1. In a computer including an I/O device, a method comprising using a virtual machine monitor to commence virtualization of the I/O device at runtime, wherein runtime is a period of execution in the computer after boot and before shutdown of the computer, wherein virtualization of the I/O device is performed by: redirecting interrupts for the I/O device to interrupt handlers in the virtual machine monitor; enabling the virtual machine monitor to intercept I/O accesses by an operating system; commencing emulation of the I/O device using a state machine; wherein the virtual machine monitor determines whether the I/O device is performing an I/O sequence, and delays commencing the virtualization until the virtual machine monitor determines that the I/O sequence has completed.