Groove wobbling
 
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generation of a spindle motor control signal
 
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generation of a gate signal used in detection of the land pre-pits

Land pre-pits
 
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high-precision positioning when writing data
 
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acquisition of recording address and other information necessary for recording

The combination of these two features provides a high precision, highly reliable pre-format.
This pre-format signal is obtained through differential detection of the laser light reflected from the disc during tracking, but is designed so as not to be detected in the overall signal ordinarily used to obtain user data from an optical disc. That is, the pre-format signal used during recording is designed so that it has no effect on the playback of data the user has recorded to the grooves.
Figure 4 shows a basic diagram of the detected signal. As seen in the figure, the groove wobble signal is detected as a sine wave, while the land pre-pit signal is coincident with the first three peaks of the wobble signal in each synch frame (an odd or even frame). These three pulses make up one set. These three pits are assigned in a fixed pattern. The first bit always exists, and the sync pattern in the recorded data is synchronized with this pre-pit. This method of recording user data while providing phase compensation to the recording clock based on the pre-pit position makes it possible to append data or write data with much greater precision than is possible with CD-R and similar format.
Today, there are three types of linking loss area (the loss of user data which accompanies appending or rewriting of data), with magnitudes of 32 kB, 2 kB, and 0 bytes. Use of the above-described method makes it possible to do "lossless linking" (in DVD-R for General and DVD-RW).

6.3.2 Write strategy

As one means of increasing recording performance when actually writing a signal to the disc, the DVD-R and DVD-RW specifications define a type of laser output multi-pulse modulation called write strategy, which rely on the fact that DVD-R and DVD-RW use heat for recording. Figure 5 shows the basic write strategy for these two types of disc. For both media types, the laser pulse for a single recording mark is divided into a top pulse and a series of multiple pulses, which provides control of distribution of heat generated in forming the mark. DVD-R uses two levels of laser power, while DVD-RW uses three levels to enable overwriting. For the latter in particular, the series of pulses is ended with a cooling pulse.
This method alleviates heat interference between adjacent and the heat accumulation at the trailing edge of the formed mark, and makes it possible to obtain a playback signal with good characteristics.
The DVD-R and DVD-RW specifications also provide the option of encoding the optimal pulse width for a particular media type and embedding that information in the land pre-pit, as a mechanism for further increasing system margin.

Figure 5 Write Strategy

IV.Features of the Specifications

As mentioned above, the 4.7 GB DVD-R specification was divided and published as two specifications (DVD-R for Authoring version 2.0 and DVD-R for General version 2.0), out of concern for copy protection issues. The former specification is restricted to professional authoring applications, while the latter specification is available for general consumer applications. The DVD-RW specification was also designed for consumer applications, and was revised from version 1.0 to version 1.1 to perfect its copy control mechanisms. At the same time, playback compatibility with DVD-ROM was also improved.