Linux Amazon Machine Images use one of two types of virtualization: paravirtual (PV) or hardware virtual machine (HVM). The main difference between PV and HVM AMIs is the way in which they boot and whether they can take advantage of special hardware extensions (CPU, network, and storage) for better performance.
For the best performance, we recommend that you use current generation instance types and HVM AMIs when you launch your instances. For more information about current generation instance types, see the Amazon EC2 Instances detail page. If you are using previous generation instance types and would like to upgrade, see Upgrade Paths.
For information about the types of the Amazon Linux AMI recommended for each instance type, see the Amazon Linux AMI Instance Types detail page.