APIC is a chip that remaps IOs and IRQs of your computer to the CPU(s). This is needed on mulitple processor systems. Windows also uses APIC to configure IRQ's for the rest of the hardware. It eliminates IRQ conflicts and it makes many more IRQ's available.
This is not to be confused with ACPI (Advanced Configuration and Power Interface) which is a specification for the efficient handling of power consumption in desktop and mobile computers.
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