Specifications
The smallest entity in the CD format is called a frame, and holds 24 bytes. Data in a CD-ROM is organized in frames and sectors. A CD-ROM sector contains 98 frames, and holds 2352 bytes.
CD-ROM Mode 1, usually used for computer data, divides the 2352 byte data area defined by the Red Book standards into 12 bytes of synchronization information, 4 bytes of header data, 2048 bytes of user data and 288 bytes of error correction and detection codes. These codes help prevent the data from becoming corrupted after readout. Executable data is particularly error intolerant and read errors would lead to arbitrary results.
CD-ROM Mode 2 Form 1, usually used for computer data, has the same user data and error correction as Mode 1, but with a slightly different layout. Although its use is not recommended for compatibility reasons, nevertheless much premastered material is produced in the format.
CD-ROM Mode 2 Form 2, intended to be used for error-tolerant data such as audio and video, divides the 2352 bytes into 12 bytes of synchronization information, 4 bytes of header data and 2336 bytes of user data. Mode 2 provides 14% more user data space than Mode 1 by omitting error correction, since a read error in audio or video will only cause a small flaw which may not even be detectable by humans. Video CDs are classified as Mode 2 Form 2.
Most DVD/CD disc authoring software will allow a DVD to be written in one, some or all of the above modes. Any DVD drive will read single layer discs as the drive software just regards the disc as a very large CD. However, dual layer discs are more problematic. Some drives will simply regard them as an even larger CD, but many models, recognising that there are no dual layer CDs, only permitted access to the first layer. Some Blu-ray burning software will also allow Blu-ray discs to be produced in one or more of the above formats. The limitations of CDFS are likely to manifest themselves on such a large medium.
Read more about this topic: ISO 9660