This International Standard specifies the mechanical, physical and optical characteristics of a 120 mm, read-only optical disk to enable the interchange of such disks. It specifies the quality of the recorded signals, the format of the data and the recording method, thereby allowing for information interchange by means of such disks. This disk is identified as DVD - Read-Only Disk. This International Standard specifies − four related but different Types of this disk (see clause 7), − the conditions for conformance, − the environments in which the disk is to be operated and stored, − the mechanical and physical characteristics of the disk, so as to provide mechanical interchange between data processing systems, − the format of the information on the disk, including the physical disposition of the tracks and sectors, the error correcting codes and the coding method used, − the characteristics of the signals recorded on the disk, enabling data processing systems to read the data from the disk. This International Standard provides for interchange of disks between disk drives. Together with a standard for volume and file structure, it provides for full data interchange between data processing systems.