movie disc player program that services interrupts related to audio output and cd reading the guest operating system stack may run in domu and might typically comprise the guest operating system including isrs together with windows u00ae compatible applications programs for example the microsoft u00ae outlook email program issues arise as to the use by the two operating system stacks of a single shared peripheral device for example a cd compact disk drive or an output sound system since they run in separate vms the two operating systems are typically unaware u2014 each of the other and indeed may contain no support for running under a hypervisor at all thus relying on hypervisor invisibility from the operating systems 39 s standpoint by design some peripheral devices may be handled by virtualization of all i o input output associated therewith and others may be handled at times by a pass thru technique wherein mmio memory mapped input output and pio programmed input output execute without causing traps such traps may commonly be designed to provide hooks for simulation emulation or similar capabilities pio is used by i o instructions as contrasted with memory access instructions on cpus that have separate memory spaces intended primarily for providing i o device addressing and memory addressing allowing at various times access to peripheral devices from either or both operating system stacks raises implementation issues beyond the scope of the present invention successful isr management without vm to vm resource conflicts and other conflicts is also a challenge and discussed further below generally speaking operating systems are designed.