Digital Trends

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.