Optical Storage Types: DVD
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DVD, which stands for "Digital Video Disc" or "Digital Versatile Disc", may easily be mistaken for an ordinary compact disc (see our previous articles on CD/CD-ROM and CD-R/CD-RW), but it is the amount of data that can be stored in it (4.7 gigabytes), as well as technology that makes this possible, that sets it apart.
Basics, Background, and History
The beginnings of the DVD format may be traced back to the 1990s, where two optical storage formats were in the works. Philips and Sony had the MultiMedia Compact Disc (MMCD), while numerous companies including Toshiba, Time-Warner, Matsushita Electric, Mitsubishi Electric, Pioneer, Thomson, and JVC supported the Super Density Disc (SDD). However, then-president of IBM Lou Gerstner moved for a single standard and a unification of two camps to avoid the mishap once brought by the VHS versus Betamax war. The MMCD was thus abandoned and the SD format took on a number of revisions. In 1995, the DVD specification Version 1.5 was announced. By 1997, the DVD Forum replaced the DVD Consortium and was opened to all companies.
As of today there is no official meaning behind the letters DVD. The term "Digital Versatile Disc" came first, as the primary purpose of the DVD was to fully realize a higher-quality home theater experience. Some members of the DVD Forum, however, believe "Digital Versatile Disc" is more appropriate to denote all-around use and not just video.
Since DVDs can hold an especially large amount of space (several gigabytes, depending on the density you’re buying), these optical discs were unmistakably built for the a heightened home movie experience. DVDs can hold around two hours of high-quality digital video (using MPEG-2 compression), plus digital audio, usually using Dolby Digital or Digital Theater Systems (DTS), not to mention an analog 2-channel stereo. Other features such as subtitles (available in a variety of languages including English), scene selections, and other goodies a movie outfit would like to include. One highlight of watching movies in DVDs is the ability to display them in true widescreen format (look for DVDs that say so). The Pan and Scan option lets you crop your viewing frame to fit your ordinary, non-widescreen box.
Ever since the Sony PlayStation 2 was released in 2000, DVDs have also made their way into video game consoles; the Microsoft Xbox and the Nintendo GameCube and Nintendo Wii has made way for playing DVDs in their consoles through some add-ons while the PlayStation 3 and Xbox 360 don't need any.
Creating and Reading DVDs
DVDs are produced using the same concept of pits and lands appplied to compact discs. The important difference incorporated into DVDs are mentioned below:
- More compact packing of the pits/holes: 1.6 microns in between for CDs, 0.74 microns for DVDs.
- Smaller pits: 0.8 microns for CDs, 0.4 microns for DVDs.
- Use of a red laser at a smaller wavelength: 0.78 microns for CDs, 0.65 microns for DVDs.
Single layer discs can hold 4.7 gigabytes worth of data. Other DVD formats include: single-sided, dual-layer (8.5 GB); double-sided, single-layer (9.4 GB); double-sided, dual-layer (17 GB).
Double-sided DVDs consist of two 0.6-millimeter single-sided discs glued back-to-back. Single-sided DVDs, on the other hand, are glued to a blank disc of the same size to keep the thicknesses standard for all types of DVDs. Dual-layered discs have the outer layer semi-transparent. When reading the disc, the laser starts at the bottom layer then goes to the top layer. Dual-layer discs have silver-colored surfaces whereas single-layer discs have gold surfaces.
DVD Types
DVD-Video
Released in 1996 by the DVD Forum, DVD-V is used primarily for commercial movies, prerecorded on these discs. It is the most common form of DVD you purchase and use. They are interactive and contain features than enhance your movie-viewing experience. Another characteristic of DVD-Video is its support for copy-protective measures, such as Regional Protection and CSS (content scrambling system). Such measures were implemented to prevent piracy.
DVD-Data
Simply put, DVD-Data is your typical DVD containing not video, but other types of digital data.
DVD-Audio
Because of its much higher capacity, DVDs can make space for much higher audio quality. However, audio on DVD has never really caught up with audio CDs because people don’t need extremely high-quality music, as they are content even with compressed MP3 formats.
DVD-R
DVD-Recordables, or DVD-Rs, or DVD-dash-Rs, are the first and most popular formats of recordable DVDs. There are two types: DVD-R Authoring or DVD-R (A) are highly expensive and uncommon discs used for professional needs, as they allow recording of any data; DVD-R General or DVD-R (G) are more available to consumers, but do not allow copying of protected DVDs.
DVD-RW
Just like the dual-state CD-RWs, DVD-Rewritable discs change state under a laser for it to be rewritten on. Specifications require that DVD-RWs should reach up to 1000 instances of these rewritings. One drawback of these discs is that because they have relatively lower reflectivity and are consequently mistaken as dual-layer DVDs, rewritable DVDs are compatible with only around 70% of the players out there.
DVD+R and DVD+RW
The DVD+R and DVD+RW (plus-Rs or plus-RWs) formats are basically competing formats to their "dash-R" or "minus-R" counterparts, but with some noteworthy differences. DVD+RWs provide for: lossless linking (no need to re-record a whole disc if only part of its needs updating), better error handling, EasyWrite or Mt. Rainier technology (transforming the disc into an ordinary floppy or hard drive), twice the maximum writing speed of DVD-RWs. DVD+R and DVD+RW copy protection is called VCPS, or Video Content Protection System for DVD+R/+RW.
DVD-RAM
The DVD-RAM format was developed by Panasonic according to the specifications of the DVD, but logically works like a hard disk.
DVD-VR and DVD+VR
Like most DVD discs, DVD-VRs and DVD+VRs (DVD Video Recording discs) were made for videos. This is taken a step further, though, as these Video Recording formats allow you to create videos on these discs so that they can be edited fully. Features such as adding new video content, changing menu backgrounds, inserting chapters, splitting clips, or removing unwanted scenes are now possible with the DVD VRs. But this also added compatibility issues: support for VR editing may only be found in specialized or high-end hardware and software as of now. As for the "minus" versus "plus" formats, the same rule of thumb regarding incompatibility applies: DVD-VRs are not usually playable in ordinary DVD players and must be used in DVD-VR compatible devices. The same goes for DVD+VRs.
Next: Blu-Ray
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