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.