DVD disc facts
A DVD-Recordable or DVD-R is an optical disc with a larger storage capacity than a CD-R, typically 4.7 GB (4.38 GB) instead of 700 MB, although the capacity of the original standard was 3.95 GB. Pioneer developed the 8.54 GB dual layer version, launched in 2005. A DVD-R can be written to only once, whereas a DVD-RW (DVD-rewritable) can be rewritten multiple times. The DVD-R format was developed by Pioneer in autumn of 1997. It is supported by most DVD players, and is approved by the DVD Forum.
DVD discs are the same diameter (120mm) and thickness (1.2mm) as a Compact Disc but a DVD can store 13 times or more data contained on a CD. Factoring in DVD’s capability to record on both sides of the disc offers 26 times the storage capability a CD. Unlike a CD, a DVD is a bonded disc, made of two 0.6 mm substrates joined together.
At an average bit rate of 4.5Mbs, a single sided DVD disc has the playback capability of 133 minutes of the highest quality audio and video images. That’s nearly 92% of all Hollywood titles ever made! Dual layer DVD disc can provide up to 4 hours of playback.
Optical disc authoring, including CD authoring and DVD authoring, is known as cloning, burning or ripping, the process of recording source material onto an optical disc (CD or DVD). Cloning software is required.
A DVD has a recording layer coated in an organic dye. A DVD burning laser, of higher intensity than a typical DVD reading laser, etches patterns into the dye, allowing the data to be read at a later date. A rewritable DVD uses a special metal alloy instead of a dye. The alloy can be switched back and forth between an amorphous and crystalline phase through the application of a laser, allowing the DVD to be rewritten a substantial number of times. Data quality degrades if the DVD is rewritten excessively, however.
Creating an optical disc usually involves first creating a disk image with a full file system designed for the optical disc, and then actually burning the image to the disc. Many programs create the disk image and burn in one bundled application, such that end-users do not even know the distinction.
The speed at which a DVD can be ripped is expressed as a multiplier: 16X means 16 times faster than just playing it.
DVD discs will not deteriorate over time and are unaffected by magnetic fields (which can literally erase a VHS cassette).
Video : CD/DVD media types explained