Here is some information I just found on
http://www.anandtech.com/guides/viewfaq.html?i=118
The differences between the different types of DVD Re-Write Formats.
Date: Oct 6, 2003
Category: General Hardware
Author(s): Eug
Currently there are many writeable and rewriteable DVD formats on the
market, and this can be confusing to the average consumer. These DVD formats
include:
DVD-RAM
DVD-R
DVD-RW
DVD+R
DVD+RW
DVD-RAM
DVD-RAM is a sanctioned format of the DVD Forum, a consortium of companies
involved in the development of DVD standards. DVD-RAM was a format
originally aimed primarily as a data solution, but it is now becoming
popular as a video format used by some brands of standalone (non-PC) DVD
recorders. DVD-RAM is a very robust data storage solution, theoretically
allowing greater than 100000 rewrites per disc.
Early PC-based DVD-RAM recorders used 2.6 GB discs (or double-sided 5.2 GB
discs), but current drives also use 4.7 GB discs (or double-sided 9.4 GB
discs). DVD-RAM discs are traditionally housed within cartridges, so that
the media is well-protected. Originally, the cartridges could not be opened,
but newer Type II and Type IV cartridges can be opened, an important feature
for those who wish to read these discs in DVD-RAM compatible DVD-ROM drives
or standalone DVD players. In addition, some DVD-RAM discs are now sold
without cartridges.
In addition to support of the usual DVD UDF formats, DVD-RAM also allows
fully integrated OS-level random read/write access similar to hard drives,
with both Windows XP (with FAT32) and Mac OS X (with FAT32 or HFS+), as well
as on-the-fly write verification.
The main drawback of the DVD-RAM format is its limited read compatibility by
DVD-ROM drives and standalone DVD players. DVD-RAM read support with these
units is increasing however, partially because of the increasing popularity
of home standalone DVD-RAM recorders in home theatre systems.
DVD-R and DVD-RW
DVD-R and DVD-RW are also both formats of the DVD Forum. Both formats
generally use 4.7 GB discs, although some professional DVD-R drives use 3.95
GB discs.
DVD-R is a write-once recordable format which allows excellent compatibility
with both standalone DVD players and DVD-ROM drives. There are two main
types of DVD-R discs: DVD-R for General Use and DVD-R for Authoring. Most
consumer DVD-R burners use the cheaper General Use discs, while some
professional burners use Authoring discs. The correct media type appropriate
for the recorder must be used when burning a DVD-R. However, once written,
the discs should be readable in either drive type. (General Use DVD-R is
designed to prevent backup of encrypted commercial DVDs.)
DVD-RW media uses rewriteable discs which are rated for more than 1000
rewrites in ideal situations. The majority of standalone DVD players will
play video recorded on DVD-RW discs, but the compatibility is not as high as
with DVD-R.
Current DVD-RW recorders also record to DVD-R. However, the reverse was not
always true. Some older DVD-R recorders were not capable of writing to
DVD-RW discs (although some were able to read DVD-RW discs burned with other
drives).
DVD-RW and DVD-R have heavy penetration into the professional multimedia
market as well as the general consumer market. For instance, the Apple
SuperDrive, found in many pro and consumer Mac computers, is simply a
DVD-R/DVD-RW (and CD-R/CD-RW) capable burner.
DVD+R and DVD+RW
These two formats are backed by the DVD+RW Alliance. While these formats are
not supported by the DVD Forum, several members of the DVD+RW Alliance are
also members of the DVD Forum. These discs are very similar to DVD-R and
DVD-RW in design, usage, and compatibility.
DVD+RW, like DVD-RW, is a rewriteable 4.7 GB format, and overall it has
similar functionality to DVD-RW. The level of compatibility of standard
DVD+RW discs in standalone DVD players is similar to that of DVD-RW. The
rewritability of DVD+RW is also said to be similar to that of DVD-RW,
allowing up to 1000 rewrites.
One potential advantage of the DVD+RW format is Mount Rainier (DVD+MRW)
drag-and-drop file access support planned for Longhorn, a future version of
Windows slated for release in 2005. Older DVD+RW drives do not support this
function, but newer drives may. While DVD+MRW is arguably not as robust a
data solution as DVD-RAM, DVD+MRW potentially will offer higher read
compatibility in current DVD-ROM drives.
DVD+R is a format that was introduced to consumers in early 2002. The first
generation +RW recorders did not support DVD+R recording, and likely cannot
be upgraded to do so. However, all current models of DVD+RW recorders also
support DVD+R recording. Compatibility of +R discs in standalone DVD players
is similar to that of DVD-R.
Can I have it all?
Support of combinations of several of the formats are available in many
current drives. Recorders that conform to the DVD Forum's DVD Multi Recorder
standard will record to DVD-RAM, DVD-R, and DVD-RW. Other recorders also
record to both +R/+RW and DVD-R/DVD-RW. Some drives are even able to record
to all of the DVD Forum and DVD+RW Alliance formats. In addition to the
various DVD formats, most drives will also record to CD-R and CD-RW discs.
So what should I buy then?
This is a very difficult question. The choice largely depends on one's usage
environment and preferences.
DVD-RAM discs cannot be used in most standalone DVD players and DVD-ROM
drives, and this has historically made this format less attractive for the
average home user. However, the integrated OS-level drag-and-drop read/write
data support of DVD-RAM makes it very attractive for some users, especially
now that most current DVD-RAM burners also support DVD-R burning for video
applications. DVD-RAM capable PC drives will also be ideal for those whom
already own DVD-RAM based camcorders or standalone DVD-RAM recorders.
DVD-R/DVD-RW drives currently have the highest market penetration, both with
PCs and Macs. As previously mentioned, DVD-R enjoys high compatibility with
standalone DVD players. In addition, the low cost of DVD-RW is attractive to
many for backup purposes. Furthermore, most standalone DVD players will read
DVD-RW as well, although the compatibility rate is lower than with DVD-R.
DVD+R/DVD+RW is gaining market share, and these discs appear to have similar
compatibility on standalone DVD players as DVD-R/DVD-RW discs. Similarly,
current functionality with these drives is similar to DVD-R/DVD-RW drives,
both for data and for video applications, and they likely are equally
reliable.
And of course, as mentioned earlier, many multiformat drives exist (albeit
often at higher cost).
What about external DVD recorders?
DVD recorders exist in SCSI and IDE formats. Most external DVD recordable
drives are essentially IDE drives with USB 2 or Firewire 1394a bridges and
custom housing. These drives can be purchased as complete drives, but one
may purchase a standard IDE DVD burner for use in a third party USB 2 or
Firewire enclosure. Besides ease of installation, an external drive offers
the ability to use a single drive with multiple computers.
Compatibility of external drives is not guaranteed with all software,
however.
Can I record DVDs with my laptop?
Yes! Some laptops now include DVD burners as the primary optical drive. If
one does not have an internal DVD burner, one may use an external drive,
connected to a Firewire or USB 2 port on the laptop. This port can be either
built-in or on an add-in PCMCIA adapter card.
How fast can I burn my discs?
The fastest desktop burners (as of September 2003) are 8X for DVD+/-R and 4X
for DVD+/-RW. Laptop DVD burners usually have a 2X maximum DVD burn speed.
Can I use a DVD burner to make backups of commercial DVDs?
Making backups of DVDs one does not own or making backups for resale is
illegal. However, it may be legal to make backups of one's own DVDs for
personal use. For example, some families may wish to backup children's DVDs,
in order to protect them from damage caused by mishandling.
Many may be familiar with the process of CD backups, which simply involves a
direct copy of a CD to a CD-R. Unfortunately, the backup process for DVDs is
usually a much more complex process, for a number of reasons.
1.. Most DVDs have encryption. In order to backup the video data on a DVD
(which is located in the VIDEO_TS folder), one must first decrypt the disc
to a computer's hard drive. Various software exists on various platforms to
perform the decryption.
2.. Most commercial DVDs utilize dual-layer discs, which can hold more
than the 4.7 GB of a single DVD recordable disc. Both layers of dual-layer
discs are readable by a DVD player's laser from one side of the disc. (In
contrast, double-sided discs must be flipped over in order for a DVD player
to read both sides.) Unfortunately, while double-sided DVD recordable discs
do exist, dual-layer DVD recordable discs do not. Thus, in order to backup a
dual-layer disc, one must either compress or reencode the video data to fit
on a single 4.7 GB DVD, remove various portions of the disc (such as
trailers or extra audio tracks), or else split the disc onto two DVDs.
Various software is available to perform these functions, and some will
allow one to keep all the original menus and titles. Note that if the video
is simply extracted and burned to a disc as a video data file, a DVD player
will not recognize the disc. In order for a disc to be read in a DVD player,
there must be proper formatting of the data within the VIDEO_TS folder.
3.. Care must be given to ensure that the burning software is configured
properly to create discs for DVD Video. If the burning software is set to
wrong type of DVD file system, the disc will not be recognized by standalone
DVD players (even if the disc is playable on a computer).
How come my 4.7 GB disc isn't really 4.7 GB?
Like hard drives, 1 GB on a DVD recordable disc equals 1 000 000 000 (109)
bytes. In contrast, a computer considers 1 GB to be 1 073 741 824 (230)
bytes. Thus, a 4.7 GB disc is seen by a computer as having approximately
4.37 GB.
