One of the technologies most used in the world of computing is the recording of CDS, whether data are of music. With the popularization of the devices, recorders, CD’s (a consequence the reduction of costs) this habit is each more and more common. This article aims to show how to work the CD’s recordable and rewritable (CD-R and CD-RW).
The CD media
In the market, there are two different types of CD’s (media) with which it is possible to burn data and music CD-R (Compact Disc – Recordable) CD-RW (Compact Disc – Recordable Rewritable). The first allows data to be recorded on a CD only a single time, not being able to change or delete information. The second allows you to record and re-record a CD, deleting and adding data again. What causes the difference among these types of CDS is the material used by them. The CD-R uses a type of material that when burned by the laser of the CD recorder suffers a transformation that does not allow to change it, leaving the media such as a CD-ROM common. Already the CD-RW uses a material of the type phase-change (phase shift), which consists of a kind of particle that suffers the action of the laser of the recorder to store data and then can suffer another action to return to the original state, and allow that information to be written again. Below, see how they are mounted to the CD-R’s and the CD-RW’s.
The CD media are made up of layers. The the material used in them is the color of the media (silver,golden, blue, green, etc.). In the case of CD-R are used, basically, five layers:
Layer 1: surface-protection – layer used to protect the recorded data, as a sort of “cover protective”. Media very cheap (low quality) not always have this material;
Layer 2: laqueamento – also has the function to protect the data, getting it just below the layer of protection and serve as a complement to this. Thus, the media cheap also can not have this layer;
Layer, 3: reflective layer – as the name indicates, this layer is responsible for reflecting the laser beam emitted by the cannon of the instrument the recorder. According to the laser intensity, the layer of recording (explained below) changes that characterize the recording of the data;
Layer 4: layer recording – the reflection coming from the layer 3 burning this part forming the variable changes in the material, which constitute the data stored on the media;
Layer 5: the base plastic is a layer of polycarbonate, that forms the basis for the entire CD. With a thickness of 1.2 mm, such a layer is the more thick and is formed as a espirial.
e CD-RW has 6 layers and replaces the reflective layers and recording by a material able to change its shape through the application heat, allowing rewriting of data. Its color is a little darker than the silver of the CD common:
Layer 1: surface of protection – has a protect the recorded data;
Layer 2: laqueamento – also has the function to protect the data, getting it just below the layer of protection and serve as a complement to this;
Layer 3: layer dielectric – coating the recording layer layer (4) removing excess heat during the recording process;
Layer 4: recording layer – consists of a material mixing silver, antimony, and tellurium. Through the heat emitted by the laser cannon of the apparatus recorder, the data are recorded in this layer. At a given temperature, this layer back to its normal state. Through a low temperature is that the apparatus reading the recorded data;
Layer 5: layer-dielectric – same as layer 3, with the difference of staying below the recording layer;
Layer 6: plastic base – is a layer of polycarbonate, that forms the basis for the entire CD. With a thickness of 1.2 mm, such a layer is the more thick and is formed as a espirial.
The packaging of the media of CD-R and CD-RW discs generally have information helpful but that not every user knows what it means. A this information may be like this: 650 MB/74min or 700 MB/80 min. This means that the CD has 650 (or 700) MB of capacity storage of data and which is used for recording audio, features 74 (or 80) minutes of capacity.
On the CD-R a other information that appears can be in the format 1X – 16X, which means that the CD can be written in any instrument recorder which rotate in a speed range that goes from 1X to 16X. In the case of the CD-RW drive, the first X indicates the speed of rewriting, while the second X indicates the recording speed. Thus, if for example the packaging indicates 4X-10X means that the recording it is made in to 10X while the rewrite is done in 4X. A X is equivalent to 150 KB per second.