Message Signaled Interrupts (MSI) are a method of signaling interrupts, using special in-band messages to replace traditional out-of-band signals on dedicated interrupt lines. While message signaled interrupts are more complex to implement in a device, they have some significant advantages over pin-based out-of-band interrupt signalling, such as improved interrupt handling performance. This is in contrast to traditional interrupt mechanisms, such as the legacy interrupt request (IRQ) system.
Message signaled interrupts are supported in PCI bus since its version 2.2, and in later available PCI Express bus. Some non-PCI architectures also use message signaled interrupts.