You may also want to look at how an external dual layer DVD burner works; though
, more often than not you will mostly come across DVD burners that only write and read single layer discs. Other top contenders for the title "best external DVD burner" include products from Plextor, MegaSTOR, HP, Lite ON and IOMega - but, it is safe to say that, in the end, Sony will get your nod.