A Dual Layer DVD is, quite literally, a DVD which is comprised of two data layers - therefore to read all the content from a DL (Dual Layer) DVD, otherwise known as a DVD-9 (single side, double layer), you need a drive which can alter the density at which the laser operates. This is so that the laser can read the topmost layer, with a weaker beam, and then focus the laserlight down to a much finer beam to effectively see 'through' the top, outermost layer and retrieve the content from the inner layer. When DVDs (as in films) are authored to dual layer (as pretty much all DVDs are these days), the mastering house has to be very careful where the layer change takes place, as most DVD players will pause for a fraction of a second while the laser repositions from the outer edge to the inside of the disc (as DVDs, like CDs, are read in a spiral from the centre to the edge) and refocuses to read the second layer. Some more hurriedly-produced DVDs can therefore seem to pause, skip or break up momentarily during the layer transition, which really spoils the experience of watching a film. This slight difference in reading the layers also applies when burning data to a dual layer DVD-R/DVD+R, so your burner needs to be able to refocus the laser to penetrate deeper, past the first layer and reach the second layer. Aside from this small difference between DL DVDs (DVD-9 DVDs) and standard, 4.7Gb DVDs (single layer, single side DVDs, aka DVD-5s), there's nothing amazing about Dual Layer DVDs. Being able to store 8.5Gb of content is a nice bonus though, albeit at the sacrifice of burn speed (whereas my Pioneer burner can easily write to DVD-Rs at 16x, the fastest you or I can burn Dual Layer discs at the moment is 2.4x, a limitation caused due to the greater accuracy required when writing to the deeper layer, if I remember correctly). It's a compromise I'm willing to make though for the advantages of increased capacity. Some further reading which you may enjoy... Webopedia's 'DVD Formats Explained' article: http://www.webopedia.com/DidYouKnow/Hardware_Software/2003/DVDFormatsExplained.asp PCMag's 'Double-stuff DVDs': http://www.pcmag.com/article2/0,1895,1631717,00.asp Hope this is a satisfactory answer for you :)