How should I start a system design answer?

Definition:

System design is the process of choosing components, data flows and trade-offs that meet a product's requirements. It starts with what users need and the scale and failure conditions the system must handle. A design is easier to evaluate when assumptions are explicit instead of hidden behind a list of technologies.

Key points:

• Ask about users, main actions, traffic, data size and response-time needs.

• Clarify which data must be immediately correct and what can be delayed.

• Draw the simplest working flow, then discuss bottlenecks and failures.

• Estimate the busiest operations and data growth using the given numbers, then identify where correctness is more important than low latency.

Interview point:

• State assumptions aloud and revise the design when a requirement changes; the reasoning matters more than a familiar diagram.