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64 Everything You Ever Wanted to Know About DVD<br />
Is CD Compatible with DVD?<br />
This actually has many answers, covered in the following sections. Note the<br />
differentiation between DVDs (general media) and DVD-ROMs (computer<br />
data).<br />
Is CD Audio (CD-DA) Compatible with DVDs?<br />
All DVD players and drives will read audio CDs (Red Book). This is not actually<br />
required by the DVD spec, but so far all manufacturers have made their<br />
DVD hardware able to read CDs.<br />
On the other hand, you can’t play a DVD in a CD player. The pits are<br />
smaller, the tracks are closer together, the data layer is a different distance<br />
from the surface, the modulation is different, and the error correction<br />
coding is new. Also, you can’t put CD audio data onto a DVD and<br />
have it play in DVD players (Red Book audio frames are different from<br />
DVD data sectors.)<br />
Is CD-ROM Compatible with DVD-ROM?<br />
All DVD-ROM drives will read CD-ROMs (Yellow Book), and software on a<br />
CD-ROM will run fine in a DVD-ROM system. However, DVD-ROMs are not<br />
readable by CD-ROM drives.<br />
Is CD-R Compatible with DVD?<br />
Sometimes. The problem is that most CD-R discs (Orange Book Part II) are<br />
“invisible” to the DVD laser wavelength because the dye used to make the<br />
blank CD-R doesn’t reflect the beam. Some first-generation DVD-ROM drives<br />
and many DVD players can’t read CD-R discs. The formulation of dye<br />
used by different CD-R manufacturers also affects readability. That is, some<br />
brands of CD-R discs have better reflectivity at the DVD laser wavelength,<br />
but even these don’t reliably work in all players. An effort to develop CD-R<br />
Type II media compatible with both CD and DVD wavelengths has been<br />
abandoned.<br />
The common solution is for the DVD player or drive to use two lasers at<br />
different wavelengths: one for reading DVDs and the other for reading CDs<br />
and CD-Rs. Variations on the theme include Sony’s dual discrete optical<br />
pickup with switchable pickup assemblies that have separate optics, dualwavelength<br />
lasers (initially deployed on Sony’s PlayStation 2), and Samsung’s<br />
annular masked objective lens with a shared optical path. Other<br />
approaches include Toshiba’s shared optical path using an objective lens<br />
masked with a coating that’s transparent only to 650-nanometer light,
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