Perhaps one great irony of popular music is that in terms of its cultural circulation and economic model, it has returned in part to its early 20th century roots. At the beginning of the 20th century, popular music circulated via live performance. The technologies of recording enabled it to develop radio and television as both distribution and royalty channels. Recording technology also led to record, then CD, sales being a major economic force with live concerts used mainly to promote those sales. With the advent of internet distribution, the major revenue stream for popular music has returned to live performance.