When an intel processor recieves an interrupt, it looks for an interrupt table. When in protected mode, this table is an array defined by its base and length. If an interrupt which index is outside the length of the array occurs, a special double fault interrupt occurs. If this interrupt is still outside length (The length may be 0), the machine reboots. This is a fairly quick and fairly clean way of doing a warm-boot.

A triple fault is what happens if you get an exception in the double exception handler on an x86 system. When this happens, the CPU enters SHUTDOWN mode; which the PC/AT circuitry converts to a reset. From my interrupt list: "This triple fault is a faster way of returning to real mode on many 80286 machines than the standard keyboard controller reset".

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