ATO Mission Computers Practice Test

Triple-modular redundancy uses three identical processing paths running in parallel and a majority vote to determine the final output. The idea is that if one path develops a fault and starts producing a wrong result, the other two paths will still agree on the correct result, so the voter selects the correct output and the fault is masked. This setup greatly boosts reliability because you only need two of the three paths to be correct for the system to behave correctly, reducing the impact of a single component failure. To give a sense of the improvement, if each path has reliability R, the chance that the majority output is correct is R^3 + 3R^2(1−R). That yields a substantial increase over a single path, especially when R is already high (for example, with R about 0.99, the overall reliability becomes around 0.9997). However, remember this protection is against a single faulty path; two simultaneous faults can still defeat the majority decision, and the voter itself is an extra component that can fail.