Hardware Reference
In-Depth Information
lead-in zone starts at a radius of 22mm from the center of the disc. The data zone starts at a radius of
24mm from the center and is followed by the lead-out (or middle) zone at 58mm. The disc track
11.10
shows these zones in actual relative scale as they appear on a DVD.
Figure 11.10. Areas on a DVD (side view).
Officially, the spiral track of a standard DVD starts with the lead-in zone and ends at the finish of the
lead-out zone. This single spiral track is about 11.84 kilometers or 7.35 miles long. An interesting
fact is that in a 20x CAV drive, when the outer part of the track is being read, the data moves at an
actual speed of 156 miles per hour (251km/h) past the laser. What is more amazing is that even when
the data is traveling at that speed, the laser pickup can accurately read bits (pit/land transitions)
spaced as little as only 0.4 microns or 15.75 millionths of an inch apart!
DVDs come in both single- and dual-layer as well as single- and double-sided versions. The double-
sided discs are essentially the same as two single-sided discs glued together back to back, but subtle
differences do exist between the single- and dual-layer discs.
Table 11.8
shows some of the basic
information about DVD technology, including single- and dual-layer DVDs. The dual-layer versions
are recorded with slightly longer pits, resulting in slightly less information being stored in each layer.
Table 11.8. DVD Technical Parameters
