> I've always seen this as an example of why physical/hardware interlocks are really important when you're mixing software with hardware that can easily hurt pe

> I've always seen this as an example of why physical/hardware interlocks are really important when you're mixing software with hardware that can easily hurt people. Not only that, but running in to the interlock should be considered a notable event. The machine should not just continue operating as normal, it should be clear to the operators that something potentially dangerous has occurred and should be investigated. It seems like they had just assumed that because no one had managed zap someone with the previous models that the software must have been perfect, even though the previous models had hardware interlocks preventing the dangerous scenario. Those interlocks had presumably been tripped many times, just no one ever brought it to the attention of the vendor. If a system trips a safety interlock it should fail to a safe configuration and remain there until reset by someone capable of investigating why it was tripped in the first place. Modern traffic lights are a good example of doing it right. In those cabinets you see at every intersection, right next to the traffic light controller will be a device called a conflict monitor. This device will be wired to the circuits feeding the light heads themselves. If two conflicting movements are indicated for whatever reason, be it a failure of the controller, a short in the wiring, etc, the conflict monitor will trip and set the intersection to a fail-safe mode (usually either all-red blink or yellow blink for a main road with reds elsewhere) until manually reset by a human. --- > I'm also always amazed by how few people seem to know about the Therac-25 incident, especially people that work in therapeutic radiation roles (in the UK anyway). That's interesting, at least amongst my "techie" friends it's common knowledge. Many of us who went to college for computer science related things had it used in one class or another to get across the point that bad software can kill people in really unexpected ways. I guess maybe the medical side of things doesn't find it worth as much attention because they don't have as much to learn from it.