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 freedom to play long sets of music, often covering a variety of genres. Songs were not limited to hits or singles; indeed the DJs often played obscure or longer tracks by newer or more adventurous artists than 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.