can be written to and read at the same time, allowing one program to be recorded and a different one, or an earlier part of the same one (time slip recording), to be viewed at the same time. This is an attribute of the VR mode recording mode and is possible, although only at lower bit rates, on other media such as DVD+RW.
- Supported by some high-end security digital video recorders, such as the Tecton Darlex, as a secure export medium. 30 year retention makes this an ideal format for evidence.
- Holds more data when using Double Sided discs than dual-layer DVD+RW and DVD-RW, 9.4GB for DVD-RAM vs 8.5GB for DVD+RW DL and DVD-RW DL.
- Has write-protect tabs to prevent accidental deletion when used in a cartridge.
Disadvantages of DVD-RAM
- Less compatibility than DVD+RW and DVD-RW, despite predating both formats (as noted above).
- 12x media is reportedly available at Audio Cubes II in the USA. It is not reportedly available in Europe. 16x media may not be available anywhere except manufacturers' R&D laboratories.
- DVD-RAM media have always been more expensive than other types of DVD. For example, in May 2008, single 4.7GB DVD+RW or DVD-RW are available for slightly less than US$0.30, whereas the least expensive 4.7GB DVD-RAM was US$1.33.
- DVD-RAM writing will be slower than DVD+RW and DVD-RW until 12x DVD-RAM media becomes available.