The more advanced DVD players are capable of playing back a wide range of drives, besides just DVDs. The DVD players can play back DVD RAM, DVD-R, DVD-RW, DVD+R, DVD+RW, CD audio, CD-R, CD-RW, MP3, WMA, JPEG, MPEG 4, VCR, picture CD, SVCD, DVCD, and DivX. These DVD players are available with various features and a wide price range. The DVD players manufacturers decide upon the types of features to incorporate and the type of discs that are supported, taking into account consumer demands and affordability. Region free DVD players are generally designed to read all the various discs and are therefore higher priced in the market. They are widely available in all the Region 2 countries including UK, France, Italy, Greece, and Spain. In these countries, it is legal to own and use region free DVD players if used for non-commercial purpose. CD-R There are two types of CDs, the CD-R and the CD-RW. CD-R (Compact Disc-Recordable) is a variation of the digital audio disc and was invented by Philips and Sony, in 1988. The CD-Rs were first produced by the companies Taiyo Yuden, Kodak, Maxell, and TDK. They are capable of storing music or data. The CD-R is burned using laser. The standard CD-R is a polycarbonate disc of 120mm or 80 mm diameter and a 1.2 mm thickness. These standard CD-Rs have a storage capacity of 74 minutes of audio or 650 MB (Mega Byte) of data. The non-standard CD-Rs can store 702 MB data and 79 minutes and 59 seconds of audio. The writable surface of the CD-R has a spiral groove, which guides the laser beam for writing and reading information. The spiral groove side is coated with a thin layer of organic dye, followed by a thin layer of silver, a silver alloy, or gold. Then a final protective layer of lacquer, which is photo-polymerizable, is coated as a thin layer, and is cured using UV light in the end. This is how a blank disc is prepared. The data is inscribed on the spiral groove. For writing data on a CD-R, the laser physically burns the organic dye by heating to a certain level. This area on the disc that has been written upon turns opaque to the laser and reflects less light than the other areas. When a CD-R is written upon, its organic dye undergoes an irreversible decomposition. Hence once a CD-R is written upon, it is permanent and cannot be erased or re-used. Three Methods for Writing on a CD-R using a CD Recorder There are three methods used for writing on a CD-R using a CD recorder. In the Disc At Once technique, the CD is written completely in one go, and thereafter Closed, such that no more data can be added to it subsequently. This type of recording is commonly utilized in Live audio recordings. This CD-R becomes a read-only CD. The Track At Once technique is used for recording one track at a time, leaving the CD-R open for further additions subsequently. These CDs are capable of storing both data and audio. The third technique is the Packet Writing system in which the data is recorded as appendages, allowing for new data to be added later. These CD-Rs are very similar in functioning to CD-RWs. However, due to this technique, certain DVD players are unable to read these CD-Rs. CD-RW A CD-RW or Compact Disc Re Writable, as the name suggests, is a CD disc on which data can be written, erased, and rewritten. A CD-RW is capable of re-writing as many as 1,000 to 100,000 times, depending on the type of disc. A CD-RW is also capable of erasing single files at a time. The CD-RW is similar to the CD-R in most of the recording and usage aspects. These are compatible for Disc At Once and Packet Writing just like the CD-R. The CD-RW discs are written using the technology of Phase-Change. When written upon, the laser alters the physical state of the writable layer from crystalline phase to the amorphous phase. The refractive index of the crystalline form differs from that of the amorphous form and makes the disc optically readable. Multi Read and Multi Play The CD-R and CD-RW can be played back conveniently on the CD players. There are a number of DVD players that can play only DVD discs and are incapable of reading the CDs. This is due to certain technological disparities between the two formats. The CD-R, CD-RW, and DVDs are read using different laser specifications. The CD-R is read using infrared 780nm laser, while the DVD is read by a visible red 635nm or 650nm laser. The CD-RW can be read by the 650nm laser, since its recording layer is not very dependant on the laser wavelength for being read. Also, the optical device used for reading DVDs has a numerical aperture of 0.60 as opposed to 0.45 used for CD-R. So, certain DVD players cannot read CD-R discs and need to be fitted with a dual laser to be able to read CD-Rs also. Most DVD players are capable of reading CD-RW, but in some cases, the optical system of the DVD is not sensitive enough to read the signal change and lower reflectivity of a CD-RW. The consumers usually demand DVD systems that are capable of handling all types of discs. The DVD players were modified to be able to read and play other discs by incorporating the MultiRead and MultiPlay features. This is possible by the addition of an extra laser optical pickup that generates both types of wavelengths. The MultiRead format was created in 1997 by OSTA. This was devised to link together the CD and DVD technologies, and enable the DVD players to read CD-R and CD-RW discs. The OSTA formulated MultiPlay in 2000, to enable the CD and DVD electronic devices to be compatible with CD-R and CD-RW devices. Thereafter, the MultiRead and MultiPlay compliant DVD players and recorders are able to play both CD-R and CD-RW discs. Most of the compliant DVD devices provide a MultiRead and MultiPlay logo sticker on the box to be recognized by the consumer. |
