DVD-RAM

From Free net encyclopedia

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.

1 Introduction
2 Specification
3 Compatibility
4 Name
5 Comparison
- 5.1 Advantages of DVD-RAM
- 5.2 Disadvantages of DVD-RAM
6 See also
7 External links

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Introduction

Compared with other writeable DVDs, DVD-RAM is more closely related to hard disk technology, as it has concentric tracks instead of one long spiral track. Unlike the competing formats [[DVD+R]], DVD-R, [[DVD+RW]] and DVD-RW, special DVD burning software is not required to write or read DVD-RAMs on a computer. DVD-RAMs can be accessed like a usual floppy disk or hard drive.

Specification

Image:DVD-RAM FUJIFILM Disc-removalble Without cartridge-locking-pin.jpg 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. DVD-RAM is considered a highly reliable format, as the discs have built-in error control and a Defect management system. 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.

Image:Mini-DVD-RAM with Holder.jpg The specification distinguishes between

DVD-RAM 1.0
- 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 2.0
- Single-sided, one layer discs with a capacity of 4.7 GB
- Double-sided one layer discs with a capacity of 9.4 GB

Physically smaller DVD-RAM discs also exist with a capacity of 1.46 GB, 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 cartridge.

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Compatibility

Many 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 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.

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. 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 you like, 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-RAM isn't supported for most DVD standalone players and recorders, especially those of older versions.

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Name

Some people don't like the RAM part of the name DVD-RAM, because a DVD-RAM (like a hard disc drive) is not really Random Access Memory. The random access capabilities of DVD-RAMs are much better than those of other writable CDs or DVDs. The name is good for comparision with formats like [[DVD+RW]] or DVD-RW, but not useful for comparision with semiconductor memory. Discuss the naming on the discussion page.

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Comparison

Currently there are three competing formats for rewritable DVDs: DVD-RAM, [[DVD+RW]] and DVD-RW.Image:Dvdramopen2.gif DVD-RAM is more suited to data backups and use in camcorders than DVD±RW.

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Advantages of DVD-RAM

Long life — without physical damage, data is retained for 30 years minimum. However it is suspected that it is just a theoretical claim without firm proofs.
Can be rewritten over 100,000 times (DVD±RW can be rewritten approx. 1,000 times). Faster DVD-RAMs support less rewrites (3x speed: 100,000, 5x speed: 10,000) , but still more than DVD±RW.

(Remember, this are theoretical numbers. In practice they could be smaller.)

No DVD burning software required – discs can be used and accessed like a removable hard disk. Windows XP and Mac OS (8.6 or later) supports DVD-RAM directly; earlier versions of Windows need device drivers or InCD.
Very fast access of smaller files on the disc.
Automatic hardware verification of written data, no need to verify manually via software.
Robust plastic cartridge protects the disk, similar to a CD Caddy (where applicable).
In video recorders, DVD-RAM can be written to and watched (even separate programs) at the same time, much like TiVO.
Supports time slip recording and recording without border in/out writing
Finalization not necessary

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Disadvantages of DVD-RAM

Type 2 discs do not always come in a case (which can be considered an advantage since they can be used in the same player as other DVD types).
Most DVD recorders (old or new) do not support DVD-RAM.
Most DVD standalone players (old or new) cannot read DVD-RAM.
DVD-RAM is more expensive than other DVD types. Lowest price for a set of 10 discs in Germany is about 5 € for DVD±R, 12 € for DVD±RW and 25 € for DVD-RAM (April 2006).
DVD+RW can be written faster than DVD-RAM when writing large amounts of data. Especially when considering that most DVD-RAM devices have write verification enabled by default, which essentially cuts the writing speed in half.
Note that with the release of 12x speed DVD-RAM in Japan and the pending release of 16x DVD-RAM, this statement may no longer be correct.

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