Editing Intel 8259 (section)

== PC/XT and PC/AT ==
{{main|Interrupt request (PC architecture)}}
The PC/XT [[Industry Standard Architecture|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.