Recordable DVD Standards
| 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 standardDVD+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. Table 11.29 compares the competing recordable DVD standards, and Table 11.30 breaks down the compatibilities between the drives and media.
As you can see from looking at both the horizontal rows and vertical columns of Table 11.30, the following factors are worth noting:
DVD+R/RW offers low drive and media prices, provides the highest compatibility with existing formats, and has features that make it the most ideal for both video recording and data storage in PCs. DVD-RAMDVD-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-R, by comparison, is backward compatible with DVD-ROM.) 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. See the section "MultiRead Specifications," earlier in this chapter, for more information. 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-RAM uses what is called the wobbled land and groove recording method, which records signals on both the lands (the areas between grooves) and inside the grooves that are preformed on the disc. The tracks wobble, which provides clock data for the drive. Special sector header pits are prepressed into the disc during the manufacturing process as well. See Figure 11.15, which shows the wobbled tracks (lands and grooves) with data recorded both on the lands and in the grooves. This is unlike CD-R or CD-RW, in which data is recorded on the groove only. Figure 11.15. DVD-RAM wobbled land and groove recording. The disc is recorded using phase-change recording, in which data is written by selectively heating spots in the grooves or on the lands with a high-powered laser. The DVD-RAM drive write laser transforms the film from a crystalline to an amorphous state by heating a spot, which is then rendered less reflective than the remaining crystalline portions. The signal is read as the difference of the laser reflection rate between the crystalline and amorphous states. The modulation and error correction codes are the same as for DVD-Video and DVD-ROM, ensuring compatibility with other DVD formats. For rewriting, a lower-powered laser reheats the spot to a lower temperature, where it recrystallizes. Disc cartridges or caddies originally were required for both single- and double-sided discs but have now been made optional for single-sided discs. Double-sided discs must remain inside the caddy at all times for protection; however, single-sided discs can be taken out of the cartridge if necessary. DVD-RAM specifications are shown in Table 11.31.
DVD-RDVD-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 4.7GBabout seven times that of a CD-Rand 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 (see Figure 11.16). Figure 11.16. DVD-R wobbled groove recording. Table 11.32 has the basic specifications for DVD-R drives.
DVD-RWThe 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:
However, DVD-RW drives still don't support lossless linking, Mount Rainier, or selective deletion of filesall of which are major features of DVD+RW. DVD-RW is currently supported by most major makers of CD/DVD-burning software (including Ahead's Nero, Roxio's Easy Media Creator, and others) and by several drive manufacturers. DVD+RWDVD+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 (MCC/Verbatim), Ricoh, Yamaha, and Thomson, who are all part of an industry standard group called the DVD+RW Alliance (www.dvdrw.com). 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. Table 11.33 lists the basic specifications for DVD+RW drives.
Note that 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, most standard DVD-ROM drives or DVD players can read both DVD+R and DVD+RW media without problems. See the section "DVD+RW Compatibility Mode," later in this chapter, for details. The basic structure of a DVD+RW or DVD+R disc resembles that of a DVD-R disc with data written in the grooves only (refer to Figure 11.16), but the groove is wobbled at a frequency different from that used by DVD-R/RW or DVD-RAM. The DVD+R/RW groove also contains positioning information. These differences mean that DVD+R/RW media offers more accurate postioning for lossless linking, but DVD+R/RW drives can't write to other types of DVD rewritable media. Although some first-generation DVD+RW drives worked only with rewritable media, all current and future DVD+RW drives are designed to work with both DVD+R (writable) and DVD+RW (rewritable) media. The +R discs can be written only once and are less expensive than the +RW discs. Some of the features of DVD+RW includes are as follows:
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 ModeWhen 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:
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). Multiformat Rewritable DrivesBecause of the fragmented nature of the rewritable DVD marketplace, there are two new categories of drives that provide for wider read/write media compatibility:
DVD Multi is a specification developed by the DVD Forum for drives and players that are compatible with all DVD Forum standards, including DVD-R/RW, DVD-RAM, DVD-ROM, DVD-Video, and eventually DVD Audio (DVD+R/RW are not DVD Forum specifications and are not supported). The original version of DVD Multi was published in February 2001; the current version, version 1.01, was approved by the DVD Forum and published in December 2001. The first DVD Multi products for computers reached the market in early 2003. Figure 11.17 compares the DVD Multi logos to the DVD+RW and other DVD forum logos. Figure 11.17. The DVD-R/RAM, DVD-RW, and DVD+RW logos (top left to right), compared to new DVD Multi logos in vertical (lower left) and horizontal variations (lower right). DVD±R/RW, unlike DVD Multi, is not a specification. Instead, it is used to indicate drives that work with both DVD+R/RW and DVD-R/RW media (DVD-RAM is not typically supported by these drives). Such drives usually carry both the DVD-RW and DVD+RW logos shown in Figure 11.17. Thus, DVD±R/RW drives are designed to handle the most common formats supported by the DVD Forum and the DVD+RW Alliance. DVD Multi drives are a good choice for users who have been using DVD-RAM drives but want to enjoy a wider degree of compatibility with the rest of the DVD Forum world. However, if you need to work with the most common types of DVD rewritable media, DVD±R/RW is a better choice. Because of the need to support different read/write technologies, DVD±R/RW drives are more expensive than DVD-R/RW or DVD+R/RW drives. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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