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(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
there are three competing technologies for rewritable DVDs: DVD-RAM,
DVD+RW and 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 Mt. Rainier standard for DVD+RW
lessens this somewhat. 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
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: DVD-RAM is a pure phase change medium,
similar to CD-RW or DVD-RW.
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.
specification distinguishes between
* DVD-RAM version 1.0, recording speed
Single-sided, one layer discs with a capacity of 2.58
Double-sided one layer discs with a capacity of 5.16
* DVD-RAM version 2.0, recording speed
Single-sided, one layer discs with a capacity of 4.7
Double-sided one layer discs with a capacity of 9.4
* DVD-RAM version 2.1/Revision 1.0, recording
* DVD-RAM version 2.2/Revision 2.0,
recording speed 5x
* DVD-RAM version ?/Revision 3.0,
recording speed 6x max
* DVD-RAM version ?/Revision
4.0, recording speed 8x max
* DVD-RAM version
?/Revision 5.0, recording speed 12x max
version ?/Revision 6.0, recording speed 16x max
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 however also
work with no-cartridge discs – some devices even do not support cartridges
anymore. A cartridge disc is about 50% more expensive than a disc without
operating systems like Mac OS (Mac OS 8.6 or later), Linux and Microsoft
Windows XP support DVD-RAM operation directly, while earlier versions of
Windows require device drivers or the program InCD. The optical drives
shipped with most Apple Macintosh computers do not support DVD-RAM
operation, but a third party DVD-RAM-compatible drive can be connected and
used directly with Mac OS.
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. 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. Mac OS can
read and write HFS, HFS Plus, FAT and UDF formatted DVD-RAM discs
directly. It is possible to use the ext3 file system on a DVD-RAM disc,
but this filesystem was designed for use on hard drives, as a result using
this file system on a DVD-RAM is very slow and prone to corruption. So
while it is possible to use any filesystem 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.
DVD standalone players and recorders do not support DVD-RAM, especially
older or cheaper versions. However, within the 'RAMPRO' (DVD RAM
promotion) group are a number of well-known manufacturers of standalone
players and recorders that DO support DVD-RAM. Panasonic for instance have
an excellent 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.
Long life — without physical damage, data is retained for 30 years
- 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. (Remember, these
are theoretical numbers. In practice they could be smaller depending on
the drive, the treatment of the disc and the file system.)
writing of discs. Verification done in hardware by the drive, so
post-write verification by software is unnecessary.
- Disc defect
management safeguards data.
- Write speed twice as fast (when
verification not enabled) as DVD±RW. (Note: 12x DVD-RAM spec = 16 DVD±RW
spec. As of 7/24/06, DVD±RW write speed was at 8x (DVD±RW specifications)
while DVD-RAM is at 12x (DVD-RAM speed specification).)
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 only for FAT32-formatted discs.
Device drivers or other software are needed for earlier versions of
Windows or if one wants to use the decidedly better UDF format rather than
- Easier to use than other DVD technology.
- Very fast access
of smaller files on the disc.
- 2 KB disc block size wastes less space
when writing small files.
- Finalization not necessary.
available with or without protective cartridges.
- In video recorders,
DVD-RAM can be written to and watched at the same time, much like
- Supports time slip recording and recording without border
Less compatibility than DVD+RW and DVD-RW
- 12x media is not readily
available in the USA and will not be available in the US and Europe in the
near future due to low market demand. 16x media may not be available
anywhere except manufacturers' R&D laboratories.
- DVD-RAM media is
more expensive than other DVD types. 12x media is expected to cost almost
$9 per disc, at least initially, but this price will fall as production
- DVD-RAM writing will be slower than DVD+RW and DVD-RW until
12x DVD-RAM media becomes available. If write verification is enabled, the
writing speed is decreased by about half. Using FAT32 instead of UDF may
also slow DVD-RAM performance.
Wikipedia information about
DVD-RAM. This article is licensed under the GNU Free Documentation License . It uses material
from the Wikipedia article 'DVD-RAM'
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