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APIC

APIC stands for Advanced Programmable Interrupt Controller and is an interrupt controller integrated in the CPU.
APIC replaces the Intel 8259 programmable interupt controller (PIC).
An I/O APIC provides more than 16 interrupt requests (IRQs), thus IRQ sharing is not required anymore which improves reliability.
An APIC is accessed through memory-mapped registers and provides interrupt service to each CPU, used for IPIs and local interrupts.
APIC is programmed through the LVT (local vector timer) register.

IO-APIC

An I/O APIC is an SMP-capable replacement for PC-Style interrupt controllers. Most (all?) SMP systems and many recent uniprocessor systems have one.

Linux CONFIG

CONFIG_X86_UP_APIC, CONFIG_X86_UP_IOAPIC

Misc

Apparently, Windows installs different kernels depending on the availability of APIC.

See also

I find it confusing that ACPI has the same letters like APIC.

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