This International Standard specifies the physical and magnetic characteristics of 12,7 mm wide, 36-track magnetic tape cartridges to enable interchangeability of such cartridges. It also specifies the quality of the recorded signals, the format and the recording method, thus allowing, together with International Standard ISO 1001 or equivalent, full data interchange by means of such magnetic tape cartridges. This International Standard specifies two types of cartridge which, for the purposes of this International Standard, are referred to as Cartridge System Tape (CST) and Extended Capacity Cartridge System Tape (ECCST), and contain tape of different thicknesses and lengths. CST cartridges have a nominal uncompressed capacity of approximately 400 Mbytes. ECCST cartridges have a nominal uncompressed capacity of approximately 800 Mbytes. This International Standard specifies extensions and modifications to the recorded format that is described in International Standard ISO/IEC 11559. These extensions and modifications — increase the number of tracks recorded on the tape from 18 to 36. Actual recordings will be made 18 tracks at a time requiring two complete passes of the tape, one from the beginning of tape to the end of tape and the other from the end of tape to the beginning of tape; — specify a different method of defining the ECC characters used to detect and correct errors when the data is read from the tape.