The data on a disk is written in sessions. Each session consists of a lead-in, containing the table of contents, the area in which data is written, and the lead-out.
The maximum number of tracks for CD (not intended as music tracks, ie detached tracks) is 99. For each session one track must be written. The tracks are located in the part where the data is written.
In multisession discs, the lead-in areas contain the memory address of the end of the last session. The table of contents are written in the last session to gain access to the tracks.
Table of Contents
The table of contents is the area where the location of the data is written to the disk. It is located in the beginning of the disk and has the same function as the partition table on a hard disk.
In the diagrams key2Audio damage or abnormal writing TdC is used (and abused) as a protection for copying CDs.
The lead-in area of a CD is in the initial part of the support. It contains the TdC, and the memory address of the next free space to start the CD, unless the disc is not closed or is not multisession.
A trace is a continuation of sectors on a disc containing data. Each session can contain one or more tracks, both data and audio.
The area of Lead-OUT is located at the end of the session on a disc. The area of Lead-OUT is written when the session has finished burning the disc. The first Lead-OUT occupies about 13 MB, each sector of Lead-OUT following occupies 4 MB.
Burning can be done on a computer with a CD burner or other CD burning appliance. There are stand-alone devices such as video cameras that can also be used as external burners.
To burn optical discs, appropriate burning programs are required. Within many modern operating systems, including Windows XP and Vista, some Linux distributions and Mac OS X implements a feature to burn CDs without resorting to third-party software.
The file systems for hardware are: ISO-9660 (also called simply “ISO”) and Universal Disk Format (UDF). The ISO format is more common for CD, while the UDF is for DVDs.
ISO 9660 is a format mainly used on CDs. The ISO 9660 can be extended to Joliet, Rock Ridge Extensions for Amiga Rock Ridge, El Torito, or extensions Apple ISO9660. The Joliet file system was created by Microsoft.
With this type of FS is possible to have names that exceed the normal threshold. Rock Ridge is instead a FS owner, with more restrictions on names, and more.
Amiga extensions allow the use of attributes and comments for Amiga computers. El Torito bootable CD creates, while the Apple extensions allow you to change names, files, etc..
The UDF provides file names with upper and lower case, with a maximum length of 255 characters. It has been optimized for use with large data and to minimize the need for changes when a file needs to be added or deleted – for this reason it is used by certain CD-R/CD-RW writing software packages.