the folk harp is the older kind of harp, the oldest dating back to 3000 bc in ancient egypt. in these harps, each string can only make one note at a time. they are usually tuned so that playing each string in order sounds like playing all the white notes on a piano in order. this is called a diatonic scale. in some places, they are tuned so that playing each string in order sounds like playing all the black notes on a piano in order. this is called a pentatonic scale.