Profile about DVD Media(http://www.cdrdvdrmedia.com)
DVD is an optical disc storage media format that can be used for
storing data, including movies with high video and sound
quality. DVDs resemble compact discs: their physical dimensions
are the same?12cm or the mini 8cm?but they are encoded in a
different format and at a much higher density. Unlike CDs, all
DVDs must contain a file system. This file system is called UDF,
and is an extension of the ISO 9660 Standard used for Data-CDs.
DVDs are made from a 0.6 mm thick disc of polycarbonate plastic
coated with a much thinner (reflective) aluminium layer. Two
such discs are glued together to form a 1.2 mm double-sided
disc. The basic DVD disc is thinner than a CD to make it
possible to use a lens with a higher numerical aperture.
A single-layer DVD can store 4.7 Gbyte, which is around seven
times more than a standard CD-ROM. By employing a read laser at
650 nm (was 780 nm) wavelength and a numerical aperture of 0.6
(was 0.45), 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 has the same
characteristics as classic EFM. The CD subcode is removed. As a
result, the DVD format is 47% percent more efficient with
respect to CD-ROM, which uses a 'third' error correction layer.
DVD Media can contain: DVD-ROM (read only, manufactured by a
press) DVD-R/RW (R=Recordable once, RW = ReWritable) DVD-RAM
(random access rewritable; after-write checking of data
integrity is always active.) DVD+R/RW (R=Recordable once, RW =
ReWritable)
Two DVDs with different bottom sides.The disc may have one or
two sides, and one or two layers of data per side; the number of
sides and layers determines the disc capacity.
DVD-5: single sided, single layer, 4,704,317,440 bytes, 4.7
gigabytes (GB), or 4.38 gibibytes (GiB) DVD-9: single sided,
double layer, 8.5 GB (7.92 GiB) DVD-10: double sided, single
layer on both sides, 9.4 GB (8.75 GiB) DVD-14: double sided,
double layer on one side, single layer on other, 13.3 GB (12.3
GiB) DVD-18: double sided, double layer on both sides, 17.1 GB
(15.9 GiB) The capacity of a DVD-ROM can be visually determined
by noting the number of data sides, and looking at the data
side(s) of the disc. Double-layered sides are usually
gold-colored, while single-layered sides are silver-colored,
like a CD. One additional way to tell if a DVD contains one or
two layers is to look at the center ring on the underside of the
disc. If there are two barcodes, it is a dual layer disc. If
there is one barcode, there is only one layer.
Each medium can contain any of the above content and can be any
layer type. Double layer DVD+R discs are already on the market.
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