Bill Monroe's version is a mountain waltz refined on his first Columbia session with Lester Flatt and Earl Scruggs. Under a blue Kentucky moon it sings longing for home — while mandolin chops and three-finger banjo rolls codify bluegrass's acoustic ensemble language.
Elvis's version recuts the same song in a driving 4/4. A slapped upright bass and a leaping voice capture the moment a country song is sung as rock and roll — and it became one side of the first single pressed at Sun Records.