AOR, while still based on the rotation concept, focused on the album as a whole (rather than singles). In the early 1970s, many DJs had the freedom to choose which track(s) to play off a given album—as well as latitude to decide in what order to play the records. Consequently, AOR radio gave mainstream exposure to album tracks that never became hits on the record charts that were limited to singles; "Billboard", for instance, did not establish an airplay chart for album tracks until 1981.