What is I/O APIC?

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APIC architecture is used in solving interrupt routing efficiency issues in computer systems which have multiprocessors. This whole system is one of advanced programmable interrupt controllers. I/O APICs include a redirection table; this table helps in routing the interrupts from peripheral buses to local APICS.

APIC is the abbreviated form of Advance Programmable Interrupt Controller. The BIOS (Basic Input Output System) feature is used to enable and disable a motherboard’s APIC. This APIC not only provides multiprocessor support but it also helps in faster interrupt handling. This feature is supported in newer and modern operating systems like Windows XP, Windows 2000, etc.  It is not included in operating systems like Windows 95, Windows 98, DOS, etc. People using the newer operation systems should enable the I/O APIC feature and disable it if they are using old operating systems.

The I/OA PIC function is very important for multiprocessor support; this feature improves the user’s experience. APIC is an interrupt controller and all parts of the system is connected to an APIC bus. While local APICs delivers interrupts of a single processor, I/O APICs help in collecting interrupt signals from I/O devices. I/O APICS then sends messages to the local APIC, whose devices are to be interrupted. All I/O APICs are provided with a random number of IRQs or interrupt inputs. Current I/O APICs usually have 24 inputs, however it may vary, and the number of inputs may go up to 64.

It must be noted that a system can have as many as 8 I/O APICS. Each I/O APIC in such systems has a number of inputs which can amount to a hundred IQRs. These IQRs are available for device interrupts. I/O APICs are imperative to the system, because the local APICS will be of absolutely no use without them.

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