What are DVD-R discs?
DVD-R discs are recordable DVD media that can be written to only once. The discs can be writen in standard DVD writer drives. The DVD-R format was developed by Pioneer in 1997 and is the most commonly used type of writable DVD (other types include DVD+R and the re-writable DVD-RW/DVD+RW).
DVD-R discs have much higher storage capacities than CD-R discs by using smaller pit sizes and narrower track pitches in the spiral groove that runs around the discs. These smaller pits and grooves require a different wavelength of laser light (650nm) to that used in CD drives (780nm) and therefore DVD discs cannot be read in standard CD drives.
The DVD-R discs are available in two main sizes of circular diameter 12cm and 8cm. The 12cm discs are the typical size for CDs and DVDs and have a capacity of 4.7GB and the 8cm discs have a capacity of 1.4GB.
DVD-R discs are made from two 0.6mm polycarbonate layers that are bonded to each other. One of the layers contains a grooved reflective surface and a recording dye (hence the slightly green/blue colouring of DVD-R discs when compared to replicated discs). The other layer is just clear and is used to create the required disc thickness of 1.2mm.
Below is a diagram illustrating the difference in track pitch between CDs and DVDs: