Album Oriented Rock was a popular format from the mid 1970s through the early 1980s in the USA that was popularized by the then booming media called FM radio. AOR was popularized by the fact that most pop rock stations tended only to play the hit singles of many artists, while ignoring many deserving songs that were either too long, or were simply not designated singles. It was a fairly cool format for its time, since albums by bands such as Led Zeppelin, Bruce Springsteen, Rush, Pink Floyd, and Yes to name a few often were best listened to as a complete album, or at least they often had several very good songs on them. You rarely heard such masterpieces such as Echoes or Kashmir, except at 4AM, but you heard a lot more than on the pop stations of the time.
On the east coast, a couple of good examples of these AOR stations were WIYY in Baltimore, WMMR and WYSP in Philadelphia, and WNEW in New York. As a rule, these stations limited themselves to proven artists who had several successful albums, and who had that certain "sound". One cool thing they did for a while was to play entire record albums on Sunday Night, until pressure from the RIAA forced them to stop due to concerns that home taping was cutting into record sales. I still have a few of those old tapes, but many have been lost due to the ravages of time, malfunctioning cassette decks, and car breakins.
As musical tastes changed in the 1980s, AOR had a hard time keeping up. Rock and roll diversified into several different genres such as punk, alternative rock, hair bands, and heavy metal. A few bands fit in, such as Van Halen, U2, Metallica and Dire Straits but many of the best bands of the 1980s found a new voice under the banner of alternative rock. The artists who provided the mainstay for AOR also started to die off. 1977 saw the death of Lynyrd Skynyrd as a creative force in a plane crash. In the next few years Keith Moon of The Who and John Bonham of Led Zeppelin fell victims of substance abuse. The deaths of Moon and Bonham caused the breakup of The Who and Led Zeppelin, while personality conflicts caused other bands to lose key members, such as what happened when Roger Waters left Pink Floyd after the album The Final Cut.
As a result of this attrition, and the rise of alternative rock stations such as WHFS (before they sold out), WPRB out of Princeton, New Jersey and many college radio stations, AOR suffered an identity crisis. Often they recoined themselves as Classic Rock stations, forever enshrining such tunes as Stairway to Heaven, or they vascillated between formats, playing hair bands for a while, then going back to classic rock, then trying heavy metal or a mix format. Classic rock formats probably capture the AOR experience about as well as anything, but their listeners have aged past the point of being a desirable demographic for advertisers. The remaining stations that have classic rock formats increasingly have that annoyingly low-budget sound of compressed audio, canned deejays, and a playlist consisting mostly of overplayed greatest hits by bands who sold out to corporate rock. Although I grew up loving most of the music played by the AOR stations of old, I hold the current crop of classic rock stations in nearly the same disdain I held for easy listening stations when I was growing up.