coupled with more economical CD-R discs, led to abandoning the format. Other magneto-optical media, unbound by limitations of the typical CD-ROM filesystems, replaced the CD-MO. Mechanism of action Rewritable media can, with suitable hardware, be re-written up to . The CD-RW is based on phase change technology, with a degree of reflection at , compared to for CD-R discs. The properties of the medium and the write and erase procedure is defined in the Orange Book Part III. To maintain a precise rotation speed, tracks have a slight superimposed sinusoidal excursion of at a frequency of . In addition a frequency modulation is applied to provide the recorder with an absolute time reference. Groove width is and pitch of . The media for CD-RW has the same layers as CD-R media. The reflective layer is, however, a silver-indium-antimony-tellurium (AgInSbTe) alloy with a polycrystalline structure and reflective properties in its original state. When writing the laser beam uses its maximum power () to heat the material to causing material liquefaction. In this state, the alloy loses its polycrystalline structure and reflectivity and assumes an amorphous state. The lost reflectivity serves the same function as bumps on manufactured CDs and the opaque spots on a CD-R are read as a 0. The polycrystalline state of the disc forms the trenches, which are read as 1. The scanning signal when reading is created by strong or weak reflection of the laser beam. To erase the disc, the write beam heats the amorphous regions with low power to about . The alloy is not melted, but returns to the polycrystalline state and is again reflective. Authoring During and after a disc authoring the distribution of data on the CD-RW varies. The following areas are present: PCA: The Power Calibration Area is used to determine the correct power level for the laser. PMA: The Program Memory Area of a CD-RW is a record of the data recorded on an unfinished or unfinalized disc. It is used as a transition TOC while the session is still open. PMA records may contain information on up to 99 audio tracks and their start and stop times (CD-DA), or sector addresses for the start of data files for each session on a data CD. PA: The Program Area contains the audio tracks or data files. SUA: The System User Area The PCA and the PMA grouped together are sometimes