Guide to DVD Media

Introduction

The ability to hold a movie or several episodes of your favorite television with crystal clear picture and full surround sound has transformed how we enjoy our entertainment centers. Unfortunately, the specifications of this media are not as clear as the picture it provides. There are numerous, non-compatible, often conflicting formats currently in use. One of the problems here is the merger of the home theater with the computer. DVD is the central point between the two and has to accommodate both types of systems. There is also a variety of reasons for DVD drives. While the one that comes to mind first and foremost is viewing movies there is also data storage, music and editing your only multimedia endeavors. At first glance all DVDs might seem the same but they are not all created equally.

Commercial DVDs

This is the familiar DVD that we buy and play on our home theaters or DVD drives in our computers. Like most DVDs it may look like a regular CD, 120mm in diameter, but that is about where the similarity ends. This DVD uses a different laser to read the information. A CD uses 780 nm (infra red light) where the DVD has a laser of 640 nm (red light). This allows for a finer focus and more data on the disc. The pits that the laser reads is also different, 0.834 microns for the CD versus 0.40 microns. All this translates into the greater data density 0.68 GB on the CD and 4.7 GB for the DVD. Add to this the fact that there is only one layer for the CD but 1, 2 or even 4 in use on the DVD. This adds up to about two hours of high quality audio and video per side, up to eight hours on a DVD-18, a disc with two layers on each of the two sides. If you look at the DVD if it is silver in color its one layer, gold for two layers. On many players there is a slight pause when the player moves from one layer to the next.

DVD-ROM

Basically this is a large data drive readable by most DVD drives. On commercial discs it provides video games, web links, scripts and other extras. Many DVD players cannot read this data, it usually requires a computer based DVD player like WinDVD or Interactual. More and more DVDs out on the market have DVD-ROM information embedded on them.

DVD-RAM

This format transforms your DVD drive into a virtual hard disk. It has capacities of 2.6GB or 4.7GB for single sided discs and 5.2GB or 9.4GB for double sided discs. They reportedly can be re-written about 100,000 times. They can not be used in your home theater DVD player and do require a DVD-RAM compatible drive on your computer.

DVD-R

This is a write once format, after you burn a DVD in this format it is permanent. There are two variations of this format, DVD-RA (authoring) and DVD-RG (general). The authoring format is used to create professional master copies of something that will wind up on a commercial DVD. This is called a Cutting Master Format (CMF). The general variation is used for small scale distribution and achieving files for home or small business use. The DVD-RA uses a 635 nm laser, the DVD-RG a 650 nm. Depending on the specifications of the home theater DVD player you can usually play a DVD-R disc. Some older models of home units are not able to play them so check your design specifications if you are interested in this format. It is good for transferring home movies to DVD, creating your own DVD presentations and other applications. A DVD-R disc will usually play on a home machine and can be read by a DVD-RAM or DVD+R drive. It can only be written on by a DVD-R drive.

DVD-RW

There is a variation of the DVD-R format that can be re-written. The DVD-RW format is similar to the write once format but can be re-written about 1,000 times. This format can be read by most modern DVD players and most other DVD drives in your computer. Because of how a DVD-RW is written some drives may think it is dual layer when it’s not and will refuse to play it. A DVD-RW drives write DVD-R, DVD-RW, CD-R, and CD-RW discs. These discs have a 4.7 GB capacity and are one sided. You can write to this format in several sessions as long as the disc is not finalized. When finalized it becomes a DVD-R disc and must be reformatted to write to it again. This will erase the information already on the disc.  Both DVD-R and DVD-RW use the Constant Linear Velocity (CLV) method of writing data. This method is suited to streaming video. CLV rotates the disc at different speeds depending on the track, fastest with tracks on the outer part of the disc. This can result in slower random access to what is on the disc, not a problem for discs that are intended to be played from the beginning to the end.

DVD+R

This is another form of the write once DVD. It also has a capacity of 4.7 GB and can also be played on most modern home DVD players and computer DVD drives. If you need or want both DVD-R(W) and DVD+R(W) you will need a combination drive that supports both the formats. Typically the DVD+R disc can be read at faster speeds that the DVD-R counterparts. While this is not particularly important for viewing a program it will matter if you plan to use it for data storage. The reason for this is the DVD+R uses the Constant Angular Velocity (CAV) method of storage. It is considerable fast at random access than the CLS method.

DVD+RW

Of course, there is a re-writable version of the DVD+R format. The specifications are the same as the read only one. The main thing here is this format is best suited to applications where you want to have an incredibly large floppy disc. It can act as a 4.7 GB removable hard drive and is great for system backups. The originally stated function of this format was data bit more but more programs are using it for home video applications. Unless you have a high end DVD drive you will have some problems with playing this disc on a drive made for DVD-R formats. An increasing number of newer drives are supporting both formats as well as many home theater DVD players. DVD+RW incorporate what is called lossless linking technology. This permits you to use the drive much like a video recorder. You can stop and start the session with a great degree of accuracy and replace individual 32kB data blocks. This makes it ideal for drag and drop applications and makes the drive as easy to use for data as a regular hard drive. As with other RW formats you need to finalize the disc to play it in most home DVD players. Once the disc is finalized it requires a full, destructive format to write to it again. Typically it can be re-written about 1,000 times.

The Future of DVD

The next step in DVD technology is high definition DVD or HD-DVD. Right now there are at least four different, non-compatible formats trying to make it to the top of the heap. If you are old enough to remember the VHS/Beta wars when video tape first came out that pales in comparison to what is happening with DVDs. The front runners so far are:

  • HD-DVD-9:  uses a red 650 nm laser like current DVDs. Instead of the current MPEG-2 compression it will use a proprietary new codec. The ROM version is slated for 8.5 GB with a bit rate of 11 mps in contrast to the 10 mps of the current commercial DVD. Shorter films can be set to up to 1080i resolution
  • Advanced Optical Disc (AOD): This employs a blue-ultraviolet laser in the 405 nm range and will hold up to 15 GB of data per side in ROM mode or 20 GB for a film. The same data depth (how deep the actual layer is) is still 0.6mm like current DVDs. The bit rate is 36 mps. It is being pushed by Toshiba and NEC.
  • BluRay: This format will hold up to 27 GB per side and has a data depth of 0.1mm. If the dual layer format takes hold you can potentially have up to 50 GB on a disc. This will provide about 10 hours of audio/video in standard definition and a bit rate of 4.7 mps. Again, a 407 nm laser is used.
  • Blue-HD-DVD-1 and Blue-HD-DVD-2: These are formats similar to the Blu-Ray but are being explored by Taiwan’s Industrial Technology Research Institute. The ‘1′ version uses a 0.6 mm data depth while the ‘2′ has the tighter 01 mm. Both use a 405 nm laser.

One of the main concerns of all these new formats is to make them backward compatible to current DVD standards, this way your current collection of discs will not instantly become little more than coasters. The formats themselves are not compatible with each other so the industry, and the consumer, will have to make some decisions before any of these formats become popular. There is little doubt that RW versions of the top contenders will come out in the future making for even more variations, alterations and combinations to confuse the end user.

With all these choices it is best to consider what you expect from your DVD, whether it’s for data storage or making your own home movies (remember there are copyright laws) choose wisely or at least go for the drive that supports the most formats currently available.

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