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114 Everything You Ever Wanted to Know About DVD<br />
Advanced Optical Disc (AOD), aka DVD2<br />
The DVD Forum’s next-generation DVD is Advanced Optical Disc (AOD), or<br />
DVD2. AOD is a modification of the existing DVD physical format to enable<br />
about 15 GB per layer using a blue-ultraviolet readout laser. The same 0.6millimeter<br />
data depth is used. AOD is designed to improve data capacity<br />
while theoretically being able to use existing replication equipment. It is primarily<br />
supported by Toshiba and NEC.<br />
Blu-ray Disc (BD)<br />
The Blu-ray Disc (BD) is a new high-density physical format that will hold 23<br />
to 27 GB per layer using a blue-ultraviolet laser and a 0.1-millimeter data<br />
depth. Because of the 0.1-millimeter cover layer, it requires significant<br />
changes to production equipment. Blu-ray is initially intended for home<br />
recording, professional recording, and data recording. Mass-market distribution<br />
of prerecorded movies will come later, after a read-only format is<br />
developed and the details of video, audio, interactivity, and copy protection<br />
are hammered out. The Blu-ray backers include LG, Panasonic, Philips,<br />
Pioneer, Hitachi, Mitsubishi, Samsung, Sharp, Sony, and Thomson. Sony<br />
released the first BD recorder in Japan in April of 2003.<br />
As far as technical details, a BD holds up to 27 GB per layer using a<br />
0.1-millimeter recording depth (to reduce aberration from disc tilt). It uses a<br />
405-nanometer blue-violet semiconductor with 0.85 numerical aperture<br />
(NA) lens design to provide a 0.32 �m track pitch (half that of DVDs) and as<br />
small as a 0.138 �m pit length. Variations include 23.3 GB of capacity with<br />
a 0.160 �m minimum pit length or 25 GB of capacity with a 0.149 �m minimum<br />
pit length. The physical discs will use phase-change groove recording<br />
on a 12-centimeter diameter, 1.2-millimeter-thick disc, similar to<br />
DVD-RW and DVD�RW. It has a 36 Mbps data transfer rate. The recording<br />
capacity on a single layer is about 2 hours of HD video (at 28 Mbps) or<br />
about 10 hours of standard-definition video (at 4.5 Mbps). The cartridge<br />
size is 129 � 131 � 7 millimeters. Plans are to produce dual-layer recordable<br />
discs, holding about 50 GB per side, but such discs will take a few<br />
additional years to appear.<br />
Blue-HD-DVD-1 and Blue-HD-DVD-2<br />
The Advanced Optical Storage Research Alliance (AOSRA), formed by Taiwan’s<br />
Industrial Technology Research Institute (ITRI) has its own variations<br />
of blue-laser formats. Blue-HD-DVD-1 uses a 0.6-millimeter data depth<br />
similar to AOD, and Blue-HD-DVD-2 uses a 0.1-millimeter data depth<br />
similar to Blu-ray.
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