DVD recordable is commonly known as DVD-R format, which generally has a storage capacity of 4.71 GB, as compared to the original pioneer DVD’s capacity of 3.95 GB.
These values are of huge importance, and as a matter of fact the 700 MB CD-R is very low on storage capacity as compared to a DVD-R, which has 6.4 times the total capacity of a regular CD-R.
The DVD-R format first came into existence with the help of professionals working for Pioneer. It was the year 1997, when these high quality DVDs were launched which is supported by most DVD players, and also has got approval by the DVD Forum.
There is no mystery in the achievement of this large storage capacity DVD-R. It is done by reducing the pit sizes and also making smaller track pitch of the groove spiral that in turn gives orders to the laser beam. Now, this may be noticeable that you can write more and more pits on the same physical sized disc.
A comparatively low wavelength of 650 nm is used in conjunction alongside a higher numerical aperture lens therefore writing smaller pits onto the recording dye layer, a red laser beam is used here. Due to this shorter wavelength, DVD-R use different dyes as compared to CD-R. This way the wavelength is properly absorbed. Two 0.6 mm polycarbonate discs are bonded with an adhesive to each other to compose a DVD-R disc. The recording dye and a silver alloy or gold reflector is coated on one disc which also contains the laser guiding groove.
The data is protected against scratches by the sandwich structure-containing layer by a thick “dummy” disk. Nowadays these kind of DVDs are widely used, both for legal and illegal purposes. These DVDs are also available in the market storing huge amount of 80s classical porn movies. Commonly known as 80s porn DVDs (for the adults), these are best sellers.
LINK - interesting read
http://en.wikipedia.org/