aNAREXIA...reading a DVD on a standard CD-ROM is impossible. Its physics mate!
As was pointed out by VIPER_1069, DVD's have a far greater density of digital information. Standard CD's are 650megabytes and at most 700mb for standard pressed CD's.
DVD's on the other hand have 4.7 Gigabytes per side of digital information.
The reason a DVD can put that much more information (ie, density) is that it uses a UNIQUE red laser that uses a thinner beam with a shorter wavelength that can accurately read the
more densely packed information. So you know, this "unique" red laser is very near the blue light spectrum.
Regular CD's on the other hand, use a standard red laser. Now any first year Physics student knows that the light ray measurement (its measured in nanometers, BTW
) of a blue light ray is much smaller than a red one.
Thus it is impossible for a CD-ROMs red laser to read the much higher density info of a DVD. It would be analogous of trying to listen to a vinyl record with a ballpoint pen instead of a stylis needle. The ballpoint pen is just to big.
Plus, since the 3rd generation DVD players, the lasers are unique because of a new DVD technology... doubled-layered disc.
These disks use a two-layer process. This entails an efficient method of constructing a double-layered disc where the laser would read the first layer, then pass through a semi-transparent gold layer to read the second...which is positioned less than 1/2 the width of a human hair below it. This also upps the storage capacity to 8.5 gigabytes on a single side.
With me so far, right?!...good
Now, you may ask how is a DVD-ROM backward compatable with a CD. It does it with a dual-focus hologram lens that splits the beam of the laser so that it can read two different levels at the same time...a depth of 0.6mm for DVD discs and 1.2mm for CDs. This eliminates the need for 2 separate laser systems and ensures full compatibility with your existing CD and CD-ROMs.
CD-ROMs do not use these kind of lasers because or the costs involved. And if they did...why wouldn't you advertise it as such?!
Hope this answers some questions.