CD-ROM format standards

CD-ROM format standards The formats of CD-ROMs are defined by standards. They can be divided into two groups: firstly the basic standards, now followed by nearly every CD-ROM disk, which define how data files are recorded on disk regardless of what kind of data is contained in the files; secondly, more specialized standards for the handling of data of various types, such as sound, image, or text, or a mixture of these (multimedia). The standards in the first group are intended to apply to all hardware and software configurations that handle CD-ROM disks. The remaining standards may need more specific configurations.

There are three standards in the first group. 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.

The second group of format standards is more diverse. An important subgroup, including DVI (digital video interactive) and CDTV, is concerned with providing TV-quality video (i.e. moving images). Because of the low data transfer rate of CD-ROM drives, this involves powerful data compression, which can also be used for still images; however, video and still bitmapped images do not normally require the additional error correction that is needed for digital data.

The CD-I format is defined by the proprietary standard known as the “Green Book”. This sets down a method of interleaving text, sound, images, and a limited form of video on the same CD-ROM disk, but is aimed at interactive domestic CD players rather than computers. The Green Book defines not only the disk format but also the hardware to support it. CD-ROM XA is a standard similar to CD-I but is aimed at personal computers.

The CD-R and CD-RW formats are 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. Systems designed to read recordable disks must be multisession compatible if the disk is written in several separate sessions rather than recorded in one session (i.e. at one time, with a single table of contents); most modern systems (and all that support CD-ROM XA) comply. Photo-CD is a proprietary format for the recording of scanned color photographs on CD-R disks.

Two less frequently used format standards are CD-V, which allows a suitable player to read both CD-ROM and videodisk, and CD+G, which allows an audio CD to carry a few graphic images; both are intended for consumer products rather than computers. Other formats are likely to emerge in the future.

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.