This International Standard specifies the characteristics of 90 mm Optical Disk Cartridges (ODCs) using the Phase Change technology, with a capacity of 1,3 Gbytes per cartridge. It specifies three related Types of such cartridges. Type R/W Provides for data to be written or overwritten and read many times over the recording surface of the disk using the Phase Change overwritable effect. Type P-ROM Provides for a part of the recording surfaces of the disk to be embossed by stamping or other means. This part of the disk is read without recourse to the Phase Change overwritable effect. All Parts which are not embossed provide for data to meet the requirements of Type R/W. Type O-ROM Provides for the whole of the recording surfaces of the disk to be embossed and reproduced by stamping or other means. This type of disk is read without recourse to the Phase Change overwritable effect. For each Type, this International Standard provides for 5 12-byte and 2 04%byte sectors. All sectors of a given cartridge have the Same size. Type R/W, Type P-ROM and Type O-ROM are also referred to as “fully overwritable”, “partially embossed” and “fully embossed”, respectively. This International Standard specifies - the conditions for conformance testing and the Reference Drive; - the environments in which the cartridges are to be operated, stored and transported; - the mechanical and physical 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, and the modulation method used; - the characteristics of the embossed information on the disk; - the Phase Change overwritable characteristics of the disk, enabling processing Systems to overwrite data 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.