CD-RW is a rewritable compact disc; the acronym stands for the English expression Compact Disc ReWritable.
The first CD -RW came in 1996 on the market - by Philips, Sony, Hewlett -Packard, Mitsubishi Chemical and Ricoh - and could only store 650 MB. As of 1998, a greater storage capacity of 700 MB is possible. Due to many limitations, such as speed, data security and storage capacity of CD -RW has remained a niche application.
This rewritable media can be described up to 100,000 times new with suitable writing instrument according to manufacturer's instructions. The technique of CD-RW is based on phase change technology, therefore, a reflectance of 15 to 25 percent is achieved. The properties of the medium and the Schreib-/Löschvorgang are defined in the Orange Book Part III.
A CD-RW medium has, in principle, the same layers as a CD-R medium. However, the reflective layer is a silver -indium- antimony -tellurium alloy, which has a polycrystalline structure and reflecting properties in the original state. When writing the write beam uses its maximum power and the material is heated to 500 to 700 degrees Celsius. This leads to liquefaction of the material. In this state, the alloy loses its polycrystalline structure assumes an amorphous state and loses its reflectivity. The polycrystalline state of the volume forms the trenches, the amorphous surveys. The sample signal thus read out is not caused by the extinction or amplification of the laser light through superimposing of the reflected light with the emitted as pressed discs, but as writable CDs of given or not given (or weaker ) reflection of the laser beam. For deletion of the data carrier the write beam heats the amorphous regions with low power to about 200 degrees Celsius. The alloy is not liquefied, but returns to the polycrystalline state and is thus again able to reflection.
On a CD- RW data can be added later in another session. But this is only possible if the disc has not yet been completed. The data of the fired session can be changed in principle. The following session can only replace existing data or mark as deleted.
Since CD-RW discs are often described with confidential data, ensure that the CD - RW discs can be safely deleted if necessary. The Federal Office for Security in Information Technology distinguishes between conservation objectives and advises accordingly to the following actions:
- In normal protection requirements overwritten with arbitrary data and a means of destruction paper shredders ranges ( maximum size of the fragments 200 mm ²)
- At higher protection requirements are advised to destroy the disk. The fragments having to be less than 10 mm ². In a thermal destruction of the media to be heated to about 300 ° C for at least 60 minutes.
Older CD -ROM drives ( before 1997 or Rule of thumb: less than 24 -fold), a CD - RW disc can not be read as a rule, the same applies to some CD players and changers with a construction date before 2005 (especially in the car radio range). Drives that can burn CD -RW, can usually also burn CD -Rs. Since 2003, CD -RW drives are increasingly being replaced by DVD burner that can read through their backward compatibility, CD -RW and write.
The file system also the UDF comes with the CD -RW in addition to the ISO 9660 file system of the CD -ROM for use. Since version 1.5 UDF packet by packet writing is supported, which allows a hard disk-type use.
A CD - RW media can not be described other than CD - Rs in any CD -RW drive, depending on the specified speed range. There are media for 1 - to 4- times the write speed, which can be burned by the speed with up to 4 -fold speed dependent on any CD -RW burner. These blanks can wear the English name " multi-speed ", "Normal Speed" or " Low Speed". Furthermore, there are so-called high-speed media once for 4 - to 10 -fold - and on the other for 4 - to 12 - fold speed, ultra - speed media for 10 - to 24 - fold speed and Ultra Speed media for 16 - to 32 times the speed, this, however, suitable burners are necessary. You can see the torch to the higher maximum write speed for CD - RWs, and to the right upended next to the Compact Disc logo lettering High Speed, Ultra Speed and Ultra Speed . While Ultra Speed burner can burn to all of these media their respective maximum speed, only high-speed and normal media remain at high speed burners for burning. Readable but the media mentioned are in any multi-read -enabled, that is capable of reading CD-RW, CD-ROM drive, the distinctions apply only to the burner during the firing process.