This paper describes a new interrupt mechanism named message interrupt in the third generation IO bus called PCI Express.The message interrupt mechanism includes Message Signaled Interrupt (MSI) and Virtual INTx Signaled Interrupt which adopt In-Band way instead of Side-Band way.In addition

because of its high efficiency and extensibility

the message interrupt mechanism is of important significance in practice and enhances PCI Express bus to make it become the mainstream in the IO bus.