PCI Express
PCI Express does not have physical interrupt lines, but emulates the 4 physical lines of PCI via dedicated PCI Express Messages such as "Assert_INTA" and "Deassert_INTC". Being message-based (at the PCI Express layer), this mechanism provides some, but not all, of the advantages of the PCI layer MSI mechanism: the 4 virtual lines per device are no longer shared on the bus (although PCI Express controllers may still combine legacy interrupts internally), and interrupt changes no longer inherently suffer from race conditions.