Embodiments of the present invention provide secure virtual-machine monitors and secure, base-level operating systems that, in turn, provide secure execution environments for guest operating systems and certain special functions that can interface directly to base-level operating systems. Security is accomplished by employing a small, verifiable component of a secure foundation that executes at highest privilege between the hardware interface and the virtual-machine monitor. The virtual-machine monitor and secure foundation employ virtual-machine-monitor-resident guest-operating-system monitors, memory compartmentalization, and authenticated calls to securely isolate computational entities from one another within the computer system.