This paper considers the realizing examples for automatic device with fault tolerance. The most important device structures with and no reservation are compared. The most common ways to increase fault tolerance are considered. The building for device structures with duplication and optimal. The construction structures with redundancy and build in testing equipment BITE. We consider fault tolerance in systems of high risk of sudden failure. A comparison of economic composes in the recovery efficiency of devices. Proposed to build devices with high-availability operating conditions with the inevitable risk of harmful effects. We consider the probabilistic assessment of fault tolerance on each occasion.