Amazon is unique in that it uses a shelving process called *chaotic storage*, also known as random storage. The employees store items on the nearest empty shelf, which are each assigned a unique bar code. Every product is also given a bar code so when an order comes in the product can be linked with a shelf via a simple lookup. This has a few advantages over fixed position storage in that empty space can be filled immediately and efficiently, and can accommodate quick changes to product lines. If you need to order anything, you can almost always find it on Amazon.