DVD layers. Coloured scanning electron micrograph (SEM) of the pitted layers that encode information on a DVD (digital versatile disc). The pits are read by a focused laser as the disc rotates. This is a double-layer DVD, which can hold up to 8.5 gigabytes (GB) of information. One layer (gold) is semi-transparent. A second layer (silver) is bonded to the gold layer by a clear adhesive layer (grey). After the laser has read the information on the gold layer (from the centre of the disc outwards), the laser refocuses itself on the silver layer and reads from that, from the outer edge inwards. Magnification: x700 at 6x7cm size.