Sony Handycam DCR-DVD100 Technology Handbook page 9

DVD Capacity
DVD-ROM, DVD-R and DVD-RW discs 12cm (4-3/4") in
size, which all share the same "one layer, one side"
structure, have a storage capacity of 4.7 GB --
approximately 7 times larger than the capacity of a CD
disc the same size. DVD Handycam camcorders use
smaller DVD-R or DVD-RW discs 8mm (3-1/8") in size.
12cm (4-3/4")-diameter disc
About Lasers and Lenses
DVD recording uses a short-wavelength red semiconductor laser. The wavelength of this laser is 650nm (nanometers). The
NA (numerical aperture) of the object lens used for optical pickup is 0.6. This combination yields a small-diameter "spotlight"
and high-density recording capacity. By comparison, CD recording uses a semiconductor laser with a wavelength of 780nm
and a NA of 0.45.
Comparison of CD-ROM and DVD-ROM
CD-ROM
Track pitch
1.6µm
4.7
GB
the minimum
pitch size
0.83µm
diameter of spot
1.4µm
These smaller discs, single-sided with one recordable
layer per side, have storage capacity of 1.4 GB. Small
double-sided discs with one recordable layer per side are
also available for DVD Handycam camcorder recording;
these discs have a storage capacity of 2.8 GB -- enough
to hold approximately two hours of video recording.
8cm (3-1/8")-diameter disc
1.4
GB
DVD-ROM
Track pitch
0.74µm
D V D H a n d y c a m T E C H N O L O G Y H A N D B O O K
the minimum
pitch size
0.4µm
diameter of spot
0.9µm
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