Optical disc authoring
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In computing, optical disc authoring, including DVD authoring, known often as burning, is the process of recording source material—video, audio or other data—onto an optical disc (compact disc or DVD).
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[edit] Process
To create an optical disc, one usually first creates a disk image with a full file system designed for the optical disc, and then burns the image to the disc. The disc image is a single file, built and stored on the hard drive, which contains the entire information to be contained on the disc.
Many programs create the disc image and burn in one bundled operation, so that end-users often do not know the distinction. However, a useful motivation for learning this distinction is that creating the disc image is an "expensive" (time-consuming) process. Most disc writing applications will silently delete this image from the "temporary directory" in which it was built unless users instruct the disc burning application to preserve the image, which can then be used for creating further copies of the same image without the need to rebuild the image each time.
There are also packet-writing applications that do not require writing the entire disc at once, but allow writing parts at a time, allowing the disc to be used in the same way as rewritable media such as floppy disk.
There exist many optical disc authoring technologies for optimizing the authoring process and preventing errors. Discs whose burn failed are colloquially termed coasters since that is all they are good for.
Some operating systems are aware of disc images as a filesystem type, and can mount these images so that they appear as actual mounted discs. This feature can be useful for testing a disc image after authoring but before writing to the disc media.
[edit] Sessions
Data on an optical disc is laid out in sessions. Each session consists of a lead-in, containing the session's Table of Contents, the program area in which the individual tracks are located, and the lead-out.
The number of tracks is limited to 99 in a session. The specifications require at least one track in each session. The tracks are located in the program area of the session.
In multisession discs, the lead-in areas contain addresses of the previous sessions. The TOC written in the lead-in of the latest session is used to access the tracks.
[edit] TOC
The Table of Contents (TOC) is the area where the layout of the tracks on the disc is described. It is located in the lead-in area of the disc session. The TOC on discs is in principle similar to partition table on hard drives.
Nonstandard or corrupted TOC records are abused as a form of CD/DVD copy protection, in e.g. the key2audio scheme.
[edit] Lead-In
The lead-in area of a CD session is the starting part of the disc. It contains the TOC for the session, and the address of the next available free part of the disc available for the start of the next session, unless the disc is closed and therefore no more sessions can be added, or the disc is not multisession.
[edit] Lead-Out
The lead-out area is the ending part of the CD session. When the session is closed, the lead-out area is written.
The first lead-out is 6750 sectors (about 13 megabytes) long, each subsequent lead-out is 2250 sectors (4 megabytes) long.
[edit] Tracks
A track is a consecutive set of sectors on the disc containing a block of data. One session may contain one or more tracks of the same or different types. There are several kinds of tracks: Audio tracks, Data tracks.
[edit] Hardware
Authoring is commonly done in software on computers with optical disc recorders. There are, however, stand-alone devices like personal video recorders which can also author and record discs.
[edit] Software
Use of optical disc recorders require optical disc authoring software, (sometimes called "burning applications" or "burner applications"). Such software is usually sold with the recorder.
[edit] File systems
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Optical disk file systems include ISO-9660 (often known simply as "ISO") and Universal Disk Format (UDF). ISO is most common for CDs and UDF is most common for DVDs.
[edit] ISO 9660
ISO 9660 is a format mainly used on CDs. The ISO 9660 can be extended with Joliet, Rock Ridge, Amiga Extensions to Rock Ridge, El Torito, or the Apple ISO9660 Extensions. The Joliet file system was made by Microsoft. It makes it possible to have long file names, among other things. Rock Ridge is a system providing ownership, fewer restrictions on the file names, and more. Amiga extensions allow use of Amiga attribute bits and comments. El Torito makes it possible to boot from a CD. The Apple Extensions enables creator codes, file type, on so on.
[edit] Universal Disk Format
Universal Disk Format is a format. UDF can be extended with Mount Rainier which makes it possible to use the disc like a floppy. You can delete, create, modify files, without having to write the whole disc again.
