dvd are read only.
dvd-r; dvd+r and dvd-rw are the re-writeable discs. mostly once only.
DVD Media Formats Explained
There are many different types of writable and rewritable DVD media on the market today. These formats include:
There are also "General Purpose" and "Authoring" discs. DO NOT confuse the "Authoring" media with the term for content development (making / editing what eventually goes on the DVD). The most common type of DVDR is the General Purpose type - if you do not know that you have an actual authoring recorder drive then you most likely have the general purpose type.
is a write-once recordable format which allows excellent compatibility with both standalone DVD-video players and DVD-ROM drives. There are two main types of 4.7GB DVD-R discs: DVD-R for General Use and DVD-R for Authoring. Most consumer drives use the former cheaper General Use discs, while many higher end professional drives use Authoring discs. The correct media type appropriate for the drive must be used when burning. However, once burned, the discs should be able to be read in either drive type. (General Use DVD-Rs are designed to prevent backup of encrypted commercial DVDs).
DVD-RW uses rewritable discs which are rated at more than 1000 rewrites in ideal situations. Unfortunately, DVD-RW does not enjoy the same excellent compatibility with DVD-ROM drives and standalone DVD-Video players that DVD-R enjoys. Another drawback is that unlike DVD-RAM, one must generally erase a DVD-RW disc before reuse.
Most DVD-RW drives should also be able to record to DVD-R. However, the reverse is not true. Many older and some current DVD-R drives are not capable of writing to DVD-RW discs (but may be able to read burned DVD-RW discs). Some drives can also record to CD-R and CD-RW.
Currently DVD-RW and DVD-R are most popular in the multimedia market as well as the general consumer market. For instance the Apple SuperDrive, found in higher end Mac computers used in multimedia creation, is simply a DVD-R/DVD-RW (and CD-R/CD-RW) capable drive.
, like DVD-RW, is a rewritable 4.7GB DVD format. DVD+RW, however, in some ways offers some technical advantages, which for example include: lossless linking (which in turn more readily allows editing of a disc's contents after an initial write while maintaining integrity of the remaining data), currently slightly faster recording speeds, and optional future Mount Rainier drag-and-drop file access support (also known as DVD+MRW). However, DVD+RW does not have the very high compatibility with standalone DVD-video players and DVD-ROM drives that the DVD-R format enjoys. The level of compatibility of DVD+RW is said to be similar to that of DVD-RW. Also, DVD+RW does not currently have the same level of market acceptance as DVD-R.
is a format that only was introduced to the public very recently (early 2002). DVD+R is a write-once 4.7GB format which promises to dramatically increase the compatibility with standalone DVD-Video players and DVD-ROM drives. Whether that claim is fulfilled remains to be seen, but initial reports have been very positive. It must be noted, however, that 1st generation DVD+RW drives do not support DVD+R burning, and it is likely that most cannot be upgraded to do so either. If one wishes to have DVD+R burning functionality, one must purchase a newer drive specifically designed to do so. DVD+R discs currently are somewhat more expensive than DVD-R discs, but prices will likely drop with time. Burners that write to these discs is the HPDVD100i and the DVD-Writer DVD200i drive
Thanks to www.AnandTech.com for this helpful information