This part of IEC 1120 applies to stereophonic digital audio recording on 6,3 mm wide tape with stationary heads for professional use. It defines the mechanical and electrical characteristics necessary to ensure the interchangeability of programme recorded digital audio signal on magnetic tape amongst professional industries. This standard is presented in three parts. Parts 2 and 3 describe two formats usable within part 1. It is practical to have switchable operation between these two formats. Consequently it is logical to include both in one standard.