Which of the following statements about virtualization and VMs is incorrect?

If one physical machine is virtualized into multiple VMs, the physical machine is a host machine, and the VMs are guest machines. The OS installed on the physical machine is the host OS, and that installed on the VMs is the guest OS.

Through virtualization by the virtualization layer, upper-layer software regards the VM as a real machine. The virtualization layer is called VMM (virtual machine monitor) or hypervisor.

OS virtualization does not have an independent hypervisor layer, and servers and clients can have different OSs.

Bare-metal virtualization is a VM monitoring program running on physical hardware.