Distinguishing Major Digital Optical Disc Formats

Distinguishing Some Major Digital Optical Disc Formats

Author: Jim Soe Nyun
Date: March 14, 2006

Scope: Often it is difficult to decide whether a computer disc is a CD-ROM, audio CD, DVD video, or DVD-ROM. Procedures for accompanying materials require you to treat different formats in different ways. Also, when preparing a bibliographic record, it is necessary to accurately describe the format. This document will help you make the distinction between some of the more common formats.

Definitions

CD-Audio: An optical disc containing sound material encoded according to the compact disc digital audio (CDDA) standard. CD-Audio discs will play in audio compact disc players and many standalone DVD players (though of course there will be no images to view). They are also usually playable on a computer equipped with a CD or DVD drive. The occasional CD-Audio discs with secondary extra material such as images or text can have their audio content played on a CD player, though they require a computer with a CD drive to access the secondary content. The latter discs are occasionally referred to as "Enhanced CDs." Even with the enhanced content, their audio content is encoded according to the CCDA standard and they are usually considered CD-Audio discs.

CD- ROM: An optical disc containing information that is meant to be accessed by a computer, not an audio CD player. The information on the disc may take multiple forms: census data, computer programs, text, images, video games, and so forth. The information may even be audio and video, though the main purpose of the disc is usually to present data, and any audio and video content will not be encoded in the CD-Audio or DVD-Video formats. These discs must be inserted into your computer to access their content and will not work in audio CD players. Discs containing MP3 sound files, because the files are not in the special CD-Audio format, are considered CD-ROMs. Exceptionally, some standalone CD players will play CD-ROMs with MP3 files.

DVD-ROM: Similar to CD-ROMs, DVD-ROM discs contain data. They must be inserted into a DVD drive on your computer to access their content and will not play in standalone video DVD players.

DVD-Video: Often referred to as simply "DVD," this format encodes moving image material on a DVD disc. They're playable on standalone DVD players and computers equipped with a DVD drive and software to decode the discs (such as WinDVD). Many of the programs that will play a CD will also play DVD-Videos, including Windows Media Player and RealPlayer.

A common DVD-Video graphic:

Video CD: Often alternately called a VCD, this format is popular in Asia, though rare in the United States . Because of the lower storage capability of the CD disc, the duration of material is necessarily shorter than what would be possible on a DVD. Also, the sound and picture quality are typically of a lower quality. VCDs are playable on some standalone DVD players and on some computers with a CD or DVD drive and certain video decoders. Most of these do not automatically play when inserted into a computer CD drive, though they will likely open Windows Explorer. The root directory will have various folders, including one called "VCD," and another called "MPEGAV." Navigate to the MPEGAV folder, and then click on a file to launch the computer's VCD player.

Some common Video CD Graphics: or

Most examples of optical computer discs are 4 3/4 inches across. CDs and DVDs differ from each other in the amount of data the format can hold on a disc. A single CD can hold about 650 megabytes of information. A DVD has a much higher capacity, with each disc able to hold 4.7 gigabytes of data. However, it is virtually impossible to distinguish the different presentation formats by simply looking at them.

The easiest way to decide what kind of disc you have is to look at the disc or the accompanying packaging or material. Often they will identify the discs as to what type of media they are. Catalog records for the material can also be a good source of information, though that information is occasionally inaccurate.

Failing that, insert the disc in your computer. If a computer program on the disc launches, or if Windows Explorer opens showing you the files contained on the disc, consider the disc a data disc (CD-ROM or DVD-ROM) in most cases. (VCDs would be the primary exception in that they often don't launch a media player.) If an audio media program opens (such as Windows Media Player, RealPlayer or LiquidAudio) and starts to play sound on the disc, it is CD-Audio. If a media program opens and starts to play video content, with or without sound, consider the disc DVD-Video.

Below is a table of the above formats and ways you can distinguish between them.

Identifying Characteristics	CD-Audio	CD-ROM	DVD-ROM	DVD-Video	VCD
Item, container or accompanying material calls disc CD-Audio.	Many discs	No	No	No	No
Item, container or accompanying material calls disc a CD.	Some discs	Some discs	No	No	Almost never
Item, container or accompanying material calls disc DVD-Video.	No	No	No	Many discs	No
Item, container or accompanying material calls disc a DVD.	No	No	Some discs	Some discs	No
Item, container or accompanying material calls disc Video CD or VCD.	No	No	No	No	Many discs
Plays on standalone audio CD player.	YES	Only MP3 files on a CD-ROM on a player designed to play them	No	No	No
Plays on standalone DVD player.	Some players, audio only	No	No	YES	Some discs, on some players
Computer with CD (not DVD) drive can access a disc. If you lack the proper player for the files you may not be able to play the media on the disc; but you will be able to view the files using Windows Explorer.	YES	YES	No	No	YES
Inserting in computer CD or DVD drive will usually launch a media player that will play audio through headphones or speakers attached to the computer.	YES	No	No	No	No
Inserting in computer CD (not DVD) drive will often open some sort of computer program contained on the disc.	Some discs, Enhanced CDs only	YES	No	No	No
Inserting in computer DVD (not just CD) drive will often open some sort of computer program contained on the disc.	Some discs, Enhanced CDs only	YES	YES	Some discs with enhanced content	No
Contents can be accessed on computer with DVD drive. If you lack the proper player for the files you may not be able to play the media on the disc; but you will be able to view the files using Windows Explorer.	YES	YES	YES	YES	YES
Inserting in computer DVD drive will often launch a media player that will play video content.	No	No	No	YES	Rarely
When using Windows Explorer to view the contents of the disc, the disc will have a directory called "VCD."	No	No	No	No	YES
Item is a custom-burned disc (as opposed to commercially pressed) and the data side is green in color.	Some discs	Some discs	No	No	Some discs
Item is a custom-burned disc (as opposed to commercially pressed) and the data side is blue-violet in color.	No	No	Some discs	Some discs	No