High Quality Content by WIKIPEDIA articles! The Holographic Versatile Disc (HVD) is an optical disc technology. It can hold many times the amount of information as a Blu-ray disc. It employs a technique known as collinear holography, whereby two green laser beams are collimated in a single beam. The green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc. A Blue laser is used as the reference beam to read servoinformation from a regular CD-style aluminum layer near the bottom. Servoinformation is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servoinformation is interspersed amongst the data.