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'''Lockstep''' systems are [[Redundancy (engineering)|redundant]] [[Computer system|computing systems]] that run the same set of operations at the same time in [[Parallel computing|parallel]]. The output from lockstep operations can be compared to determine if there has been a fault.
Sometimes a timeshift (delay) is set between the 2 systems, which increases the detection probability of errors induced by external influences (e.g. [[Voltage spike]]s, [[Ionizing radiation]], or [[In situ]] [[Reverse engineering]]).
To run in lockstep, each system is set up to progress from one well-defined state to the next well-defined state. When a new set of inputs reaches the system, it processes them, generates new outputs and updates its state. This set of changes (new inputs, new outputs, new state) is considered to define that step, and must be treated as an atomic transaction; in other words, either all of it happens, or none of it happens, but not something in between.
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