DVD-RAM

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.

The term DVD-RAM is a misnomer based on the false assumption that RAM means "read-and-write memory"; the opposite of ROM (Read-Only Memory). However, RAM stands for Random Access Memory (computer chips) and DVDs cannot inherently use the random access method.

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.

Microsoft Windows XP supports DVD-RAM operation directly, while earlier versions of Windows require device drivers or the program InCD. The optical drives in Apple Macintosh computers do not support DVD-RAM operation, but a third party DVD-RAM-compatible drive can be connected and used with software such as DVD Studio Pro.

A DVD format wherein DVD-RAM discs can be recorded and erased repeatedly but are only compatible with devices manufactured by the companies that support the DVD-RAM format. DVD-RAM discs are typically housed in cartridges.

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.

Initially DVD-RAM ( DVD–Random Access Memory) was developed for back-up storage, but later it's capabilities in handling video became evident, so now there are many home DVD-RAM camcorders and DVD-RAM recorders which are aimed to replace VHS.

Although DVD-RAM format was developed by Panasonic in compliance with DVD Forum, it is much different from DVD-R and DVD-RW. The chemical part of the process is essentially the same as in DVD-RW, but the logical part more resembles the operation of hard disk drive. From the very beginning DVD-RAM is divided into several sectors. Data is recorded not in circular track as in normal DVD and CD but is directed in certain sector, without particular order. During reading of the disk this allows to find the desired file fast and easily by addressing appropriate sector. Besides, this layout allows reading and writing information simultaneously. Interestingly enough, DVD-RAM does not require any special software for recording; it can be accessed in the same manner as normal hard drive or floppy disk.

Although DVD-RAM can withstand more writing cycles (about 100000) than DVD-RW, it is substantially more fragile and have to be handled with much greater care. For this reason many DVD-RAM s are being sold in special cartridges, however, if disk is single-sided, it can be removed from cartridge temporarily as some DVD-RAM recorders have normal CD tray instead of cartridge loader.

Some DVD-RAM disks are actually sold without any case at all. These disks require extreme caution during use.

However, despite being extremely fragile, DVD-RAM has most reliable error checking. If error is discovered during burning process, data is simply recorder in different sector; while in any other DVD format disk will become completely unreadable.

Speaking of compatibility, any DVD-RAM recorder will have no troubles reading DVD-R and DVD-RW formats. However, only few drives will be able to read DVD-RAM format. Unfortunately, DVD-RAM is much less common compared to other formats of recordable DVD's and therefore the price for both drives and disks is still relatively high.

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

Long life - without physical damage, data is retained for 30 years minimum.

Can be rewritten over 100,000 times (DVD±RW can be rewritten approx. 1,000 times).

No DVD burning software required – discs can be used and accessed like a removable hard disk. Windows XP supports DVD-RAM directly; earlier versions 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 (where applicable).

In video recorders, DVD-RAM can be written to and watched (even separate programs) at the same time, much like TiVO.

Most DVD recorders do not support DVD-RAM.

DVD-RAM video disks do not play on older DVD players nor on some new models.

The medium is more expensive than DVD±RW.

DVD+RW can be written faster than DVD-RAM when writing large amounts of data.

DVD-RAM is more expensive than other DVD media. Where you can get DVD±RW for about $1 a disc, you'll pay about 4x as much for DVD-RAM discs.
If you're simply archiving data, DVD±R media probably makes the most sense. You can burn at 16x, and since you're archiving, there's no need to choose rewritable media.
If you're doing a regular data backup, DVD±RW is cheaper and almost as fast as DVD-RAM (4x vs. 5x). But you'll be spending a lot more time writing data because DVD isn't a random-write medium.
DVD-RAM wins when it comes to updating your backup, synchronizing the data on your hard drive with your backup set. It only has to erase what's been deleted, add what's new, and replace what's been changed. It doesn't have to rewrite everything.

DVD-RAM is optical storage that:

Is relatively inexpensive

Holds a large amount of data (4.7GB per side at this writing)

Can be re-written hundreds of thousands of times

Has an expected media life of 30 years

Is bootable

Is really ideal for small system backup.