Editing Interrupt (section)

===Message-signaled===<!-- This section is linked from [[Interrupt]] -->
{{Main|Message Signaled Interrupts}}

A ''message-signaled interrupt'' does not use a physical interrupt line.  Instead, a device signals its request for service by sending a short message over some communications medium, typically a [[computer bus]]. The message might be of a type reserved for interrupts, or it might be of some pre-existing type such as a memory write.

Message-signalled interrupts behave very much like edge-triggered interrupts, in that the interrupt is a momentary signal rather than a continuous condition.  Interrupt-handling software treats the two in much the same manner. Typically, multiple pending message-signaled interrupts with the same message (the same virtual interrupt line) are allowed to merge, just as closely spaced edge-triggered interrupts can merge.

Message-signalled [[interrupt vector]]s can be shared, to the extent that the underlying communication medium can be shared. No additional effort is required.

Because the identity of the interrupt is indicated by a pattern of data bits, not requiring a separate physical conductor, many more distinct interrupts can be efficiently handled.  This reduces the need for sharing. Interrupt messages can also be passed over a serial bus, not requiring any additional lines.

[[PCI Express]], a serial computer bus, uses [[Message Signaled Interrupts|message-signaled interrupts]] exclusively.