DVD Standards

There is a standards war going strong in the recordable DVD market, and if you buy a DVD burner, then you get to choose sides. Even if you buy a burner that supports more than one standard, you'll eventually have to pick one type of recordable disc or another to back your data up on.

Backup Critic's goal is not to make you an expert in the detailed technology of DVDs, but to point out the technical facts that may actually affect how you use them, and give you opinions about more subjective areas.

There are a lot of different DVD acronyms and media types, but for the purposes of backing up data, there are really only three groups of recordable DVD standards that you need to know about:

• DVD-RAM
• the "plus" formats (DVD+R, DVD+RW)
• the "dash" formats (DVD-R, DVD-RW)

How the Standards Began

The recordable CD (CD-R) went into production in 1989, and by the end of the 1990's, there was plenty of interest in creating a higher-capacity replacement for recordable CD technology. As usual, there was tension between the desire of individual companies to own the technology, and the desire to cooperate on a single specification to avoid a standards war.

In the end, a group of 10 companies (eventually known as DVD Forum) agreed on two specifications in 1997: DVD-RAM and DVD-R. DVD-R is a write-once specification using dye technology similar to that in recordable CDs (CD-R). Just as CD-Rs could often be played back by normal consumer audio CD players, DVD-R was intended to be compatible enough for most normal consumer video DVD players to use -- consumers would be able to burn a home movie onto a DVD-R, and then play it back on their TV with their video DVD player.

DVD-RAM specified a phase-change technology similar to that in rewritable CDs (CD-RWs). DVD-RAM discs would not be playable in normal consumer video DVD players, but they would let computer users treat the discs like other random access storage systems, copying files, deleting files, and performing other normal filesystem operations at will. In contrast, DVD-R discs were basically designed to be burned all in one continuous burn, from start to finish (no adding more files later, even if there's plenty of space left).

DVD-R versus DVD-RAM

DVD-RAM

"RAM" is the acronym traditionally used for "Random Access Memory". DVD-RAM is a re-writable DVD format; it's obviously not a type of memory, but the implication is clear -- DVD-RAM is a format optimized for random access. Why is that even an issue? Because other DVD formats designed more for movies or music generally focus on being able to pull the data (video and/or audio) off the disk sequentially, and at the constant rate that audio/visual playback demands.

Music and video data is also generally less vulnerable to errors; a few lost bits on the disk might make a tiny glitch in the audio or video, but probably would not render the entire disk unusable. But when you want the DVD to contain a bunch of directories and files, more error correction is required to have confidence that a small set of errors can't result in making entire directories unreadable.

People burning video and audio to DVD are often concerned with speed -- they don't want to burning a one-hour video to require an hour. But people backing up their data are more willing to sacrifice speed for quality, so DVD-RAM drives typically have write verification (which significantly slows writes) enabled by default.

All this is by way of saying that:

DVD-RAM is the DVD standard technically best suited for Windows backups.

Of course, other factors go into choosing a DVD burner, such as cost, compatibility, and so on. As you will see in the pages that follow, non-technical factors may still make you choose one of the other DVD standards for backing up your data.

DVD-R, DVD-RW

As already mentioned, DVD Forum agreed on their common specification for DVD-R, in addition to DVD-RAM. With a DVD-R burner and the right software, you could use your PC to burn a movie onto a disc that then had a fair chance (but not 100%) of being playable in a normal consumer video DVD player.

Did the twin standards of DVD-R and DVD-RAM cover what consumers needed? One obvious gap remaining was the need for a rewritable DVD that could play in consumer video DVD players. DVD-RAM made choices in favor of robustness and faster random access that made DVD-RAM discs incompatible with consumer video DVD players.

Enter the DVD-RW standard. In the year after DVD-RAM burners first shipped, Pioneer shipped their first DVD-RW burner. Using techonology related to that in rewritable CDs (CD-RW), DVD-RW dics could be rewritten many times, and could play correctly in many consumer video DVD players (but not as high a percentage of them as DVD-R). DVD-RW burners can burn DVD-RW, DVD-R, CD-R, and CD-RW discs. They typically cannot read or burn DVD-RAM discs.

By 2003, home movies provided additional demand for DVD-RW. The cost of an individual DVD-R disc took quite a while to fall below $5, and there were the usual problems with new technology. Thus. bleeding-edge adopters might require several tries to burn a movie whose disc had no defects, whose format had no logical errors to keep DVD playback software from working correctly, whose images stayed within the often-clipped screen size of TVs, and so on.

When each tweak to a home movie requires another $5 DVD-R disc, the costs can quickly get ridiculous. DVD-RW let you use one disc over and over until the resulting movie worked correctly and looked right, and then burn a single, final DVD-R disc.

DVD+R and DVD+RW

It was no mean feat to get 10 companies, many vigorous competitors, to agree on a set of standards for DVD formats. In the end, however, the coalition did not quite hold together.

Even as the first drives to support DVD Forum standards started shipping, some members were independently creating their own incompatible specifications to compete with DVD-R and DVD-RW. They named their substitutes, brilliantly enough, DVD+R and DVD+RW (or, collectively, DVD+R/W).

What do you say when your fellow coalition members discover you're working on competing standards that may undermine everyone's hard work? The DVD+R/W standards were pitched as improvements over DVD-R/W that would make them more appealing for random-access data (DVD-RAM was not exactly setting the world on fire, anyway), but not hurt the potentially lucrative video market that DVD-R/W was aimed at.

In actual fact, DVD+R/W failed to deliver on much of its promise for random access, and instead ended up competing directly with DVD-R/W for the video market. For example, the original DVD+RW standard was to be rewritable up to 100,000 times -- 100 times better than DVD-R -- but the version of DVD+RW that actually shipped only promised 1,000 rewrites.

As another example, the DVD+RW standard defined both a constant angular velocity format (CAV) for faster random access, and a constant linear velocity (CLV) format for sequential video playback -- but none of the DVD+RW burners you can buy today support the CAV format.

Plus Versus Dash

As of 2003, DVD-RAM is rarely mentioned, and most talk of DVD standards is about the battle between DVD-R/W and DVD+R/W. In Backup Critic's opinion, the technical differences between these two sets of standards is not particularly compelling. With the advent of affordable burners that support both "plus" and "dash" formats, there's little reason to avoid DVD burners because of fear of choosing the wrong standard.

Ironically, the very maneuvering for competitive advantage that sparked this standards war has turned DVD burners into a commodity -- the very fate that the DVD Forum hoped to avoid by creating (and controlling) a single standard. Prices for DVD burners have plummetted, along with DVD disc prices, leaving thinner profit margins for manufacturers.

In a fascinating case of repetitive history, DVD Forum has been working on higher-capacity standards to succeed DVD-R/W. Once again, however, some members of DVD Forum have elected to also create a competing standard. If the result is once again affordable burners that have to support both standards, then consumers should welcome this particular standards war.

Other DVD Standards

As promised, you really only need to learn about the three sets of DVD standards (DVD-RAM, DVD-R/W, and DVD+R/W) to make good decisions about backing up your data onto DVD. However, there are a couple of other DVD acronyms you might run into and wonder about, so the rest of this page outlines the most popular of them.

Video DVDs

The DVDs that you buy or rent movies on to play on your home DVD player do not belong to any of these recordable DVD standards. These DVDs are more precisely described as "DVD Video".

The CD-ROMs sold in music stores are manufactured by a different process than is used in recordable (CD-R and CD-RW) CDs for PCs -- they even appear different when you look at the recording surface. The situation is entirely analogous for Video DVDs -- they are recorded via a mastering process that is not cost-effective for just making a handful of copies; it's a process quite different than that used in the recordable DVD formats discussed above.

The term "Video DVD" is actually a specification for how the various parts of the video DVD (audio, video, titles, etc.) are logically divided into files. A lower-level standard defines the physical format of the DVD and how a logical filesystem is imposed on that format. That physical standard is called DVD-ROM.

DVD-ROM

The DVDs you rent movies on look different than the DVDs your PC can record on. As mentioned, the physical standard these DVDs use is called DVD-ROM, and it requires a somewhat expensive mastering process.

If you've started to burn movies onto recordable DVDs, you may have discovered that they only hold about 2 hours worth of video, but some Video DVDs can hold nearly 4 hours. That's because the DVD-ROM format supports a wonderful trick not (yet) available in any of the recordable formats discussed here: dual layers. In all cases, the spiral of data on the DVD disc can hold about 4.7GB of data. But it is possible to lay a second layer of data on top of the first, and make it translucent enough for the read head to selectively access either the top layer or the layer beneath it. That results in twice the storage capacity: about 9.4GB.

Except for some DVD-RAM drives, virtually all DVD drives can read DVD-ROM discs.

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