Though classical music is very much a living tradition today, it also has a thousand-year history of having been preserved for posterity by musical notation. Popular music, sometimes notated but often including spontaneous elements, has a deep history of its own, of course. Yet our knowledge of music that was never written down is limited to a period beginning just over a century ago, when the first recordings were made. Notation allows, if not greater complexity, at least a greater degree of control over musical events on the part of a composer external to a given performance of a piece. Whereas a pop recording, very broadly speaking, depends on an interaction between performer and song, classical music rests on a triad: composer, work, and performer.