The history of recordable DVD drives is a troubled one. It dates back to April 1997, when the DVD Forum announced specifications for rewritable DVD, DVD-RAM, and DVD-R. Later, it added DVD-RW to the mix. Dissatisfied with these standards, the industry leaders in optical recording and drives formed their own group called the DVD+RW Alliance and created another standard—DVD+R and DVD+RW.

In a war that brings back unhappy memories of the VHS/Beta struggle of the 1980s, as well as the problems in bringing DVD video to light, the computer and movie industries are locked in a struggle to see which enhancements to the basic DVD standard will win out.

DVD-RAM

DVD-RAM is the rewritable DVD standard endorsed by Panasonic, Hitachi, and Toshiba; it is part of the DVD Forum's list of supported standards. DVD-RAM uses a phase-change technology similar to that of CD-RW. Unfortunately, DVD-RAM discs can't be read by most standard DVD-ROM drives because of differences in both reflectivity of the media and the data format.

DVD-ROM drives that can read DVD-RAM discs began to come on the market in early 1999 and follow the MultiRead2 specification. DVD-ROM drives and DVD-Video players labeled as MultiRead2 compliant are capable of reading DVD-RAM discs.

The first DVD-RAM drives were introduced in spring 1998 and had a capacity of 2.6GB (single-sided) or 5.2GB (double-sided). DVD-RAM Version 2 discs with 4.7GB arrived in late 1999, and double-sided 9.4GB discs arrived in 2000. DVD-RAM drives typically read DVD-Video, DVD-ROM, and CD media.

The current installed base of DVD-ROM drives and DVD-Video players can't read DVD-RAM media; most DVD+R/RW and DVD-R/RW drives can't read DVD-RAM media. To improve compatibility with other formats, many recent DVD-RAM drives can also write to DVD-R media, and the DVD Forum has developed a DVD Multi specification for drives that can read/write DVD-RAM, DVD-R, and DVD-RW media.

DVD-R

DVD-R is a write-once medium very similar to CD-R, which was originally created by Pioneer and released by the DVD Forum in July 1997. DVD-R discs can be played on standard DVD-ROM drives. Some recent DVD-RAM drives can also write to DVD-R media.

DVD-R has a single-sided storage capacity of 4.7GB—about seven times that of a CD-R—and double that for a double-sided disc. These discs use an organic dye recording layer that allows for a low material cost, similar to CD-R. To enable positioning accuracy, DVD-R uses a wobbled groove recording, in which special grooved tracks are pre-engraved on the disc during the manufacturing process.

Data is recorded within the grooves only. The grooved tracks wobble slightly right and left, and the frequency of the wobble contains clock data for the drive to read, as well as clock data for the drive. The grooves are spaced more closely together than with DVD-RAM, but data is recorded only in the grooves and not on the lands

DVD-RW

The DVD Forum introduced DVD-RW in November 1999. Created and endorsed originally by Pioneer, DVD-RW is basically an extension to DVD-R just as CD-RW is an extension to CD-R. DVD-RW uses a phase-change technology and is somewhat more compatible with standard DVD-ROM drives than DVD-RAM.

Drives based on this technology began shipping in late 1999, but early models achieved only moderate popularity because Pioneer was the only source for the drives and because of limitations in their performance. Currently, DVD-RW drives are available in 1x DVD-RW/2x DVD-R and the newer 2x DVD-RW/4x DVD-R models.

2x/4x drives have several advantages over older drives, including these:

• Quick formatting. 1x/2x drives require that the entire DVD-RW disc be formatted before the media can be used, a process that can take about an hour. 2x/4x drives can use DVD-RW media in a few seconds after inserting, formatting the media in the background as necessary. This is similar to the way in which DVD+RW drives work.

• Quick grow. Instead of erasing the media to add files, as with 1x/2x DVD-RW drives, 2x/4x DVD-RW drives can unfinalize the media and add more files without deleting existing files.

• Quick finalizing. 2x/4x DVD-RW drives close media containing small amounts of data (under 1GB) more quickly than 1x/2x drives.

However, DVD-RW drives still don't support lossless linking, Mount Rainier, or selective deletion of files—all of which are major features of DVD+RW. DVD-RW is currently supported by most major makers of CD/DVD-burning software (including Ahead Nero Burning ROM, Roxio Easy CD-DVD Creator, and others) and by several drive manufacturers (including Panasonic, Toshiba, and Teac).

DVD+RW

DVD+RW, also called DVD Phase Change Rewritable, is rapidly becoming the premier DVD recordable standard because it is the least expensive, easiest to use, and most compatible with existing formats. It was developed and is supported by Philips, Sony, Hewlett-Packard, Mitsubishi Chemical, Ricoh, Yamaha, Verbatim, and Thompson, who are all part of an industry standard group called the DVD+RW Alliance.

Microsoft joined the alliance in February 2003. DVD+RW is also supported by major DVD/CD creation software vendors and many drive vendors, including HP, Philips, Ricoh, and many remarketers of OEM drive mechanisms. Although DVD-RW has increased in popularity with the advent of faster and easier burning times, DVD+RW is still the most popular rewritable DVD format.

DVD+R, the recordable version of DVD+RW, was actually introduced after DVD+RW. This is the opposite of DVD-RW, which grew out of DVD-R. One of the major reasons for the development of DVD+R was to provide a lower-cost method for permanent data archiving with DVD+RW drives.

And another was because of compatibility issues with DVD-ROM and DVD video players being incapable of reading media created with DVD+RW drives. However, writing DVD+RW media is relatively simple with most drives that can be read by a DVD-ROM or DVD player.

DVD+RW technology is very similar to CD-RW, and DVD+RW drives can read DVD-ROMs and all CD formats, including CD-R and CD-RW. With DVD+RW, the writing process can be suspended and continued without a loss of space linking the recording sessions together. This increases efficiency in random writing and video applications.

This "lossless linking" also enables the selective replacement of any individual 32KB block of data (the minimum recording unit) with a new block, accurately positioning with a space of 1 micron. To enable this high accuracy for placement of data on the track, the pre-groove is wobbled at a higher frequency.

The timing and addressing information read from the groove is very accurate. The quick formatting feature means you can pop a DVD+R or DVD+RW blank into the drive and almost instantly begin writing to it. The actual formatting is carried out in the background ahead of where any writing will occur.

DVD+RW is also designed to work with existing DVD video players, DVD+RW-compatible video recorders such as those made by Philips and Yamaha, and DVD-ROM drives. However, because of the wide variance in equipment, DVD+RW tends to work better in newer equipment rather than in older equipment, particularly set-top players.

As with DVD-RW, you might prefer to use writable (DVD+R) media to improve the odds of compatibility with older drives and players whose compatibility with DVD+RW is unknown. DVD+RW is the format I prefer and recommend, and I expect that in the long run it will be the one preferred by most users.

However, if you need to work with both DVD+R/RW and DVD-R/RW media because of device compatibility, I recommend one of the DVD±R/RW multiformat drives from Sony, NEC, and other vendors. I do not recommend DVD-RAM because it is not supported by set-top players or by most other types of DVD drives.

DVD+RW Compatibility Mode

When DVD+RW drives were introduced in 2001, some users of DVD-ROM and standalone DVD players were unable to read DVD+RW media, even though others were able to do so. The first drives to support DVD+R (writable) media (which works with a wider range of older drives) was not introduced until mid-2002, so this was a significant problem.

The most common reason for this problem turned out to be the contents of the Book Type Field located in the lead-in section of every DVD disc. Some drives require that this field indicate that the media is a DVD-ROM before they can read it. However, by default, DVD+RW drives write DVD+RW as the type into this field when DVD+RW media is used.

The following are two possible solutions:

• Upgrade the firmware in the DVD+RW recorder so it writes compatible information into the Book Type Field automatically.

• Use a compatibility utility to change the contents of the Book Type Field for a particular DVD+RW disc as necessary.

In some cases, the manufacturer of the DVD+RW or DVD+R/RW drive provides a utility as well as a firmware download to perform this task for you. For example, HP includes a compatibility utility with the software provided for the HP DVD200 series and offers it as a download along with updated firmware for the DVD100i drive.

Mode 1 (DVD+RW compatibility bits) is the default with these drives, whereas Mode 2 writes DVD-ROM compatibility bits to DVD+RW media (HP drives mark all DVD+R media as DVD-ROM). If your drive vendor doesn't offer a compatibility utility, check the Compatibility Bitsettings Page at the DVDPlusRW.org for free utilities that work with many DVD+RW drives.

Unfortunately, DVD+RW drives made by Sony don't support third-party bitsetting solutions, and Sony has yet to offer its own solution. If you have problems with Sony DVD+RW media working with DVD-ROM or DVD players, you should try DVD+R media instead.