Disc-at-once

from Wikipedia, the free encyclopedia

Disc-At-Once ( DAO ) is a general term for a group of writing methods with which an entire CD or DVD including lead-in and lead-out (beginning and end area) can be written without switching the laser off or on again adjust. Of the writing methods mentioned in the MMC standard, SAO and RAW fall into the group of DAO writing methods.

The advantages are that pauses or gaps (“pregap”, index 0 ) between tracks can be set to values ​​that are not permitted in the standard. However, not all drives allow the length of the index 0 to be set to any value in SAO mode. Since in RAW mode the drive does not evaluate what is being burned, any index 0 length is possible on all drives that support RAW mode.

RAW

At raw , engl. for 'unprocessed', 'raw', without a CD resp. DVD format worked. In RAW mode, for example, a CD is written in portions, for example as a memory image, into a file or written from this onto the data carrier from a memory image file without evaluating or changing the format of the data.

RAW is the only write mode with which it is possible to write RW subchannel , CD-Text and ISRC information, catalog numbers, CD + MIDI , gaps, indices and manipulated TOCs . There are three different RAW modes:

  • RAW 16 writes PQ (16 bytes) subchannel. 2 bytes of CRC data in the Q channel are generated by the burner.
  • RAW 96P writes PW (96 bytes) subchannel, but 2 bytes of CRC data are generated by the burner in the Q channel. This mode is rarely used in practice and is supported by a few burners.
  • RAW 96R writes PW (96 bytes) subchannel. This is the best mode and allows all subchannel information to be written.

This additional data of the subchannel is relevant for extended functions such as CD-Text, but also for copy protection mechanisms. Paradoxically, in these modes it is possible for the writer to write data that it cannot read; Formats such as CD-Text or CD + G can also be duplicated, even if the recorder basically does not support these formats. To do this, the data must have been correctly read in beforehand, e.g. B. using another drive.

In RAW mode, a multi-session CD can theoretically be written to in one go. However, since there is no known burning program that supports RAW mode and that can write a Program Memory Area ( PMA ), a write prefix, in RAW mode, such CDs cannot be continued and are even recognized by Philips burners as defective and illegible.

SAO

In session-at-once mode (SAO), the data is also written to the medium without switching off the laser; however, a so-called B0 pointer can be set and the drive also writes a PMA in this case (albeit with a write interruption) in front of the lead-in. This way, further sessions can be added. This is z. B. used with CD-Extra .

Web links