A circular optical disc made up of thin platted glass and plastic polycarbonate material.
Size of DVD's is same as CD's i.e. size of disc is 12 cm, center hole is of 1.5 cm and 1.2 mm in thickness.
Storing of data can be done on both side in a spiral way of valleys (pits) and plains (lands).
DVD uses 650 nm wavelength laser diode light, while CD uses 780 nm. This allows smaller pit to be etched on media surface compare to CD's, granting for DVD's to increase storage capacity.
DVD comes in two format i.e. single layer and dual layer.
Disc with dual layer has capability to access the second layer by shining the laser through first semi-transparent layer.
Storage capacity : One sided single layer - 4.7 GB One sided double layer - 8.5 GB Double sided single layer - 9.4 GB Double sided double layer - 17 GB.
Thus a DVD has 6 times greater capacity than a CD.
Types
DVD-ROM
Contents of DVD cannot be written on or erased by the user.
Used to distribute large amount of databases and applications.
DVD-R / DVD+R
Write once recordable format.
DVD-R (DVD minus R) and DVD+R (DVD plus R) are two different kinds of disc.
Virtually there is no difference between them and both the DVD's are supported by modern devices.
DVD-RW / DVD+RW
Rewritable disc allowing up to 1,000 rewrites before it is used up.
There is no much more difference in -RW and +RW.
DVD-RAM
DVD-RAM (DVD - Random Access Memory) has higher data security and storage capacities.