An interesting feature of DVD is that the disk’s second data layer can be read from the inside of the disk out,
as well as from the outside in. I
n standard density CDs, the information is always stored first near the hub of
the disk. The same is true for single-layer and dual-layer DVD, but the second layer of each disk can contain
data recorded ‘backwards’, or in a reverse spiral track. With this feature, it takes only an instant to refocus a lens
from one reflective layer to another. On the other hand, a single-layer CD that stores all data in a single spiral
track takes longer to relocate the optical pickup ...
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