This International Standard specifies the physical and magnetic characteristics of magnetic tape cassettes@ using magnetic tape 12@65 mm wide so as to provide physical interchange of such cassettes between drives. It also specifies the quality of the recorded signals@ the recording method and the recorded format@ called Digital Tape Format-l (DTF-I)@ thereby allowing data interchange between drives by means of such cassettes. The format supports variable length Logical Records@ high speed search@ and the use of a registered algorithm for data compression. This International Standard specifies two sizes of cassette. For the purposes of this International Standard the larger cassette is referred to as Type L@ and the smaller as Type S. Together with a standard for volume and file structure@ e.g. IS0 1001@ this International Standard provides for full data interchange between data processing systems.