Design Fundamentals
How to run the round — scope it, size it, draw it, and defend the choices.
7 topics
Running a System Design Interview
A timeboxed structure for the 45 minutes, so the round is a conversation you're leading rather than a quiz you're answering.
core25 minRequirements & Scoping
Turning a one-line prompt into a short list of functional requirements and the four non-functional numbers that decide the architecture.
core20 minBack-of-the-Envelope Estimation
Converting user counts into requests per second, bytes per day and storage per year — fast enough to do it out loud without a calculator.
core20 minLatency Numbers Worth Knowing
What each hop in a request actually costs, so you can tell which part of a design is slow before you build it.
core15 minDrawing the High-Level Design
Getting from requirements to a diagram that can actually be evaluated — client to storage, happy path first, every box justified.
core20 minArguing a Tradeoff
How to make a design decision out loud so it survives follow-up — name the alternative, name the cost, name the condition that would change your mind.
core20 minHow Design Rounds Are Failed
The recurring failure modes — designing before scoping, boxes with no numbers, silence, and over-engineering — and what to do instead.
core15 min