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DVD Demystified

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182<br />

Figure 4.4<br />

<strong>DVD</strong> layers<br />

Chapter 4<br />

drives intended to read recordable CDs must include a second 780nanometer<br />

laser.<br />

The remaining task to ensure CD compatibility merely requires an<br />

extra bit of circuitry and firmware for reading CD-format data. However,<br />

the CD family is quite large and includes some odd characters, not all of<br />

which fit well with <strong>DVD</strong>. The prominent members of the CD family are<br />

audio CD, Enhanced CD (or CD Plus), CD-ROM, CD-R, CD-RW, CD-i,<br />

Photo CD, CDV, and Video CD. It would be technically possible to support<br />

all these, but most of them require specialized hardware. Therefore, most<br />

manufacturers choose to support only the most common or easy-to-support<br />

versions. Some, such as Enhanced CD and Video CD, are easy to support<br />

with existing hardware. Others, such as CD-i and Photo CD, require<br />

additional hardware and interfaces, so they are not commonly supported.<br />

However, since the data on a CD can be read by any <strong>DVD</strong> system, conceivably<br />

any CD format could be supported. <strong>DVD</strong>-ROM computers support<br />

more CD formats than <strong>DVD</strong> players partly because some are<br />

designed for computer applications and partly because specialized CD<br />

systems can be simulated with computer software. See Chapter 8 for<br />

details of the different CD formats and the compatibility of <strong>DVD</strong>-Video<br />

and <strong>DVD</strong>-ROM with each.

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