Album-oriented rock (AOR, originally called album-oriented radio) is an FM radio format created in the United States in the 1970s that focuses on the full repertoire of rock albums and is currently associated with classic rock. Album-oriented radio was originally established by U.S. radio stations dedicated to playing album tracks by rock artists from the hard rock and progressive rock genres. In the mid-1970s, AOR was characterized by a layered, mellifluous sound and sophisticated production with considerable dependence on melodic hooks. Using research and formal programming to create an album rock format with greater commercial appeal, the AOR format achieved tremendous popularity in the late 1970s and early 1980s. From the early 1980s onward, the "album-oriented radio" term became normally used as the abbreviation of "album-oriented rock," meaning radio stations specialized in classic rock recorded during the late 1960s and 1970s. The term is also commonly conflated with "adult-oriented rock", a radio format that also uses the initialism "AOR" and covers not only album-oriented rock but also album tracks and "deep cuts" from a range of other rock genres, such as soft rock and pop rock. History Freeform and progressive The album-oriented rock radio format started with programming concepts rooted in 1960s idealism. The freeform and progressive formats developed the repertoire and set the tone that would dominate AOR playlists for much of its heyday. In July 1964, the U.S. Federal Communications Commission (FCC) adopted a non-duplication rule prohibiting FM radio stations from merely running a simulcast of the programming from their AM counterparts. Owners of AM/FM affiliate stations fought these new regulations vigorously, delaying the enactment of the new rules until January 1, 1967. When finally enacted, station owners were pressed to come up with alternative programming options. The freeform format in commercial radio was born out of the desire to program the FM airwaves inexpensively. Programmers like Tom Donahue at KMPX in San Francisco developed stations where DJs had the freedom to play long sets of music, often covering a variety of genres. Songs were not limited to hits or singles; DJs often played obscure or longer tracks by newer or more adventurous artists rather than those heard on Top 40 stations of the day. This reflected the growth of albums as opposed to singles as rock's main artistic vehicle for expression in the 1960s and 1970s. With a few exceptions, commercial freeform had a relatively brief life.