A processor lockstep is a technique used to achieve high reliability in a microprocessorsystem. This is done by adding a second identical processor to a system that monitors and verifies the operation of the system processor.
* The two processors are initialized to the same state during system start-up, and they receive the same inputs (code, bus operations and asynchronous events), so during normal operation the state of the two processors is identical from clock to clock. They are said to be operating in lockstep. The lockstep technique assumes that an error in either processor will cause a difference between the states of the two processors, which will eventually be manifested as a difference in the outputs, so the lockstep system monitors the outputs of the two processors and flags an error in the case of a discrepancy. [* Adapted from IBM PowerPC Tips]