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Dual layer DVDs have the ability to hold twice as much data as a single layer DVD. A single layer DVD only has one layer of the physical disk that can hold any kind of information.
A dual layer DVD adds an additional layer of equal size (hence the name), which, in turn, increases the amount of data it can store. Due to the second layer, however, older DVD burners and DVD players may have a hard time working with a dual layer DVD due to the way the drive's laser was made to function earlier in its design. - There are four types of dual layer DVDs. Disks with a "DVD+R" symbol and a "DVD-R" symbol can only be burned once and then never be rewritten. Older drives could only read and write to either "+" or "-" disks which led to some confusion, but all modern drives can use both types. Disks labeled with "DVD+RW" and "DVD-RW" are designed to be written to and then rewritten again should the need arise. Like a USB drive, these disks can only be erased a finite number of times--an estimated 1,000--before data loss begins to occur.
- A standard, single sided dual layer DVD (where one side of the disk holds data and the other is intended to be labeled) can hold 8.5GB of information. A single layer DVD can hold 4GB. There are also disks that you can buy that hold data on both sides (no side is intended to be labeled), which doubles again the amount of total data the disk can hold--from 8.5GB to 17.1GB.
