Helical scan

 A type of videotape, data, or audio recorder in which the tape is wrapped around a large rotating drum, on which the actual record and playback heads are mounted. Since the heads rotate quickly and write parallel tracks at a very small angle with respect to the tape path, the signal written on the tape is may times the actual length of the tape itself. Thus, helical scan recording offers very high resolution at low tape speeds. Almost all consumer and professional videotape formats employ the helical scan principle, largely replacing the quadruplex recorder.