spurious IRQ15's, but is rare. PC/XT and PC/AT The PC/XT ISA system had one 8259 controller, while PC/AT and later systems had two 8259 controllers, master and slave. IRQ0 through IRQ7 are the master 8259's interrupt lines, while IRQ8 through IRQ15 are the slave 8259's interrupt lines. The labels on the pins on an 8259 are IR0 through IR7. IRQ0 through IRQ15 are the names of the ISA bus's lines to which the 8259s are attached. Variants See also Advanced Programmable Interrupt Controller (APIC) IF (x86 flag) Interrupt handler Interrupt latency Non-maskable interrupt (NMI) Programmable Interrupt Controller (PIC) References Gilluwe, Frank van. The Undocumented PC. A-W Developers Press, 1997. McGivern, Joseph. Interrupt-Driven PC System Design. Annabooks, 1998. IBM Personal System/2 Hardware Interface Technical Reference - Architectures. IBM, 1990. IBM Publication 84F8933 External links 8259A Programmable Interrupt Controller Intel chipsets IBM PC compatibles Input/output integrated circuits Interrupts