A computer system includes a Hypervisor having the highest privilege level; a Primary Virtual Machine Monitor (VMM) running with the same or fewer privileges than the Hypervisor; and a Primary Virtual Machine (PVM) without system level privileges and having a Primary operating system (POS) running within it. The POS can be the same operating system that ran on the computer system prior to activation of the Hypervisor. The POS can have hardware drivers used by other components for accessing hardware through the POS. The Hypervisor can have hardware drivers used by other components for accessing hardware through the Hypervisor. Alternatively, the POS can have some hardware drivers used by other components for accessing hardware, and the Hypervisor can have other hardware drivers used by the other components for accessing other hardware through the Hypervisor. The POS can have direct access to at least some real hardware devices.