Before the Advent of the APIC

Most IA32-based systems incorporate an Interrupt Controller that receives interrupt requests from IO devices and passes them to the processor (or, in a multiprocessor system, to one or more of the processors). The Interrupt Controller typically consists of one of the following:

  • In a single processor PC-AT compatible machine, a pair of cascaded 8259A PICs (Programmable Interrupt Controllers). See Figure 61-1 on page 1500.

    Figure 61-1. Legacy PC-AT Compatible Interrupt Controllers
    [View full size image]

  • In a multiprocessor system, an IO APIC module. See Figure 61-5 on page 1506.

    Figure 61-5. The Pentium® 4 Eliminated the ...

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