The formats of CD-ROMs are defined by several standards. The first is a proprietary standard known as the “Red Book” (formerly CD-DA), which defines those features that are common to CD-Audio and CD-ROM. It includes a measure of error correction that is adequate for audio disks. The second standard, the international standard ISO 10149, defines the additional features (including more powerful error correction) needed to allow data to be held on the disk, i.e. for recording on CD-ROM; it supersedes the proprietary “Yellow Book” standard. The third standard, ISO 9660 (developed from the earlier High Sierra standard), defines how a data file is represented on the disk in such a way that it can be accessed by different operating systems. A commonly supported extension to ISO 9660, Joliet, allows less restrictive filenames.
The CD-R format is regulated by the proprietary standard known as the “Orange Book”. This defines a recordable (write-once) disk that is closely compatible with CD-ROM; systems that can read CD-ROM disks can also read the CD-R format. The later CD-RW format allowed disks to be erased and reused.
A less frequently used format standard is CD+G, which allows an audio CD to carry a few graphic images; it is intended for consumer products rather than computers.
As the Red Book standard is common to all CD disks, most CD-ROM drives can play standard audio CD disks on which sound is recorded in the simple Red Book format and not interleaved with data or images.