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112 Everything You Ever Wanted to Know About DVD<br />
What Is BCA?<br />
BCA stands for burst cutting area, a zone near the hub of a DVD reserved<br />
for a barcode that can be etched into the disc by a YAG laser. Because barcode<br />
cutting is independent of the stamping process, each disc can have<br />
unique data recorded in the BCA, such as a serialized ID. DVD readers can<br />
use the laser pickup head to read the BCA. The BCA is used by CPRM<br />
(refer to “What Are the Copy Protection Issues?” in <strong>Chapter</strong> 1) and Divx (see<br />
“What is Divx?” in <strong>Chapter</strong> 2) to uniquely identify each disc.<br />
How Long Do DVDs Last?<br />
Pressed discs (the kind that movies come on) last longer than you will, anywhere<br />
from 50 to 300 years. The expected longevity of dye-based DVD-R<br />
and DVD�R discs is anywhere from 40 to 250 years, about as long as CD-R<br />
discs. The phase-change erasable formats (DVD-RAM, DVD-RW, and<br />
DVD�RW) have an expected lifetime of 25 to 100 years.<br />
A good discussion of CD-R longevity and test info can be found at the<br />
Kodak web site. Also see www.ee.washington.edu/conselec/CE/kuhn/<br />
otherformats/95x9.htm and www.cd-info.com/CDIC/Technology/CD-R/<br />
Media/Kodak.html for more info.<br />
For comparison, magnetic media (tapes and disks) last 10 to 30 years,<br />
high-quality, acid-neutral paper can last 100 years or longer, and archivalquality<br />
microfilm is projected to last 300 years or more. Note that computer<br />
storage media often becomes technically obsolete within 20 to 30 years,<br />
long before it physically deteriorates. In other words, before the media<br />
becomes unviable, it may become difficult or impossible to find equipment<br />
that can read it.<br />
What About the HD-DVD and Blue Laser Formats?<br />
HD-DVD (HD stands for both high-density and high-definition) was under<br />
development before DVDs came out and finally emerged in 2003 (refer to<br />
“Will High-Definition DVDs or 720p DVDs Make Current Players and Discs<br />
Obsolete?” in <strong>Chapter</strong> 2 for general info). Some high-definition versions of<br />
HD-DVD use the original DVD physical format but depend on new videoencoding<br />
technology, such as H.264, to fit high-definition video in the space<br />
that used to hold only standard-definition video. High-density formats use<br />
blue or violet lasers to read smaller pits, increasing the data capacity to<br />
around 15 to 30 GB per layer. High-density formats use high-definition<br />
MPEG-2 video (for compatibility with ATSC and DVB HD broadcasts, refer<br />
to “Do DVDs Support HDTV (DTV)? Will HDTV Make DVDs Obsolete?” in
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