There has been an ongoing battle between two industry groups trying to establish a standard DVD recordable and rewritable format. The two groups, DVD+RW Alliance and DVD Forum, have established their own two-layer DVD disc formats, which they identify using slightly different names. The DVD+RW Alliance calls its format "double layer" and the DVD Forum calls its format "dual layer." Sony is part of both organizations and has often been among the first manufacturers to offer products combining the different formats.The internal DRU-800A drive ships for $130 and the external DRX-800UL will ship for $210 at the end of the month. Source: CNET
Sony debuts double and dual-layer DVD writers

Sony launches two new double and dual-layer DVD writers today, enabling a storage capacity of 8.5GB. Both drives support read and write to DVD+/-R, DVD+/-RW, CD-R and CD-RW discs, as well as DVD+/-R dual and double-layer discs.