Message Signalled Interrupts (MSI) are an alternative in-band method of signalling an interrupt, using special in-band messages to replace traditional out-of-band assertion of dedicated interrupt lines. While more complex to implement in a device, message signalled interrupts have some significant advantages over pin-based out-of-band interrupt signalling. Message signalled 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 signalled interrupts.