DVD Demystified

Disc and Data Details
Figure 5.12
Disc organization
surface. Accordingly, there are more data sectors per revolution further
from the center of the disc. Some units spin the disc at a CAV, keeping the
revolutions per minute the same regardless of the position of the pickup
head. They use more advanced circuitry to deal with the difference in data
readout rates. These units only achieve their maximum rated speed when
reading the outermost section of the disc.
DVD-ROM, DVD-R, and DVD-RW media are formatted for CLV reading.
DVD+RW media can be formatted in either CLV or CAV mode. In CAV
mode, there are always the same number of sectors per revolution. Since
data toward the outer edge of the disc is spread across more surface area in
CAV mode, the capacity of the disc is reduced. The advantage of CAV is that
seeking to a specific sector is faster because the motor does not have to
speed up or slow down as the head travels in or out.
DVD-RAM uses a combination of CLV and CAV formatting, called zoned
CLV (ZCLV). Details are in the previous DVD-RAM section.
File Format
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Data sectors on a DVD-ROM can contain essentially any type of data in any
format. Officially, the OSTA UDF file format standard is mandatory. UDF
defines specific ways in which the ISO 13346 volume and file structure
standard is applied for specific operating systems.