In the USA basically AM radio played the top 40 hits on their stations .
In the 1970's FM radio started playing songs off albums that weren't necessarily the hits.
Blue Oyster Cult-Career of Evil
David Bowie-Aladdin Sane
Eric Clapton-Just One Night
Harvey Danger-Where Have All the Merrymakers Gone ?
Kiss-Sonic Boom
Ted Poley-Collateral Damage
Radio Active Cats-S/T
Weashuman-S/T