Embodiments of the present invention are directed to methods for virtualizing interrupt modes on behalf of interrupt-generating devices, including I/O-device controllers, so that newer interrupt-generating devices that lack older interrupt modes can be used in systems that continue to rely on older interrupt modes. In one embodiment of the present invention, a PCIe switch or PCIe-based host bridge is modified, or a new component introduced, to provide an interrupt-mode virtualizing function, or virtual interrupt-mode interface, that provides a virtual interrupt mode on behalf of interrupt-generating devices, such as I/O-device controllers, to operating systems, BIOS layers, and other components that communicate with the I/O-device controllers.