A true hardware watchdog is separate electronics. For example, it's really easy to make an electronic circuit that operates a relay once every 5 minutes, say, u

A true hardware watchdog is separate electronics. For example, it's really easy to make an electronic circuit that operates a relay once every 5 minutes, say, unless a 'restart timer' button is pressed. Connect the relay contacts across the PC reset button, and run a program on the PC that 'presses' (electronically) the 'restart timer' button once a minute, say. Then if the PC fails to boot, it gets reset once every 5 minutes until it does (fairly obviously, another set of relay contacts can be used to trigger an alerting device, e.g. wailing sirens). We use this sort of approach with diskless systems in particular. If there's a power cut, the first boot attempt after power restoration might not work (because the network isn't back up yet). So the diskless systems just sit there, continually attempting a network boot until successfu (at which point the software on the PC hits the 'restart timer' button periodicaly. This is closely related to the concept of a "deadman's handle", for example train drivers who must keep a lever pressed down during operation - if it's released, the train stops automatically.