A computer includes hardware, a virtual machine monitor, and first and second operating system instances. The virtual machine monitor is used to expose a first operating system instance to a first hardware partition and prevent the first operating system instance from discovering a second hardware partition; and expose a second operating system instance to the second hardware partition and prevent the second operating system instance from discovering the first hardware partition. The virtual machine monitor is also used to share at least some of the hardware among the first and second operating system instances.