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A pressed CD is made up of three areas of information:
- The LIA, or Lead-in Area, which extends for a radius of 23-25 mm and which is used for engraving the CD’s “table of contents” (and so is called the TOC) defines the start and end positions of tracks and files on a disc.
- The Program Area which extends from a 25 mm to 58 mm radius is the area containing the audio, video or computer data.
- The Lead-Out Area is burned after the program area and constitutes a buffer zone containing no data and completing the disc. It must be at least 0.5 mm wide. As a minimum it contains the equivalent of 90 seconds of silence at minimum speed (1X).
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A CD-R with more than the three areas described above contains an area called the SUA (System User Area) which is sub-divided into:
- a PCA or Power Calibration Area which corresponds to a test zone which allows the laser to adapt its power to the type of media in the recorder. Actually, CD-Rs can be manufactured from various thermo-sensitive chemical compounds, each with their own reflective characteristics. With each calibration attempt, the recorder registers that it has carried out a test. After 99 calibration tests per media, the recorder indicates that the media is not readable or not compatible.
- a PMA (Program Memory Area) which contains the TOC until the disc is closed. When the disc is closed, the TOC is recorded in the lead-in area. Only recorders can access the PMA area, the reason why a standard player cannot read an unclosed disc.
- When you record a CD in multi-session mode, a lead-in is created with each session. The last one points to the TOC of the previous session and so on. A chain is therefore created between the lead-ins which can lead to the following type of error message:
- The reader can only read the data for the last session.
- The reader can only read the data for the first session.
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