1. A method comprising: executing a host operating system according to a host system architecture of a first register size; executing a guest operating system according to a guest system architecture having registers of a second size different from said first size; translating instructions from the guest operating system into instructions that run on the host operating system; mapping processor states of a first virtual processor supporting the guest system architecture with processor states of second virtual processor supporting the host system architecture; and storing the processor states of the first virtual processor that are not mapped with the processor states of the second virtual processor.