“The DIN connector is an electrical signal connector that was standardized by the Deutsches Institut für Normung (DIN), the German Institute for Standards, in the mid 1950s, initially with three pins for mono, but when stereo connections and gear appeared in the late 1950s, versions with five pins or more were made.”… …“In consumer electronics, the cylindrical connectors were adopted for analog audio signals.[3] Some DIN connectors have been used in analog video applications, for power connections, and for digital interfaces, such as the MIDI (DIN 41524), the IBM PC keyboard and the IBM AT keyboard connectors (DIN 41524).”