Different Kinds of CD and DVD Formats

The Compact Disc
A Compact Disc or "CD" is an optical disc used to store digital data. Originally designed in 1980 through a joint partnership between Sony and Philips, this media was designed as a successor to the gramophone record. When the design was originally proposed, the partnership team aimed at producing a disc with a playing time of 60 minutes. Sony's vice-president, Norio Oga, suggested setting the capacity to accommodate Wilhelm Furtwängler's recording of Ludwig van Beethoven's Symphony Number Nine from the 1951 Bayreuth Festival. This limit was later extended to 80 minutes.

The medium would eventually be expanded to not only hold data in the form of CD-ROM but also video in the form of Video Compact Discs (VCD) and Super Video Compact Discs (SVCD) as well as photos and other interactive demonstrations. Despite being around for over 20 years, the CD remains the physical standard for audio media.

CD-DA or the Audio CD
This is the term that describes the format for the audio CD, officially known as Compact Disc Digital Audio or CD-DA and was originally designed to replace the gramophone record. It overcame many of the limitations of records and compact cassettes, the two main audio physical standards of the time. Some of the problems overcome included sound quality depending on the record's vinyl quality and degradation of frequency response with each playback.

The standard for the Compact Disc, described in a document known as "Red Book" due to the color of its cover, defines the features and technical characteristics of the medium, among them the use of two-channel 16-bit PCM encoding and the ability to reproduce an audible frequency range of 20Hz to 20kHz. Unlike records or cassette tapes, which can have mono-aural recordings, mono-sourced performances were not described but is usually presented as two identical channels on the stereo tracks.

Four-channel sound, while an option in the Red Book standard, has never been implemented in any commercial recording but this can be seen in the newer DVD audio format. In the early days of the CD, vinyl records were prized by audiophiles as having much better sound quality, a belief that persists today even with the improvements in digital audio technology. The perception may be due in part that early consumer CD players sometimes used 14-bit digital-to-analog converters than the correct 16-bit decoders, a limitation implemented to cut cost that does not exist today. But despite this, the debate continues as to which is the better medium for audio quality.

CD-Text
CD-Text is an extension of the Red Book standard that allows for the storage and display of additional information e.g. song name, album name, artist, etc. While support is common, it is not universal and not all players, software or hardware utilizes this feature. This feature is increasingly being utilized in modern car systems to display audio information. CD+Graphics (CD+G) and CD+ Extended Graphics (CD+EG/CD+XG)

Both formats are special audio CDs that contains graphic data in addition to the audio data already on the disc. These discs can be played on a normal audio CD player but on special player, the graphics can be displayed on a screen or computer monitor. This information is typically used to display lyrics and used in karaoke machines.

Super Audio CD (SACD)
The Super Audio CD is a high-resolution audio disc format that goes further than the CD-DA standard to provide much higher fidelity audio. This format was specifically designed to compete against with DVD-Audio, another high-fidelity audio format but neither format has won over or replaced audio CDs.

SACD has the added feature of being able to produce hybrid discs that not only contain the higher fidelity SACD audio stream but also standard audio CD data. This allows these discs to be played on standard CD players and thus making them backwards compatible.

CD-ROM
The Compact Disc was originally intended to be used purely for audio. In 1985, Sony and Philips would establish the standards for computer data storage using the same physical format as audio Compact Discs. These discs were readable on computers with CD-ROM drive.

Video CD(VCD) and Super Video CD (SVCD)
The VCD and SVCD were the standard format for storing video material on a CD and were playable on dedicated VCD players as well as DVD players.

In the case of VCD, the video quality was comparable to VHS video while SVCD is slightly better.

Photo CD and Picture CD
Both the Photo CD and the Picture CD were file formats designed by Kodak for the storing of photos on a CD. These formats are very different and not to be confused with each other. The Photo CD is designed to hold approximately 100 high quality images while the Picture CD format is a consumer product designed to hold compressed JPEG images.

CD-i
This format is the standard for interactive media. The software and data needed to run and use the discs are stored on the disc's first track and hidden from the disc's table of contents. This makes this information "invisible" to standard audio CD players.

CD-i was a relatively short lived format but saw title that included interactive coloring books and games for children.

Enhanced CD
The Enhanced CD, also known as CD Extra or CD Plus, was used by the recording industry to combine audio and computer data. This allowed special features to be accessed by computers with CD-ROM drives.

These CDs found increased popularity in the late 1990's with increased computer usage. Iron Maiden was one of the first bands to use Enhanced CDs when they released their remastered albums.

Recording to CDs
There are several options when it comes to storing your own personal data onto to CDs. You can either make a permanent copy, in the case of CD-R or you can write to a media that can be erased and re-used, in the case of CD-RW.

CD Recordable (CD-R)
Recordable CDs, or CD-Rs, are made with a photosensitive dye that is injected into the data spiral. The write laser of the CD burner changes the color of the dye allowing it to be read by the read laser of a CD player like it would a standard CD.

CD-R burns are designed to be permanent but studies have shown that the dye's physical characteristics may change over time and eventually render the media unreadable. While the physical media may last as between 20 to 100 years, the longevity of the stored information may not last as long and is dependent on things like disc quality, the quality of the burning drive and storage conditions. Some tests have shown information degradation in as little as 18 month under normal storage conditions; putting them in a drawer as a typical user normally does.

CD Rewritable (CD-RW)
CD-RW are made with a metallic alloy as opposed to the dyes used in CD-R. The write laser in the burner heats the alloy and changes the physical characteristics and hence the reflectivity of the alloy. This allows information to be stored in the same way a normal CD stores information.

DVDs
The Digital Versatile Disc, sometimes known as Digital Video Disc, or DVD, is an optical storage media like the CD. Its main uses are the storage of video and data. While a DVD has the same physical characteristics of a CD, the media is capable of storing far more information. Unlike the CD, which was initially designed only for audio and grew to include many different formats, the DVD has two, DVD Video and DVD Audio.

DVD Video
DVD Video is currently the dominant consumer format for digital video and the one most people are familiar with. First introduced in Japan in 1996, it quickly rose in popularity to eventually replace VHS. It has yet to be replaced by the newer Blu-Ray format, which has surpassed DVDs in popularity only in Japan.

DVD Video encodes the video and audio data as compressed MPEG-2 files which produces video and audio that far surpasses the quality of its VHS predecessor. The format also supports other features such as sub-titles, chapters for ease in navigation and extra features.

DVD Audio
DVD Audio, usually abbreviated as DVD-A, is the format for high-fidelity audio on a DVD disc. This standard is not intended for the delivery of video and has little in common with its video sibling. What it does feature is a wide range of audio options from compressed to uncompressed audio recorded in mono-aural all the way up to 5.1 full surround.

DVD-A was first introduced in 2000 and entered a format war with SACD. Neither format emerged a winner, leaving the audio CD the dominant consumer physical audio format.

Recording to DVD
Like the CD format that came before it, DVDs come with their own recordable formats that allows a user to either write once, as in the case of DVD-R and DVD+R, write multiple times, as in the case of DVD-RW and DVD+RW, or to store data, DVD-RAM.

DVD-R/DVD+R
The DVD-R and DVD+R are both writable standards that while similar to each other in goal are incompatible in the way data is written or read. Like their recordable CD counterparts, they both use a photo-reactive dye to record data. Both formats serve the same purpose, to store either data or video information and while there are some technical differences between the two, the difference is hardly noticeable to the average user as most burners and players today are capable of using both formats.

As of 2007, the market shows no sign of settling for either the plus or the minus standard, so chances are, we will see both on the shelves for a long time to come.

DVD-RW/DVD+RW
These are both rewritable DVD standards that allows a user to erase and rewrite data to the disc. Like their CD-RW counterpart, they also use a crystalline metallic alloy to record data and like their recordable counterparts, there is no clear preference for either in the consumer market as new DVD burners and players can read and write to both formats. It is thus unlikely any one will dominate the other any time soon.

DVD-RAM
This stands for DVD-Random Access Memory and is a rewritable DVD format used primarily in computers for storing and backing up data. As the format has built-in error control and defect management, it is seen as a more reliable format for data storage than any of the writable or rewritable DVD standards. In addition, DVD-RAM also offers better longevity of written data and can be rewritten more times than the standard RW disc. This makes it particularly attractive for data archival purposes.