The Different Types of Optical Disc
CD-ROM is just one type of compact disc format. Each format is a different way to organize the data stored on the disc. The format allows the disc to be used for a specific purpose. For a CD drive to play a CD created using a particular format, it must be compatible with that format. Compact disc formats are categorized by book color.
| Book Color | General Purpose | Specific Standard(s) |
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Audio CDs | CD-DA--A typical audio CD |
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Data CDs (CD-ROM generally refers to a data CD created using a Yellow book standard. Several specific standards exist.) | CD-ROM--The original data CD standard. Several variations of the original data CD-ROM standard exist, but they are largely specific to particular operating systems. ISO 9660--A more standardized format than the original CD-ROM standard. Unlike other standards based on the original CD-ROM standard, this standard is not operating system-specific. The predecessor to the ISO 9660 standard was called the High Sierra format. CD-ROM XA--An extension to the ISO 9660 standard. Allows multiple types of data (audio, data, video) to be put on the same CD. |
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Interactive CDs | CD-I--A proprietary standard for creating CDs with built-in interactivity. These are not CDs with interactive software programs on them. |
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Video CDs | Video CD--A standard for structuring digitized MPEG video files. |
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Multi-session CDs (Defines standards for recording data to a CD in more than one increment.) | CD-R--The standard for recordable optical CDs. CD-RW--The standard for re-writeable optical CDs. |
Note: A typical data CD-ROM disc holds approximately 650 MB of data.
DVD (Digital Video Disc or Digital Versatile Disc) is an optical media standard that can be used to store large amounts of different types of data (computer data, video, audio).
Recordable DVDs use two different formats for recording data: DVD-R/RW and DVD+R/RW.
- DVD+R is a variation of DVD-R and is generally considered more robust.
- Most DVD drives can read and write either format. Older drives or older DVD players might only support DVD-R.
Unlike CDs, which contain data only on a single side, DVDs can contain data on both sides of the disc.
- A DVD with a single side of data can hold about 4.7 GB.
- A double sided disc can hold about 9.4 GB.
Some DVDs can store data in two different layers on the same side.
- The outer layer is semi-transparent, allowing the laser to read data from the inner layer.
- Dual layer discs can hold up to 8.5 GB of data.
- Double sided, dual layer disc are possible (but rare), and can hold up to 17 GB.
- Most newer drives can read both single and dual layer discs. Older drives might not support dual layer discs, and dual layer recordable discs cost more than single layer discs.
DVD speeds use a multiple of 1.35 MBps (1x = 1.35 MBps, 2x = 2.7 MBps, etc.).
Blu-ray Disc (BD) is a new optical disc format that is capable of greater storage capacity than DVDs. Blu-ray was originally developed for high definition video (and expanded content on movie discs), but can also be used for data storage.
Blu-ray uses a blue laser instead of the red laser used with CDs and DVDs. The blue laser light has a shorter wavelength, which allows data to be packed more tightly on the disc. A single layer Blu-ray disc holds 25 GB; a double layer disc holds up to 50 GB. Experimental 20 layer discs can hold up to 500 GB.
Blu-ray discs can be read-only (BD-ROM), recordable (BD-R), or rewritable (BD-RE).
A 1x Blu-ray drive reads data at 4.5 MBps. For HD video, the minimum playback requires 2x speeds. Most Blu-ray drives include a second read laser for reading CDs and DVDs. Without this additional laser, Blu-ray drives would not be able to read CDs or DVDs. Blu-ray is intended to eventually replace DVD.
A competing standard, HD DVD, was used by many movie distributors. Blu-ray has become the accepted HD video standard as the last movie studio stopped distributing HD DVD movies.