February 25th, 2006
|
 | Valued Member contributor | | Join Date: February 20th, 2005 Location: Depends on the Day
Posts: 3,012
| |
Yes, The quote below is from Wikipedia Quote: |
DVDs are made from a 0.6 mm thick disc of polycarbonate plastic coated with a much thinner reflective layer of aluminium or gold. Two such discs are glued together to form a 1.2 mm disc that can be designed to be read from one side (single sided) or both sides (double sided). The substrates are half as thick as a CD to make it possible to use a lens with a higher numerical aperture and therefore use smaller pits and narrower tracks. Discs commonly come in 8cm or 12cm diameters.
| Quote: |
A single-layer DVD can store 4.7 GB (4.38 GiB), which is around seven times as much as a standard CD-ROM. By employing a red laser at 650 nm wavelength (compared to 780 nm for CD) and a numerical aperture of 0.6 (compared to 0.45 for CD), the read-out resolution is increased by a factor 1.65. This holds for two dimensions, so that the actual physical data density increases by a factor of 3.5. DVD uses a more efficient coding method in the physical layer. CD's error correction, CIRC, is replaced by a powerful Reed-Solomon product code, RS-PC; Eight-to-Fourteen Modulation (EFM) is replaced by a more efficient version, EFMPlus, which uses eight-to-sixteen modulation. There is no subcode as in CD. As a result, the DVD format is 47 percent more efficient with respect to CD-ROM, which uses a "third" error correction layer.
|
__________________
 
A little common sense goes a long way
Later Grandpa |