Not all DVDs are the same inside. Beneath their silvery rainbow surfaces, different kinds of DVDs are able to store different amounts of data. DVDs can be single-sided or double-sided and on each side there can be more than one layer for storing data. Like CDs, some DVDs can be written on only once, while others can be erased and used again and again. Depending on how it was manufacturered, a DVD can hold anywhere from a maximum of 4.7 GB to 17 GB.
Standard, single-layer DVDs can store approximately 4.7 GB of data. These single-layer discs are the most common blank discs sold. Some DVDs are manufactured as dual-sided, single-layer discs, which means that data can be stored on both sides of the disc. These discs hold 9.4 GB of data. Blank DVDs that can be written on once are identified as "DVDR" or "DVD +R," while those that can be deleted and rewritten are identified as "DVD +RW."
Dual-layer discs have two layers of readable data on one side and can typically hold up to 8.54 GB of data. When you buy a movie on DVD, it is usually in this format, since this amount of space allows for better picture quality and more special features. Blank, writable discs of this type are usually marked "DVDR DL" or "DVD +R DL." Although rare, double-sided, dual-layer discs can hold up to 17 GB of data. In June 2014, there were no manufacturers offering blank dual-layer rewritable discs, or "DVD RW DL."
While standard DVDs are 12 cm in width, you may sometimes find smaller 8 cm DVDs used for software or promotional videos. A single-sided, single-layer 8 cm DVD can hold 1.46 GB, while a single-sided dual-layer 8 cm DVD can hold 2.66 GB. Dual-sided, single-layer versions can store up to 2.92 GB, while a dual-layer, dual-sided 8 cm DVD can hold up to 5.32 GB.