A master-checker is a hardware-supported fault tolerance method for multiprocessor systems.

Two processors calculate in parallel the same functions to increase the probability that the result is exact.

In technical terms

The checker-CPU is synchronised at clock level with the master-CPU and processes the very 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.