CD-RW
| Storage medium Compact Disc ReWritable (CD-RW)
|
|
 CD-RW logo |
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| General | |
|---|---|
| Type | optically |
| capacity | 650 MB / 74 min. (Outdated) 700 MB / 80 min. 210 MB / 24 min. ( Mini-CD ) |
| size | 12 cm × 1.2 mm 8 cm × 1.2 mm (mini CD) |
| origin | |
| Launch | 1997 |
| successor | DVD -RW, DVD + RW |
CD-RW is a rewritable compact disc ; the abbreviation stands for the English expression C ompact D isc R e W ritable .
The first CD-RWs came on the market in 1997 - from Philips , Sony , Hewlett-Packard , Mitsubishi Chemical and Ricoh - and could only store 650 MB. From 1998 a larger storage capacity of 700 MB is also possible. Due to many limitations, such as speed, data security and storage capacity, CD-RW has remained a niche application.
functionality
These rewritable data carriers can be rewritten up to 100,000 times with suitable writing devices according to the manufacturer's instructions. The CD-RW technology is based on phase change technology , so a degree of reflection of only 15 to 25 percent is achieved. The properties of the medium and the write / delete process 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 in its original state has a polycrystalline structure and reflective properties. When writing, the writing beam uses its maximum power and heats the material to 500 to 700 degrees Celsius. This leads to a liquefaction of the material. In this state, the alloy loses its polycrystalline structure, becomes amorphous, and loses its reflectivity. The polycrystalline state of the data carrier forms the trenches , the amorphous state the bumps. The scanning signal during reading is not created by extinction or amplification of the LASER light by superimposing the reflected light with the emitted light, as in the case of pressed CDs, but rather, as in the case of recordable CDs, by given or not given (or weaker) reflection of the LASER beam. To erase the data carrier, the write beam heats the amorphous areas with low power to around 200 degrees Celsius. The alloy is not liquefied, but returns to the polycrystalline state and thus becomes reflective again.
Multisessions
Data can also be added to a CD-RW later in another session . However, this is only possible if the CD has not yet been finalized . The data of the burned session can in principle be changed. The following session can only replace existing data or mark it as deleted.
Secure deletion
Since CD-RWs are often written with confidential data, it must be ensured that the CD-RWs can be safely erased if necessary. The Federal Office for Information Security distinguishes between protection goals and advises the following measures accordingly:
- With normal protection requirements, it is sufficient to overwrite with any data or to destroy it using a document shredder (maximum size of the fragments 200 mm²)
- If there is a higher protection requirement, it is advisable to destroy the data carrier. The fragments must be smaller than 10 mm². In the event of thermal destruction, the data carriers should be heated to over 300 ° C for at least 60 minutes.
compatibility
Older CD-ROM drives (before 1997 or rule of thumb: less than 24x) can usually not read a CD-RW medium, the same applies to some CD players and changers with a build date before 2005 (especially in the car radio sector ) . Drives that can burn CD-RWs can usually burn CD-Rs too . Since 2003, CD-RW drives have been increasingly replaced by DVD burners , which, thanks to their downward compatibility, can also read and write CD-RWs.
In addition to the ISO-9660 file system of the CD-ROM, the UDF is also used as the file system for the CD-RW . Since version UDF 1.5, writing in packages has been supported, which allows hard disk-like use.
| Writing speed | engl. designation |
|---|---|
| 1-4 × | Multi-speed, normal speed, low speed |
| 4-10x | High speed |
| 4-12 × | High-speed + |
| 10-24x | Ultra speed |
| 16-32x | Ultra Speed + |
Unlike CD-Rs, a CD-RW medium can not be written to in every CD-RW burner , depending on the specified speed range . There are media for 1–4 times the writing speed, which can be burned in any CD-RW burner at a maximum of 4 times the speed, depending on its speed. These blanks can be called "Multi-Speed", "Normal Speed" or "Low Speed". There are also so-called high-speed media for 4 to 10 times the speed - and for 4 to 12 times the speed on the other hand, ultra-speed media for 10 to 24 times the speed and ultra-speed + media for 16- up to 32 times the speed, but suitable torches are required for this. The burners can be recognized by the higher maximum writing speed for CD-RWs and by the lettering High Speed , Ultra Speed or Ultra Speed + on the right side next to the Compact Disc logo . While Ultra-Speed + burners can burn their respective maximum speeds on all of the media mentioned, only high-speed and normal media remain for burning with high-speed burners. However, the media mentioned can be read in any MultiRead- enabled, i. H. CD-RW readable CD drive, the distinctions only apply to the burner during the burning process. Ultra-speed media has been hard to find since the mid-2010s.
See also
Individual evidence
- ^ The history of the CD - The CD family - Research | Philips . In: Philips . ( philips.com [accessed November 23, 2017]).
- ↑ Selection of suitable procedures for the deletion or destruction of data. (No longer available online.) Formerly in the original ; Retrieved February 23, 2011 . ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
