In computer systems with memory protection hardware, illegal addresses, garbled data or garbled code usually caused segment fault, parity error traps and illegal opcode traps, i.e. hardware interrupts that are vectored into kernel mode space. The interrupt handler may then decide what to do, try to recover or print CRASH and dump the registers on the console and then halt or reboot the system.
On mainframes with a separate console processor, the console processor may try to check the sanity of the main processor, but even then, the decision to reboot is usually done manual.
Well, back in those days, the watchdog timers would usually come in the shape of trained personnel. They'ld be taught to check certain status indicators on a regular basis, and raise a fuss if anything appeared to be out of hand..
The classical example of a pre-computer age watchdog would be the "dead-man switch" on locomotives. Unless disarmed regularly by the chauffeur, it would bring the train to a stop.
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Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.
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