Tomorrow marks half of century since the largest one day concert was held at the Ontario Motor Speedway in California, on April 6th 1974. In front of a huge crowd (over 300 thousand), eight rock bands performed throughout the day. Three headliners were British bands: Black Sabbath, Emerson Lake & Palmer and Deep Purple. Purple's performance became an iconic due to Ritchie Blackmore's spectacular finale, with exploding amplifies and smashed TV cameras. You can hear the interviews with Bill Ward, Keith Emerson and all Deep Purple Mk3 members, sharing their memories regarding the whole festival.