On Amazon EC2, the instance type you choose determines the amount of physical memory (RAM) that you get. Larger instance types with lots of RAM are more expensive. So if you want more RAM on a medium or small EC2 instance, you can define some storage space on your disk to act as RAM when needed. The disk area you use for this purpose is called a swap file. This article explains swap files and demonstrates how to set up a 2GB swap file using ephemeral storage on an m3.medium instance of Amazon EC2 that has only 3.75GB of RAM by default.