Virtual IRQ's and what they do

Question

I'm surprised but from what I can find there is very little good information on what these really are. Some say they are actually virtual (software interrupts) some say hardware, and a lot say stuff that I at least know is partly untrue. What are these really and how do they work? What is there purpose? Are there actual hardware lines on the motherboard that represent them?

Answer 1

There is no generally accepted, single definition of "virtual IRQ".

It may refer to a software scheme of representing interrupts which abstract physical IRQ's (allowing for sharing of a physical IRQ line by two devices, for instance).

Or it could be something else. For instance, simulated interrupts in a virtual machine. If your Virtualbox gets an interrupt request from its virtual Ethernet card, that can be nothing other than a virtual interrupt request.

Regarding dedicated copper lines on a motherboard: it's more sensible to send a message.

See for instance:

http://en.wikipedia.org/wiki/Message_Signaled_Interrupts

(Is that "virtual IRQ"?)