Range Of Available Standards
When the CD-R was launched, it only came in one version, whereas the DVD comes in three recording formats: DVD-RW, DVD+RW and DVD-RAM. The last of these was developed over ten years ago and is mainly designed to be a professional storage medium. They come in the form of cartridges that are inserted into the burner. This, of course, is a format incompatible with DVD-ROM drives, and even less so with home players, so it's on its way out, to be replaced by the other two formats: DVD-RW and DVD+RW.
DVD-RW
On the one hand, we have the forerunner Pioneer, who, in accordance with DVD Forum (the entity which controls the DVD name and technical aspects), developed the DVD-RW.
DVD+RW
On the other hand, there is DVD+RW Alliance , where, among others, we find HP, Philips, Ricoh, Sony, Thomson and Yamaha. They officially claim to have developed a new format because the DVD-RW cannot handle video recording very easily. But it may be that they just don't want to pay royalties to DVD Forum.
The Differences
There is very little difference between DVD-R and DVD+R, both of which can only be written once. They are used in exactly the same way. But you have to be careful with DVD-R because there are two standards for blank disks. The one to use is marked "DVD-R for General Use." The other is marked "DVD-R for Authoring," and it only works for mastering DVD video or data because its composition is different. This sort of DVD-R is not usually available to the general public.
Things get a bit more complicated with DVD-RW and DVD+RW. DVD-RW technology is very similar to that of the CD-RW. For DVD+RW, the Alliance wanted to make video recording easier, especially for home use. So they implemented a technology called Lossless Linking. In DVD+RW video format, a video can be encoded in VBR (variable bit rate). The process of writing at a constant rate takes up a lot of room, so it has to be stopped and started again. This is likely to cause link loss, which makes the disk incompatible with read-only devices like DVD video players. With DVD+RW, the process can be stopped and started again without any link loss. This characteristic makes the format efficient and suitable for random data writing and video applications. With lossless linking, it is also possible to replace any individual block of 32 kB (write unit) with another, without losing compatibility.
For a lossless link, each block of data must be written in the right place with precision (on 1 micron). For this, the groove is controlled by a high-frequency wobble (817 kHz at n=1) to ensure that writing stops and starts in an exact position. The writing clock resulting from the groove is very precise. At the same time, addressing information is stored in the spiral groove by locally inverting the radial wobble mark. There are four addresses per ECC block of 32 kB, so the address format is reliable with wide margins of detection.
