What is the difference between a standard DVD and a Dual Layer DVD? 

A dual layer DVD looks and feels just like a standard DVD. However, dual layer DVD’s allow the user to record two separate layers of data onto the same disc, meaning that it can store almost twice as much data as a typical DVD.
A standard recordable DVD has a storage capacity of around 4.7GB, while a Duel Layer DVD will allow for around 8.5GB.