Sony RDR-GX7 - Manual (Page 5)

DVD specifications are configured with three format layers;
the physical format, the logical (sometimes called theoretical)
format and the application format.
The physical format can be likened to the sheet of paper on
which an essay is written. In this case, the paper is the DVD disc
and there are several types, DVD-R DVD+R, DVD-RW,
DVD+RW and DVD-RAM. Each is made with different
materials, and has different specifications and its own distinct
characteristics. For example, an ‘essay’ written on DVD-RW can
be erased and re-written many different times, while an ‘essay’
on DVD-R, due to the nature of the materials it is made of, can
only be written once and cannot be erased.
The logical format can be likened to the way in which letters
are written on the essay paper, plus the lines on the paper which
are necessary for accurate reading. Moreover, if there are no
lines on the paper, then the letters cannot be accurately written
down. These lines determine how the letters and words are to be
written onto the paper and are used to correctly manage the
words themselves. In specific terms, technologies such as UDF
and ISO-9660 represent these ‘lines’ on the paper.
Finally, the application format can be considered the
language of the essay. These ‘languages’ include DVD-Video,
DVD Video Recording, DVD-Audio, and DVD+RW Video. For
example, if an ‘essay’ is written in DVD-Video ‘language,’ it will
have different characteristics than exactly the same ‘essay’
written in DVD-VR ‘language.’ The DVD-Video ‘language’ is
considered the native ‘language’ in the world of DVD players.
Theoretically, this type of DVD recording should be capable of
being be read by any DVD player. Alternatively, if the ‘essay’ is
in the ‘language’ of DVD-VR, it can be freely edited using a
variety of inherent editing functions.
In this chapter we will explain in detail about these three
different format layers.
The Physical Format
The physical format is the specifications of the actual physical
dimensions and characteristics of the disc itself. The external
dimensions of 4.7 Gbytes DVD disc media are exactly the same
as those of a CD, 120 mm in diameter (or 80 mm) and two disc
sides of 0.6 mm each, for a total thickness of 1.2 mm. However,
the materials in the recordable layer and the configuration of disc
sides will vary.
Playback and recording configuration
Reading the signal from the disc is done in the same way as with
other optical disc playback media such as CD and DVD-Video
software, with a laser beam reflecting off the surface of the disc.
The modulations of these reflections are read as ‘0’ or ‘1,’
representing the original digital data. Recording onto the disc
requires a stronger laser beam than that used for playback, since
the laser must heat up the recording material. Write-once discs
such as DVD-R and DVD+R use organic dye in the recording
layer, which chemically changes when exposed to heat. If a
strong laser beam is reflected onto organic dye, it causes a
chemical change that changes the light reflection ratio of that
spot. During playback, the laser reads these spots to extract the
signal from the disc. However, once the chemical change in the
organic dye has occurred, it cannot be changed back to its
original state.
Re-writable discs such as DVD-RW, DVD+RW and DVD-
RAM use a compound which can be phase modulated. In the
recording layer, this phase modulation takes the form of either a
crystalline structure, or an amorphous non-crystalline structure.
If strong laser light rapidly heats up a certain spot on the disc,
when it cools its crystalline structure becomes amorphous. When
the spot is slowly heated by a weaker laser it changes back to its
crystalline structure after it cools. Since the light reflection ratios
of the crystalline and amorphous structures are different, the ‘0’
and ‘1’ of digital data can be represented on the disc. Re-writable
discs make use of this phase modulation technique to allow re-
recording over previously recorded content.
Differences in disc side construction
The physical format of commercial DVD-Video software and
other playback-only DVD discs has a continuous line of recorded
pits on the disc, just like CD-ROM. By reading these pits
optically, the disc can be played back.
Chapter 2
Features of Recordable
DVD Formats
Recordable DVD operates through a combination of
three format layers: the physical format, the logical
format and the application format.
RDR-GX7 Technical Notes
5
Application format (language)
Logical format (lines on the paper)
Physical format (the paper itself)
The three format layers of DVD
Recording layer
Reflecting layer
Playback Recording
Playback of spot changed
by the recording laser
Laser
Playback of spot not changed
by the recording laser
Optical pickup
Comparison of laser output
During recording
During playback
Causing chemical change in organic dyes on
recordable discs
During recording
Playback Recording Erasing
Amorphous structure Crystalline structure
Laser
Optical pickup Comparison of laser output
Since the shape and light
reflection ratio for the
amorphous and the
crystalline structures differ,
the 0 and 1 of digital data
can be represented.
Recording layer
Using the phase change of recording material in
re-recordable discs