1. A computer system comprising: a physical computer; a virtual machine monitor executable on the physical computer and configured to create an emulation of at least one guest operating system adapted to control the physical computer; and a host executable on the physical computer that manages physical resources coupled to the physical computer on behalf of the virtual machine monitor and the at least one guest operating system, the host adapted to virtualize a Peripheral Component Interconnect (PCI) configuration address space whereby the at least one guest operating system controls PCI input/output (I/O) devices directly and in absence of I/O emulation for memory-mapped I/O registers and I/O port registers, and emulates accesses to configuration space.