Sony DCR-DVD200 DVD Handycam Technology Handbook - Page 9

DVD MEDIA TECHNOLOGY 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. 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. 12cm (4-3/4")-diameter disc 8cm (3-1/8")-diameter disc 4.7GB 1.4GB 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 DVD-ROM Track pitch 1.6µm the minimum pitch size 0.83µm diameter of spot 1.4µm the minimum pitch size 0.4µm diameter of spot 0.9µm Track pitch 0.74µm 9 DVD Handycam TECHNOLOGY HANDBOOK