This International Standard defines a series of related 130 mm optical disk cartridges (ODCs) by using a number of Type designations. A disk has two sides, called Side A and Side B. Each side can have a nominal capacity of 1,3 Gbytes. Type R/W provides for data to be written, read and erased many times over the recording surface of the corresponding disk side, using thermo-magnetic and magneto-optical effects. Type P-ROM provides for a part of the disk surface to be pre-recorded and reproduced by stamping or other means. This part of the disk is read without recourse to the magneto-optical effect. All parts which are not pre-recorded provide for data to meet the requirements of Type R/W. Type O-ROM provides for the whole of the disk surface to be pre-recorded and reproduced by stamping or other means. The corresponding disk sides are read without recourse to the magneto-optical effect. Type DOW provides for data to be written and read many times over the recording surface of the corresponding disk side, using the direct overwrite thermo-magnetic and magneto-optical effects requiring a single external magnetic field. Type P-DOW provides for a part of the disk surface to be pre-recorded and reproduced by stamping or other means. This part of the disk is read without recourse to the magneto-optical effect. All parts which are not pre-recorded provide for data to meet the requirements of Type DOW. Type WO provides write once, read multiple functionality using the thermo-magnetic and magneto-optical effects. Type WO-DOW provides write once, read multiple functionality using the direct overwrite thermo-magnetic and magnetooptical effects. In addition, for each Type, this International Standard provides for cartridges with a sector size of 512 bytes and cartridges with a sector size of 1 024 bytes. All sectors of a disk are the same size. This International Standard specifies — the conditions for conformance testing and the Reference Drive; — the environments in which the cartridges are to be operated and stored; — the mechanical, physical and dimensional characteristics of the cartridge, so as to provide mechanical interchangeability between data processing systems; — the format of the information on the disk, both embossed and user—written, including the physical disposition of the tracks and sectors, the error correction codes, the modulation methods used; — the characteristics of the embossed information on the disk; — the magneto—optical characteristics of the disk, enabling processing systems to writedata onto the disk; — the minimum quality of user—written data on the disk, enabling data processing systems to read data from the disk. This International Standard provides for interchange between optical disk drives. Together with a Standard for volume and file structure it provides for full data interchange between data processing systems.