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The Confusing World of DVD Media

A Guide to the Various DVD Recording Formats

Being able to record DVDs on a personal computer has its advantages.

DVD media can hold over seven times the information of a standard compact disc. Also, consumers want to produce and burn their own video creations and have them work with most set-top DVD players. As recording hardware and blank media prices continue to fall, more and more people will consider adding this technology to their PC's arsenal.

Consumers shopping for a new DVD recorder should first ask themselves two questions. First, what level of compatibility are you looking for? Second, what DVD-recordable format would best suit the task?

The answer to the first question is usually an easy one. You want a media format that will be readable by another computer or will play in a majority of set-top DVD players.

The second question is arguably the most confusing. For consumers, there are two main types of recordable DVDs available.

Unfortunately, the similar naming conventions and near identical features of these competing formats do little but confuse the average person.

DVD Basics

DVDs are externally identical to the CD. Both are 120mm in diameter and 1.2mm thick. DVDs can be single or double sided, and each side may contain a second layer that further extends the storage capacity of the disc. Current DVD standards have settled on a format allowing up to 4.7 gigabytes of data storage per side (single layer).

Recordable DVDs match this storage size, but differ in terms of how they go about achieving it. The two forms of recordable DVD media currently available are called DVD+RW (DVD "plus" RW) and DVD-RW (DVD "dash" RW). There is another recordable format called DVD-RAM that first appeared in the late '90s, but its general lack of compatibility with set-top players has made it an unpopular medium for all but its most diehard supporters.

DVD recording speed terminology differs significantly from CD speed ratings. A CD recorder burning at 1x is recording data at .15 MB/s. DVDs also use an "x" speed rating with 1x being equal to 1.39 MB/s. Consumer DVD recording technology is currently limited to 8x recording (11.08 MB/s) for DVD-R and +R formats. DVD-RW and +RW formats have reached 4x recording speeds. DVD recording speeds expressed in terms of the more familiar CD recording speeds would roughly equate to 9x for 1x DVD recording, 18x for 2x recording, and 22x for 2.4x recording. At 8x DVD recording speeds, a 4.7GB disc takes about 8 minutes to fill.

All recordable DVD media types feature a microscopic wobbled groove embedded in the plastic substrate. This wobble provides the recorder with the timing information needed to place data accurately on the disc. Pressed DVDs, as the prerecorded movies you can buy or rent, are not recordable and do not have or require the wobbled groove found on blank media. Pressed DVDs have a smooth groove, so to speak.

All consumer DVD recordable technologies mentioned in this article contain form(s) of copy protection to prevent the unauthorized duplication of copyrighted material. Don't purchase a DVD recorder and expect to create bit-for-bit copies of The Matrix or any copy-protected DVD to share with all of your friends. Besides the legal issues, it simply won't work.

DVD-RAM Explained

If you have never heard of DVD-RAM, you probably have no use for it and can skip ahead to the next two recordable formats. DVD-RAM is only available in rewritable formats. Discs can be rewritten up to 100,000 times. If you are looking to burn a disc that cannot be altered later on, DVD-RAM is not for you.

DVD-RAM discs are easily identified by the pre-embossed sector headers that form a visible pattern on the data side of the disc. Originally, DVD-RAM media was encased in sealed cartridges designed to protect the discs from scratches and fingerprints. Today, the cartridges are optional (or removable) as not all drives that support the DVD-RAM format require them. Of all rewritable types of DVD media, DVD-RAM is the least compatible with set-top DVD players and older DVD-ROM drives.

DVD-RAM differs from other DVD recording technologies in that it's the only one designed to act as random access memory, the "RAM" part of DVD-RAM. This random access system gives DVD-RAM an advantage over other DVD recordable formats by allowing it to quickly find and retrieve data anywhere on the disc. DVD-RAM drives make good removable storage systems, as drag-and-drop recording is usually driver supported from within the operating system.

DVD-RAM includes a good defect-management system. Physical errors on the disc are handled automatically and provide an error-free environment necessary for long-term use.

A Look at ‘Dash’

Pioneer developed the DVD-RW format to give consumers a medium to record DVDs for home use. DVD-RW was the first consumer format to offer compatibility with a majority of set-top DVD players. Introduced initially as a write-once technology (DVD-R), Pioneer quickly added a rewritable media type, and thus DVD-RW was born.

DVD-RW features a linear data format that packs information into a single continuous stream similar to the CD-RW technology it is partially based upon. DVD-RW lacks the native defect management and random file access of DVD-RAM, but its broad compatibility and relatively inexpensive media make DVD-R/-RW the best choice for most consumers.

DVD-RW (rewritable) makes use of phase-changing materials similar to those found in CD-RW media, and is currently limited to 4x recording speeds. Recording performance for DVD-R (write-once) tops out at 8x.

You will often see blank DVD-RW media (-R or -RW) listed with a "(G)" attached to the end. DVD-RW comes in two media types — Authoring (A) and General Use (G). DVD-RW for Authoring requires expensive recording equipment and is intended for professional use. The rest of us will stick to using General Use media as both the recorders and blank media are far less expensive.

Compared to DVD-RAM's 100,000 rewrite rating, DVD-RW is rated for up to 1,000 rewrites.

The ‘Plus’ Side

Developed by the DVD+RW Alliance that includes Sony, HP, Philips Electronics, and Yamaha, DVD+RW is a format that shares many characteristics with DVD-RW. Both types of blank media hold the same amount of data and are available in write-once (-R/+R) and rewritable (-RW/+RW) formats.

Currently the fastest of all DVD recordable formats, DVD+RW/+R offers recording speeds that are about 5 percent faster than DVD-RW.

Initially, DVD+RW was dubbed "the compatible, rewritable DVD format." However, as with all rewritable media formats, the less-reflective nature of rewritable DVDs cannot match the set-top compatibility of write-once blank media. For this very reason, the DVD+RW Alliance quickly introduced the +R format to improve its compatibility.

Be aware that the first-generation DVD+RW drives supported only DVD+RW and not DVD+R. These first-generation products cannot be updated and we recommend avoiding them.

Using phase-change media similar to CD-RW technology, DVD+RW can be formatted for sequential data streams (video) or random access similar to capabilities of the cartridge-based DVD-RAM technology. Compared to DVD-RW, DVD+RW incorporates a higher frequency wobble in its embedded microscopic tracking groove.

Proponents claim that DVD+RW's increased wobble frequency will provide more accurate timing information and thus DVDs that are even more compatible with older set-top players. In reality, increased compatibility comes from using the more reflective write-once media.

While DVD+RW/R offers impressive recording speeds, bulk blank media prices are significantly higher than DVD-RW/R and are available from far fewer vendors. Until DVD+RW/R disc manufacturing levels increase significantly, DVD-RW/R will continue to offer better pricing and availability.

Posted by thinkum at April 3, 2004 10:27 AM