Note that the IRQL value is saved in two locations. The first, which represents the current
IRQL, is the processor control region (PCR), while its extension, the processor
control block (PRCB), contains the saved IRQL in the DebuggerSaveIrql field. The PCR
and PRCB contain information about the state of each processor in the system, such
as the current IRQL, a pointer to the hardware IDT, the currently running thread, and
the next thread selected to run. The kernel and the HAL use this information to perform
architecture-specific and machine-specific actions.