This architecture has some advantages; first and most important is the ability of the VMM to support the diversity of I/O devices in the x85 market. Another advantage is for the VMM to use scheduling, resource management and other services that the Host operating system environment offers. The major disadvantage of this method is the increase of performance overhead for I/O device virtualization. Every I/O command needs to transfer to the Host operating system, and then using the Host OS’s software layers to communicate with I/O devices [3].