Hardware Reference
In-Depth Information
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
pickupcanaccuratelyreadbits(pit/landtransitions)spacedaslittleasonly0.4micronsor
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, res-
ulting in slightly less information being stored in each layer.
Table 11.8 DVD Technical Parameters
