Lockstep

Lockstep refers to a mode of operation in which multiple components execute in exact, synchronized steps, producing identical results. The term originated from marching in lockstep but has expanded to technical and organizational contexts. In computing, lockstep aims to enhance determinism, reliability, and fault tolerance.

In hardware and fault-tolerant systems, lockstep often means two or more processors execute the same instructions on identical data, comparing results to detect faults. This is a form of N-modular redundancy or dual modular redundancy with comparison. If a mismatch occurs, a fault can be isolated and corrected. Lockstep designs are used in avionics, space systems, and secure environments where high reliability is required, though they incur extra cost and power use.

In distributed systems and state machine replication, lockstep describes a protocol where replicas process the same sequence of operations in the same order, maintaining identical state. Deterministic execution and agreed input streams are essential; failures are detected by divergence in state, enabling recovery or reconfiguration.

In real-time multiplayer games and simulations, a lockstep networking model advances the simulated clock only when all clients have submitted their inputs for the current tick. This ensures deterministic results across clients but can increase latency and sensitivity to lag, leading to techniques such as input buffering or rollback.

In organizational contexts, "lockstep" denotes a progression scheme where promotions, salaries, or other statuses advance at fixed, uniform steps regardless of individual performance, or where curricula align across groups. Critics argue it can reduce incentives for merit, while supporters cite predictability and fairness.