I built control computers for nuclear reactors. Those machines are not connected to a network and are guarded by multiple stages of men with automatic machine guns. It was designed to flawlessly run 3x boards each with triple-modular-redundant processors in FPGA fabric all nine processors instruction-synced with ECC down to the Registers (including cycling the three areas of programmable fabric on the FPGAs). They cycle and test each board every month.

What’s your source?