Editing Double fault (section)

{{Short description|A type of processor fault}}
{{about|the computing term|the tennis term|Double fault (tennis)}}
{{refimprove|date=December 2009}}
On the [[x86]] architecture, a '''double fault''' exception occurs if the [[central processing unit|processor]] encounters a problem while trying to service a pending [[interrupt]] or [[Exception handling|exception]]. An example situation when a double fault would occur is when an interrupt is triggered but the segment in which the [[interrupt handler]] resides is invalid. If the processor encounters a problem when calling the double fault handler, a [[triple fault]] is generated and the processor shuts down.

As double faults can only happen due to [[kernel (operating system)|kernel]] bugs, they are rarely caused by [[user space]] programs in a modern [[protected mode]] [[operating system]], unless the program somehow gains kernel access (some [[virus (computing)|virus]]es and also some low-level [[DOS]] programs). Other processors like [[PowerPC]] or [[SPARC]] 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 a [[Register window|4-window register system]].