CAP and Consistency Models

The CAP theorem says that during a network partition a distributed system has to choose between consistency and availability; you cannot have both while the network is split. PACELC extends it: even when there is no partition, you trade latency against consistency. Consistency models form a spectrum from linearizability (acts like one copy, real-time order) down through causal to eventual consistency. Logical clocks (Lamport, vector) order events without synchronized wall clocks. AI, ML, and GenAI engineer interviews probe it because every replicated store, queue, and feature pipeline sits somewhere on this spectrum, and naming the point precisely sets senior candidates apart.