Piano four hands is the common name for a piano duet in which both players play on the same instrument (this differentiates it from a standard piano duo, with separate instruments for each performer). Although original music has been written for this type of duet, by far most of the repertoire for piano four hands consists of arrangements and versions of other ensembles. These were particularly popular before the coming of recording technology, as they provided a way to hear popular works of music outside the concert hall, and when playing an orchestral work, two players could achieve some effects that a single player could not.