Freyja

A rewriteable compact disk (or CD-RW, for Compact Disc ReWritable ) is a Compact disk, on which one can write and rewrite up to 1000 times of the computer data or audio, however the manufacturers often guarantee between 1000 and 2000 writings.

A CD-RW can contain approximately 650 or 700 Mégaoctet S of data on a medium CD-RW, and this for an unlimited number of writings, contrary to CD-R.

The “Universal Disk Format” in its version 1.5 described a Filesystem which allows a random writing, but its use limits the size useful of the disc for approximately 530 Mo.

Technology

The reflective layer out of aluminum of the preregistered compact disks standard is printed in a permanent way. Discs CD-RW have a layer of recording to phase shift and an additional reflective layer of money/aluminum.

A laser beam can dissolve the crystals in the layer of recording and to put them in a noncrystalline amorphous phase or to make them undergo slow reheats at a lower temperature until they find a crystalline state. The respective reflections of the various surfaces reveal them in hollow or bumps as in standard CD.

Readers

The readers and media CD-RW are more expensive than their counterparts CD-R. CD-R is sometimes regarded as a better technology for filing, because the data cannot be modified or faded in an accidental way, and encourage a better policy of storage.

Media CD-RW cannot be read on readers of cédéroms manufactured before 1997 because of their reduced reflectivity (15% against 70%).

The majority of readers CD-RW can also write on a medium CD-R , but this writing is final. Put aside the possibility of completely erasing the contents of a disc, the CD-RW are similar to CD-R S and are prone to the same restrictions; i.e. they can be wide, but not rewritten in a selective way, and must be “closed” before being able to be read in a normal reader of Cédérom S (order with the software of engraving to put on CD information which means that there are no more files on standby of engraving). A variation of the formatting UDF makes it possible the CD-RW to be read and written in direct manner, but limit the capacity with 500 Mo.

Standards on speeds of engraving

The CD-RW can each one be written at various speeds; in the same way each engraver has his own capacities with regard to speeds of writing. To be able to engrave a CD-RW, speeds of this CD-RW must correspondrent with those of the engraver.

Standards were create in order to easily be able to distinguish the capacities from each one:

Generally, the standard is indicated on the not-inscribable face of the CD-RW like on the drawer located on the front face of the engraver.

See too

Data storage | Material (data processing) | Cédérom | CD-R

External bonds

Understanding CD-R & CD-RW by Hugh Bennett
FAQ CD-R

This article is mainly based on material coming from a translation of Free On-line Dictionary off Computing and is used with permission according to GFDL.

Simple: CD-RW

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