Intel LGA775 User Manual page 49

BIOS SETUP
Reload Global Timer Events
The HDD, FDD, COM, LPT Ports, and PCI PIRQ 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 attention 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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