CAP and Consistency Models

The CAP theorem says that during a network partition a distributed system must 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. Applied-AI interviews probe it because every replicated store, queue, and feature pipeline lives somewhere on this spectrum, and naming the point precisely separates senior candidates.