There are two different virtualization types supported on EC2 that can deliver differing features and, in the past, differing performance to the visualized operating system and they are defined as the following:

• Fully visualized or Hardware Virtual Machine (HVM)
• VMs with some direct access to hardware or paravirtual (PV) machine 

HVM are presented with a set of virtual resources (virtual CPU, disk, network, and GPU) and allow for a lot of flexibility when it comes to virtual computing as the instance is essentially fully decoupled from the hardware. That means it can operate on multiple different hardware profiles with no modification at all as the hardware is always presented as virtual devices.

In the past, PV was used to allow for better performance versus HVM due to its nature of allowing the guest operating system to access some underlying hardware and perform direct execution on the CPU, but the advances made in the way HVM operates and the virtualization extensions built into modern CPUs mean that the advantage is now irrelevant. Also, advanced services such as GPUs and enhanced network devices are not supported on PV instances. As there is no advantage to PV anymore, the newest EC2 instance types now only support the HVM virtualization instance type.