What is a dual-layer disc?
It is a type of DVD with double the storage capacity of standard discs. It contains two recording/ data layers. A transparent spacer is exist between the two recording layers. Semitransparent reflector layer of first recording layer accepts the laser to access data which is then passes to the second layer. Recording of first layer starts from inner edge to outer edge, where as in the second layer it is from outer to inner.
