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Home > Optical Storage > DVD-RAM Drives > Introduction To DVD-RAM Optical Storage Technologies
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This page provides an extensive overview of what DVD-RAM Storage mediums are and how they can be used in desktop computers.
 
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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-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. Although the MultiRead2 logo is not used on current products, some recent and current DVD-ROM drives can read DVD-RAM media; check the specification sheet for a particular drive to verify compatibility.

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. Although DVD-ROM drives, older DVD+R/RW and DVD-R/RW drives, and DVD-Video players can't read DVD-RAM media, DVD Multi and DVD Super Multi drives can read/write DVD-RAM.

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 11.13, 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.

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 and are seldom used today. 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.

Table 1.1

DVD-RAM Specifications

Storage capacity

2.6GB single-sided; 5.2GB double-sided

Disc diameter

80mm-120mm

Disc thickness

1.2mm (0.6mm×2: bonded structure)

Recording method

Phase change

Laser wavelength

650nm

Data bit length

0.41-0.43 microns

Recording track pitch

0.74 microns

Track format

Wobbled land and groove

In the past, I have been opposed to DVD-RAM because of a lack of compatibility with other drive types. However, if you use drives supporting the DVD Super Multi standard, you can read and write DVD-RAM as well as other rewritable DVD formats. With the ability to read, write, and erase data without the need to use UDF packet-writing software, DVD-RAM can be a useful alternative to other types of rewritable DVD—assuming all your drives can use it.

DVD-R is a write-once medium similar to CD-R, which was originally created by Pioneer and released by the DVD Forum in July 1997. You can play DVD-R discs on standard DVD-ROM drives. Some 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 preengraved 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 11.14).

Storage capacity

4.7GB single-sided; 9.4GB double-sided

Disc diameter

80mm-120mm

Disc thickness

1.2mm (0.6mm×2: bonded structure)

Recording method

Organic dye layer recording method

Laser wavelength

635nm (recording); 635nm/650nm

 

(playback)

Data bit length

0.293 microns

Recording track pitch

0.80 microns

Track format

Wobbled groove

DVD-R media is currently available in speeds up to 16x, although some drives feature faster burn speeds. Some vendors are now producing double-sided single-layer DVD-R media with capacities of 9.4GB. This media is designed primarily for DVD jukeboxes, although it can be used by standard DVD rewritable drives.

DVD-R DL was introduced in February 2005 and is sometimes known as DVD-R for Dual Layer or DVD-R9. DVD-R DL is essentially a dual-layer version of the DVD-R disc, using the same recording method, laser wavelength, and other specifications. However, DVD-R DL discs have two recording layers, with the reflective surface of the top layer being semi-transparent to permit recording on the second layer. Because of the lower reflectivity of the top layer, some DVD-ROM drives cannot read DVD-R DL media.

Note

If you are unable to read DVD-R DL media with a DVD drive, try using the Layer Jump Recording (LJR) recording method in your DVD mastering software if your drive and software support it. LJR alternates between recording layers during the writing process, rather than filling one layer before writing to the other layer. This permits a disc to support multisession recording and is intended to make it easier for DVD drives to read dual-layer media.

DVD-R DL media is currently available in 4x speed from a relatively small number of suppliers, although some rewritable DVD drives support faster write speeds.

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 drives than DVDRAM. 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.

The most common types of DVD-RW media support 2x speeds, although 4x and 6x media is also available. Drives supporting 2x/4x and faster media have several advantages over original 1x/2x DVDRW 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 and faster drives can use DVDRW media in a few seconds after insertion, formatting the media in the background as necessary. This is similar to the way in which DVD+RW drives work.

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

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

However, most 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.

Note

Plextor’s Zero Link technology does support selective file erasure on DVD-RW media. Essentially, Zero Link provides an equivalent to DVD+RW’s lossless link feature, enabling DVD-Video players that support DVD-RW media to play edited disks.

DVD+RW, also called DVD Phase Change Rewritable, has been the premier DVD recordable standard because it is the least expensive, easiest to use, fastest, 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.dvdservices.org). 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 burning times and easier operation, DVD+RW is the most popular rewritable DVD format.

Table 11.15 lists the basic specifications for DVD+RW drives.

Storage capacity

4.7GB single-sided; 9.4GB double-sided

Disc diameter

120mm

Disc thickness

1.2mm (0.6mm×2: bonded structure)

Recording method

Phase change

Laser wavelength

650nm (recording/playback)

Data bit length

0.4 microns

Recording track pitch

0.74 microns

Track format

Wobbled groove

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.

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 11.14), 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 positioning for lossless linking, but drives made only for DVD+R/RW media can’t write to other types of DVD rewritable or recordable 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 include the following:

■ Single-sided discs (4.7GB).

■ Double-sided discs (9.4GB).

■ Up to 4 hours video recording (single-sided discs).

■ Up to 8 hours video recording (double-sided discs).

■ Bare discs—no caddy required.

■ 650nm laser (same as DVD-Video).

■ Constant linear data density.

■ CLV and CAV recording.

■ Write speeds 1x-4x and higher (depending on the drive).

■ DVD-Video data rates.

■ UDF (Universal Disc Format) file system.

■ Defect management integral to the drive.

■ Quick formatting.

■ Uses same 8-to-16 modulation and error-correcting codes as DVD-ROM.

■ Sequential and random recording.

■ Lossless linking. (Multiple recording sessions don’t waste space.)

■ Spiral groove with radial wobble.

■ After recording, all physical parameters comply with the DVD-ROM specification.

DVD+RW technology is 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+R/RW is the format I prefer and recommend, and it has been the format most users prefer for data recording. However, today’s multiformat drives support both DVD+R/RW and DVD-R/RW (and Super Multi Drives support DVD-RAM), so you can choose the right media for a particular task.

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 three possible solutions:

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

■ Change the Book Type Field during the creation of a disc with a DVD mastering program.

■ Use a compatibility utility to change the contents of the Book Type Field for a particular
DVD+RW disc as necessary. These utilities may be provided by the drive manufacturer (sometimes a firmware upgrade is also necessary) or by a third-party utility.

Changing the Book Type Field is known as bitsetting.

DVD+R DL, also known as DVD-R9, is a dual-layer version of the DVD+R standard that was introduced in October 2003. DVD+R DL is essentially a dual-layer version of the DVD+R disc, using the same recording method, laser wavelength, and other specifications. However, DVD+R DL discs have two recording layers, with the reflective surface of the top layer being semi-transparent to permit recording on the second layer. Because of the lower reflectivity of the top layer, some DVD-ROM drives cannot read DVD+R DL media. DVD+RW DL media is typically rated at 8x recording speeds. Connectors On A Hard Disk Drive Optical Storage Optical storage drives are the most economial and practical way of backing up your computer's vital data. They also remain the easiest way to install new software into a computer. This series of pages will teach you different aspects associated with how optical drives work. Connectors On A Hard Disk Drive On this page: Overview of DVD-RAM Technologies
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