W/ regard to space-based and airborne systems (commercial jets also actually operate in a fairly high radiation environment): The risk of faults is not only no

W/ regard to space-based and airborne systems (commercial jets also actually operate in a fairly high radiation environment): The risk of faults is not only non-zero, it's expected. Google 'single event upset' and 'nor flash soft error. Short version - (SEU) any bit in your RAM, CPU, peripherals, or databus can (and will, eventually) be randomly flipped in a high radiation environment. (Soft Error) - A random cell in your flash may be pushed into an indeterminate voltage range, and will return a different value every time you read it. So, for instance, you may CRC it, think it's good, copy it to RAM, and then the CRC of the RAM copy will fail because you got a different value the second time you read it. There are ways to deal with this. Google 'lockstep CPU' for information on a common, fairly hardcore approach. Basically you replicate the CPU (and the rest of the hardware) and cross-check every single clock cycle; you essentially have two or more computers in one box doing the work of a single computer. As you can imagine, this hardware is typically entirely custom, tested more thoroughly than anything you've ever imagined (unless you're in a safety critical industry yourself), and very expensive to design & test. Hardware refresh cycles are typically measured in decades, often governed by component obsolescence.