In computing, soun reproduction, and video, an optical disc is a flat, circular disc (usually polycarbonate) wherein data are stored in the pits (or bumps) in its flat surface — sequentially on the continuous, spiral track extending from the innermost track to the outermost track, covering the entire disc surface. The data are accessed in the disc when a special material (often aluminium) is illuminated with a laser diode. The pits distort the reflected laser light, hence, most optical discs (except the black discs of the original PlayStation toy), characteristically have an iridescent appearance created by the grooves of the reflective layer.