Instead, the IMAX system specifies a separate six-channel 35 mm magnetic film, recorded and played back on a film follower locked to picture, just as Vitaphone had been (utilizing 16-inch 33 1/3 RPM electrical transcription discs) in the early 20th century, and was the same technology used to provide the 7-channel soundtrack accompanying films photographed and exhibited in the Cinerama process in the mid-1950s.