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On thex86 architecture, adouble fault exception occurs if theprocessor encounters a problem while trying to service a pendinginterrupt orexception. An example situation when a double fault would occur is when an interrupt is triggered but the segment in which theinterrupt handler resides is invalid. If the processor encounters a problem when calling the double fault handler, atriple fault is generated and the processor shuts down.
As double faults can only happen due tokernel bugs, they are rarely caused byuser space programs in a modernprotected modeoperating system, unless the program somehow gains kernel access (someviruses and also some low-levelDOS programs). Other processors likePowerPC orSPARC generally save state to predefined and reserved machine registers. A double fault will then be a situation where another exception happens while the processor is still using the contents of these registers to process the exception. SPARC processors have four levels of such registers, i.e. they have a4-window register system.