Hypervisors

Type 1 hypervisor

Type 1 hypervisor means that vm is running natively (bare metal) on hardware.

Examples: VMWare vSphere / ESXi, KVM, Xen / Citrix XenServer

Type 2 hypervisor

Type 2 hypervisor means that vm is running on another peice of software. Basically on a host OS.

Example: VMWare workstation.

QEMU, KVM and QEMU with KVM

QEMU is a type 2 hypervisor but it can become Type 1 if used with KVM.

Here’s how:

Virtualization technologies like VT-x (intel) and AMD-V, map physical CPU directly to Virtual CPU.

KVM enables mapping of physical cpu to virtual cpu. This provides hardware acceleration for virtual machine.

QEMU can use KVM (Linux kernel module) as vert-type to take advantage of this hardware acceleration and thus can become type 1.

QEMU used without KVM, can use TCG (Tiny co de generator); if your cpu doesn’t support hardware virtualization. Then it’s a type 2 hypervisaor.

Further Reading