Whats a dual-layer disc?
A dual-layer disc has two layers of data, one of them semi-transparent so that the laser can focus through it and read the second layer. Since both layers are read from the same side, a dual-layer disc can hold almost twice as much as a single-layer disc, typically 4 hours of video. Many discs use dual layers. The advantage of two layers is that long movies can use higher data rates for better quality than with a single layer.
