What is system design?

System design is the process of defining the architecture, components, modules, interfaces, and data flow of a system to satisfy specified requirements. It bridges the gap between high-level requirements and low-level implementation details. In software engineering, system design involves making decisions about: Architecture — monolith vs microservices, client-server vs peer-to-peer; Data storage — which databases, how to structure data, replication strategy; Scalability — how the system handles growth in users, data, and traffic; Reliability — how the system behaves when components fail; Performance — latency, throughput, response times; Security — authentication, authorization, encryption. System design interviews evaluate a candidate's ability to think at scale and make informed engineering trade-offs. The process typically involves: clarifying requirements, estimating scale (capacity planning), designing high-level architecture, deep-diving into components, identifying bottlenecks, and discussing trade-offs. There is no single "correct" answer — good system design is about demonstrating sound reasoning and awareness of constraints.