CD-ROM (Compact Disc Read Only Memory)
compact discs were introduced into the audio market for the first time in 1980 by the hand of Philips and Sony as an alternative to vinyl and the cassette. Later readers were designed to fit in the computers. Since its inception, has evolved primarily in reading speed, so that the first reader was followed by another called 2x, which as the name indicates double the speed of reading data. Was followed 6x, 8x, 10x, 12x, 16x, 24x, 32x, 36x, 40x, 48x, 50x, 52x, 54x and 56x
DVD-ROM (Digital Video Disk Read Only Memory)
Sony in September 1995 , along with nine other companies (Philips, Mashusita, Toshiba, ...) joined forces and created a unified standard for the DVD format, much more capacity than the CD. Reading speeds work just like the CD, is taken as the first reader who appeared and this has increased to X16.
CD RECORDER breeding units of CD-R and CD-RW have a laser that is only 1 inch of the CD. This laser is used to mark the disk surface, brands such as pits and lands. The brands are arranged inside the CD from the inside to the outside through a concentric spiral.
The CD-R uses storage type WORM (Write Once Read Many), which means "write once, read many." It consists of polycarbonate, an organic layer (usually cyanine), a reflective layer (usually gold or silver alloy) and a final protective layer.
In this case, the recorder's laser acts on the surface of the organic layer marking the pits. This layer is discolored and bulging in these areas. The pits appear to be part of this organic layer become unstable and reflective (due to heat). The CD player passes through the polycarbonate layer and the organic, reflecting on the reflective layer. When it comes to a bulge is a change in the reflection, so that is interpreted as a 1. A CD-R can not be overwritten.
A disc-rewritable (CDRW), the structure of the layers is different about a CD-R. Like CD-R is composed of the polycarbonate layer and a protective top layer. It differs in the recording layer, composed of a mixture of different components, such as tellurium, selenium and germanium. This layer is protected by two others that reinforce the perspective and control their cooling. The important thing of this system is that due to laser heating and subsequent cooling, this intermediate layer can be purchased at certain points in an amorphous state with irregular structure (which corresponds to the pits), or maintain a crystal structure with stable and regular structure (lands .)
When we need to erase a CD-RW, up to a laser with a lower temperature than the irregular structure returned back to a polycrystalline, leaving the CD-RW ready to be burned again. The number of rewrites is estimated at 10,000 but this figure, in practice, it is highly unreliable.
As in the previous case, when done reading the CD-RW, the laser affects the middle layer and reflect changes in going from the crystalline to the amorphous layer. These changes are coded as zeros and ones, and stored as information.
A section to be considered on a tape recorder is the size of buffer, this buffer is a memory that carries the recorder to store data sent from the PC before burning, the size varies between 2 MB and 8 MB buffer, the larger logically less likely to fail the recording there.
DVD RECORDER
In that operation is very similar to burning a CD, but the pit size is smaller and with other factors such as type of material used and the laser is more precise, high capacities are obtained from these compared to the CD. There are now on the market dual-layer DVDs (in many cases will see its abbreviation => DL = Double Layer = Double Layer, DVD = DVD DL Dual Layer) which allows stacking 2 layers and thus achieve a higher capacity, we can even find DVDs that employ the 2 sides.
The writing speed depends on what is recorded and that kind of support. It is slower to burn to a rewritable (either CD or DVD) CD / DVD Write Once. Here is the long table and reading speeds of writing as each supported by a Pioneer DVD recorder Modern: http://www.pioneer.eu/eur/products/45/104/442/DVR-212BK/index.html
The next step in evolution is unclear today, there are 2 formats that are competing to be the next standard: Blu-ray up to 50GB (designed by Sony) and HD-DVD's 30GB (designed by Toshiba).
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