DVD Media and DVD R-Media Specs
DVD is an optical disc storage media format that can be used for storing data,
including video games and 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 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
thinner (reflective) aluminum layer. Two 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 Gigabytes, 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. DVDs use a more efficient coding method in
the physical layer. CDs 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, EFM Plus, which has the same characteristics as
classic EFM. The CD sub-code is removed. As a result, the DVD format is 47%
percent more efficient with respect to CDROMs, 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 = Re-Writable)
DVD-RAM (random access rewritable; after-write checking of data integrity is
always active.)
DVD+R/RW (R=Recordable once, RW = Re-Writable)
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 (Gigabytes)
DVD-9: single sided, double layer, 8.5 GB (7.92 Gigabytes)
DVD-10: double sided, single layer on both sides, 9.4 GB (8.75 Gigabytes)
DVD-14: double sided, double layer on one side, single layer on other, 13.3 GB
(12.3 Gigabytes)
DVD-18: double sided, double layer on both sides, 17.1 GB (15.9 Gigabytes)
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. |
