Master-checker or master/checker is a hardware-supported fault tolerance architecture for multiprocessor systems, in which two processors, referred to as the master and checker, calculate the same functions in parallel in order to increase the probability that the result is exact. The checker CPU is synchronised at clock level with the master CPU and processes the same programs as the master. Whenever the master CPU generates an output, the checker CPU compares this output to its own calculation and in the event of a difference raises a warning.
The master-checker system generally gives more accurate answers by ensuring that the answer is correct before passing it on to the application requesting the algorithm being completed. It also allows for error handling if the results are inconsistent.