Question 1

What is the difference between HLD and LLD?

Accepted Answer

High-Level Design (HLD) covers the overall system architecture — components, services, databases, and how they communicate. Low-Level Design (LLD) covers class structures, design patterns, and code-level implementation of individual components.

Question 2

What framework should I use to answer system design questions?

Accepted Answer

A reliable 4-step framework: (1) Clarify requirements and scale, (2) Estimate capacity and constraints, (3) Design the high-level architecture, (4) Deep-dive into critical components. Always discuss trade-offs at each step.

Question 3

What topics must I know for system design interviews?

Accepted Answer

Load balancing, caching (Redis, Memcached), databases (SQL vs NoSQL, sharding), message queues (Kafka), CDNs, rate limiting, consistent hashing, CAP theorem, and API design. Read "Designing Data-Intensive Applications" by Kleppmann.

Question 4

When do system design rounds start appearing?

Accepted Answer

Typically from SDE-2 level onwards (3+ years experience). Some companies test basic system design at SDE-1 level. The depth and complexity expected increases sharply with seniority.

Question 5

How long should I take to answer a system design question?

Accepted Answer

In a 45–60 minute round: 5 min on requirements, 5 min on capacity estimation, 20 min on high-level design, 15 min on deep-dives, 5 min for Q&A. Practice talking through your thinking aloud — interviewers follow your reasoning.

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