DVD

Digital Versatile Disk/DVD is a popular optical disc storage media format. Its main uses are video and data storage. Most DVDs are of the same dimensions as compact discs but store more than six times as much data.

The basic types of DVD are referred to by a rough approximation of their capacity in gigabytes.

The 12 cm type is a standard DVD, and the 8 cm variety is known as a mini DVD. These are the same sizes as a standard CD and a mini CD, respectively. The capacity by surface (MiB/cm²)differs from 6.92MiB/cm² in the DVD-1 to 18.0 MiB/cm² in the DVD-18

DVD uses 650nm wavelength laser diode light as opposed to 780 nm for CD or 405 nm for HD-DVD or Blu-ray Disc. This permits a smaller pit to be etched on the media surface (1.32 µm for DVD versus 1.6 µm for CD) compared to CDs.

Writing speeds for DVD were 1×, that is 1350 kB/s (1318 KIB/s), in the first drives and media models. More recent models at 18× or 20× have 18 or 20 times that speed. Note that for CD drives, 1× means 150 KIB/s (153.6 kB/s), approximately 9 times slower.

DVD recordable discs supporting this technology are backward compatible with some existing DVD players and DVD-ROM drives^. Many current DVD recorders support dual-layer technology, and the price is now comparable to that of single-layer drives, though the blank media remains more expensive. The recording speeds reached by dual-layer media are still well below those of single-layer media.

There are two modes for dual layer orientation. With parallel track path (PTP), used on DVD-ROM, both layers start at the inside diameter (ID) and end at the outside diameter (OD) with the lead-out. With opposite track path (OTP), used on DVD-Video, the lower layer starts at the ID and the upper layer starts at the OD, where the other layer ends, they share one lead-in and one lead-out