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
In a multiprocessor system, an IO APIC module. See Figure 61-5 on page 1506.
Figure 61-5. The Pentium® 4 Eliminated the ...