DVDs have become a common storage medium for computer users owing to their portability, cost and storage space. A DVD burner will allow you to back up your data as well as make video discs to play in regular DVD players. If you have an application that requires regular use of recorded DVDs, however, you may be able to save money using rewritable media instead. Rewritable DVDs offer all the benefits of a recordable disc coupled with the ability to reuse the same disc many times.
All DVDs contain a thin layer of foil sandwiched between plastic layers. In the case of a manufactured DVD, this foil is "pressed," creating small pits that alter the reflection of a laser beam as it passes over the surface. These alterations create the binary ones and zeroes that allow the disc to store data. Recordable DVDs use a layer of heat-sensitive dye instead, which discolors as it is heated. This creates permanent dark spots that block the laser's reflection, storing data in much the same way as a pressed disc.
In a rewritable DVD, the recordable layer is a special metal alloy that changes characteristics when struck by a laser. As the writing surface changes from crystalline to amorphous, this alters its reflectivity, recording data in much the same way the heat sensitive dye on a recordable disc does. However, the process is reversible, and you can erase the disc, returning the surface to its original state. Unfortunately, rewritable DVDs do not allow selective deletion, as magnetic hard drives do; you must erase the entire disc before reuse.
There are two major types of rewritable discs. DVD-RW discs grew out of a format created by Pioneer in 1997. A group of manufacturers called the DVD+RW Alliance maintains a competing standard. Both discs can hold about 4.7 gigabytes of data, but the two formats are completely incompatible and use different types of media. Fortunately, it is easy to find rewritable DVD drives that can write to both types of disc, and computer DVD drives can read from either format easily. If you are burning discs for use in a standalone DVD player or other device, however, you should consult the device's manual to determine which type of DVD you should use.
A third type of recordable DVD, known as DVD-RAM, offers some advantages over DVD+RW and DVD-RW discs. DVD-RAM discs use a file system that includes built-in error correction and allows DVD burners to write data to the disc incrementally, unlike other rewritable discs that you must burn or erase all at once. These discs work well in digital camcorders, allowing you to edit video on the fly or re-record segments without having to clear the disc first. DVD-RAM is not as widely supported as the other two formats, however, so make sure your burner and other devices can use DVD-RAM discs before purchasing blank media.
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