A Dual/Double Layer DVD holds 8.5 GB of data. Depending on who you ask, 8.5GB is either 8500 MB (8.5 * 1000) or 8704 MB (5.5 * 1024). The official size of a gigabyte is 1000 MB and a gibibyte is 1024 MB. This was not always the case, causing the confusion over 1000 vs 1024 megabytes to a gigabyte. You should be aware that both could be true depending on the vendor and technology being used.