Getting familiar with recordable DVD formats
Probably everyone nowadays had a need to transfer information between several PC's or make a backup copy of favorite movie. Recordable DVDs (DVD-Rs) serve this purpose very well, but it could be quite hard to get familiar with all the different types of them. While in CD era there were only two formats, namely CD-R for recordable and CD-RW for rewritable disk, for DVD it is not that simple. The fight between manufacturers to enforce their own formats led to the mess of the biblical scale. Besides DVD-R and DVD-RW, in most shops it is possible to encounter DVD+R, DVD+RW and even mysterious DVD-RAM. And there is no guarantee that your DVD drive will be able to work with newly purchased disk.

In this article we will try and help users to get familiar with this mess.

DVD-ROM
(DVD Read Only Memory). Generic factory-printed DVD. All mass-production DVDs with movies, software etc are printed on DVD-ROM.

DVD-R
(DVD-Recordable - pronounced as "DVD Are" or "DVD Dash Are"). This is the first format for recordable DVDs. It was developed in 1995 by Pioneer and was approved by DVD-Forum as a main standard for recordable DVD. Basically, this formatis direct analogue of CD-R but with bigger capacity and, respectively, smaller track size. As with CD-R, record is made by altering the structure of organic polymer in reflective layer with powerful laser. DVD-R can be recorded only once, but it is compatible with most DVD players and computer DVD drives. Properly stored and unscratched DVD is believed to remain readable for hundreds of years.

Initially DVD-R was only single-layered, but recently double-layer DVD-R DL (dual layer) becomes available. They are also known as DVD-R9, however, they are still uncommon and they can be recorded only on newest models of DVD burners. Trying to record these disks in non-compatible drive can actually lead to the DVD burner damage.

There are two types of DVD-R disks: DVD-R Authoring (DVD-R (A)) and DVD-R General (DVD-R (G)).DVD-R (A) type of disks appears first and was used only for professional needs. This type of disk allows recording of anything, including hidden area and keys, which means that It can be used as a master-copy for mass-production.

Devices and disks compatible with DVD-R(A) are professional equipment and therefore very expensive and uncommon.

DVD-R General (G) is much more common. It was developed later specifically for the needs of common users. This type of disks does not allow making a full copy of protected DVD - no keys will be recorded and resulting disk simply will not play. On the other hand, there are lots of devices and blank DVD-R son the market for this type of disks, and they also quite inexpensive. DVD-R (G) devices can read DVD-R (A) disks but cannot record anything on them.

Unlike CD-R, DVD-R shave a special copy protection called CPRM, which stands for Content Protection for Recordable Media. Each blank DVD-R has inerasable encrypted entry (lead in) in hidden area of the disk, which contains information about type of medium and manufacturer. When backup copy of protected DVD is made, copy program will re-encode the information again, but this time using this hidden information, so twill not be possible to copy the resulting disk again as it will require hidden information from specific medium. This type of copy protection also supported by other DVD-Forum formats, namely DVD-RW and DVD-RAM.

DVD-RW
DVD-RW (DVD ReWritable) was also developed by the Pioneer and essentially is the same DVD-R with only difference that reflective layer's state can be transformed by the laser more than once. The specifications for DVD-RW states that each DVD-RW medium should withstand up to 1000 rewriting cycles. The reflectivity of < b>DVD-RWs is much less then of DVD-R and some DVD drives can mistake them for dual-layer DVD. For this reason DVD-RW are compatible with only approximately 70% of existing DVD players.

Early models of DVD-drives required DVD-RW to be finalized in order to read it properly; however, with the appearance of new drives this is not necessary anymore in most cases. It is also not necessary to write at least 1 GB on a disk. Files of any size, no matter how small can be recorded now.

Dual layer DVD-RW, called DVD-RW DL with capacity up to 8.54GB of data is about to appear soon. Currently it is being developed by Ricoh; unfortunately, it won't be compatible with current DVD-drives and for this reason is unlikely to ever become popular. Besides, high capacity Blue-Ray and HD DVD are also coming soon.

DVD+RW
Despite the decision of DVDForum, DVD+RW (DVD ReWritable, pronounced as DVD plus R) format was founded and promoted by coalition of developers called DVD+RW Alliance. First version of DVD+RW, presented in 1997, was able to hold only 2.8 GB of data (compared with 4.7 for DVD-RW). These disks also weren't compatible with normal DVD players and, basically, all of these were the reasons for DVD Forum not to accept this standard.

later developers managed to improve both flaws but even after this, DVD+RW didn't become a standard. As a result, DVD+RW can only reviewed a potential alternative to DVD-RW. However, DVD+RW is not without some pleasant features that DVD-RW misses:

1. Lossless linking technology allows editing of the recorded disk on sector level, which means that, unlike in DVD-RW, there is no need to rewrite whole disk when only certain parts of it needs to be changed.

2. DVD+RW format has better facility for error handling. If certain sector wasn't recorded properly, it is rewritten again, more carefully. Also during the process of disk creation DVD Burner is able to determine the address of sector that is being recorded, so if the record process is interrupted, it is possible to resume it from the same position where it stopped.

3. DVD+RW format supports EasyWrite(Mt. Rainier) technology, which in conjunction with special software such as DirectCD or InCD allows using DVD+RW medium as a normal floppy or hard drive via Explorer or other file manager. The support for EasyWrite also will be included in new Microsoft Windows Vista as a standard option.

4. In addition to everything above, maximum writing speed for DVD+RW is about twice faster than for DVD-RW.

However, DVD+RW format also has some drawbacks.For example, DVD+RW is less compatible compared to DVD-RW, and the probability of running into incompatible DVD drive is higher, no matter what the press-releases and advertisements claim. Compatibility becomes even bigger issue for old DVD drives. DVD+RW and DVD+R have a special protection system designed for them, called VCPS (Video Content Protection System for DVD+R/+RW). It has all the features of CPRM (which is for DVD-RRW) and also supports limitations in copying of protected digital broadcasts. However, such innovations are usually welcomed only by movie and video producers and generally provide only nuisance for users.

DVD+R
Although it might seem strange, DVD+R was introduced by the same DVD+RWAlliance later than DVD+RW, namely in 2002, which is the reason why it is possible to encounter DVD drives that can work with DVD+RW but are totally incompatible with DVD+R. The introduction of DVD+R was more of a step back for the developers, as the only thing they have to do to create DVD+R is to change the substance in reflective layer of DVD+RW from rewritable to the one that support only one cycle of writing. Due to this, DVD+R is actually missing some of useful features of DVD+RW, such as improved error handling. There is also dual layer version of DVD+R, called DVD+R DL or DVD+R9 (actually, it appeared earlier thanDVD-R9). In general, DVD+R does not differ much from DVD-R.

DVD-RAM
Initially DVD-RAM (DVD-Random Access Memory) was developed for back-up storage, but later it's capabilities in handling video became evident, so now there are many home DVD-RAM camcorders and DVD-RAM recorders which are aimed to replace VHS.

Although DVD-RAM format was developed by Panasonic in compliance with DVD Forum, it is much different from DVD-R and DVD-RW. The chemical part of the process is essentially the same as in DVD-RW, but the logical part more resembles the operation of hard disk drive. From the very beginning DVD-RAM is divided into several sectors. Data is recorded not in circular track as in normal DVD and CD but is directed in certain sector, without particular order. During reading of the disk this allows to find the desired file fast and easily by addressing appropriate sector. Besides, this layout allows reading and writing information simultaneously. Interestingly enough, DVD-RAM does not require any special software for recording; it can be accessed in the same manner as normal hard drive or floppy disk.

Although DVD-RAM can withstand more writing cycles (about 100000) than DVD-RW, it is substantially more fragile and have to be handled with much greater care. For this reason many DVD-RAMs are being sold in special cartridges, however, if disk is single-sided, it can be removed from cartridge temporarily as some DVD-RAM recorders have normal CD tray instead of cartridge loader.

Some DVD-RAM disks are actually sold without any case at all. These disks require extreme caution during use.

However, despite being extremely fragile, DVD-RAM has most reliable error checking. If error is discovered during burning process, data is simply recorder in different sector; while in any other DVD format disk will become completely unreadable.

Speaking of compatibility, any DVD-RAM recorder will have no troubles reading DVD-R and DVD-RW formats. However, only few drives will be able to read DVD-RAM format. Unfortunately, DVD-RAM is much less common compared to other formats of recordable DVD's and therefore the price for both drives and disks is still relatively high.

DVD+VR, DVD-VR
DVDs can be recorded in two modes - Video Format and Video Recording Format (DVD-VR). First one is compliant with DVD-Video standard and is compatible with any equipment (this format is used for factory DVD-Video disks and for video data on DVD-R). DVD-RV mode can be altered after recording and does not require copy to hard drive in order to edit disk contents. It is possible to add, cut and delete video data for the disks written in DVD-VR mode, it is also possible to add more chapters or change menu. This can be done for both DVD-RW and DVD-RAM (for DVD-RAM it is actually the only available mode).

For DVD+RW there exists slightly better version of DVD-VR called DVD+VR. Some of the positive differences from DVD-VR are the possibility of creation of full-fledged menus up to 30megabytes in size, while DVD-VR can only generate standard play-lists. It is also possible to delete data from DVD+VR anytime, while in DVD-VR it has to be done only prior to recording of new data. And the most important thing - DVD-VR disks can only be played on DVD Burner or home DVD Recorder, while DVD+VR can be viewed on any device capable of reading DVD+RW.

Not long ago the selection of preferred format was an important question, as after selecting, for example, DVD-R compatible device the user have to live with the fact that the device won't be able to read or write DVD+R. It was also dangerous to use DVD-RW or DVD+RW as a floppy to transfer data, because, unlike CD-RW, there was a chance that there will be incompatible drive in other computer.

Luckily enough, these problems are now gone.

Summary
After the appearance of first multi-format device on the market, any modern DVD drive now supports almost all of available formats, and the selection of desired type of DVD can be made several times a day, depending on particular task. The only sad thing that the mess with DVD formats was sorted too late, as completely new formats of disks are already emerging.