In computing, a programmable interrupt controller (PIC) is an integrated circuit that helps a microprocessor (or CPU) handle interrupt requests (IRQs) coming from multiple different sources (like external I/O devices) which may occur simultaneously.
[citation needed] PICs often allow mapping input to outputs in a configurable way.
The IRR specifies which interrupts are pending acknowledgement, and is typically a symbolic register which can not be directly accessed.
There are a number of common ways of acknowledging an interrupt has completed when an EOI is issued.
In modern times, this is not included as a separate chip in an x86 PC, but rather as part of the motherboard's southbridge chipset.