Single-side/Single-layer

• Single-side/single-layer discs, also called DVD-5 discs, can store 4.7 GB of information. Most recordable and all rewritable DVDs are in this format.
  
  

Single-side/Dual-layer

• Some DVDs employ dual-layer technology which increases storage to 8.5 GB, which is nearly double the storage capacity of single-layer discs. Most movies sold on DVD are on dual-layer, single-sided discs, which also are called DVD-9 discs, because the added storage space allows for added features like extra audio tracks and deleted scenes.
  
  

Double-sided Discs

• There are double-sided discs that have data stored on both sides of the disc. A double-sided single-layer disc (DVD-10) can hold 8.74 GB of data, while a double-sided dual-layer discs (DVD-18) can hold 15.90 GB, the most of any DVD format. Double-sided discs are sometimes used for movies, but many consider them inconvenient and prone to scratching, so single-layer media is usually preferred.