Interrupt request level. The hardware priority level at which a given kernel-mode routine runs, masking off interrupts with an equivalent or lower IRQL on the processor. A routine can be preempted by an interrupt with a higher IRQL. Running at raised IRQL on a given processor has no effect on the IRQL of any other processor in a symmetric multiprocessor machine. For more information see the topic, Managing Hardware Priorities. See also IDT, interrupt object, IRQ, ISR, multiprocessor machine, and priority.

an IRQ Level that the Operating System is operating at