3.5.5.4IRQ Wakeup Events
The VGA, LPT & COM, HDD & FDD, and PCI master are I/O events which can prevent the system from entering a power saving mode or can awaken the system from such a mode. When an I/O device wants to gain the attenetion of the operating system, it signals this by causing an IRQ to occur. When the operating system is ready to respond to the request, it interrupts itself and performs the service.
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