Foundations

How a request crosses the network, the trade-offs every design makes, and how to estimate and structure an interview answer. 3 modules, about 3 hours of reading. Every lesson ends in something to do.

How Systems Work

Introduction to System DesignWhat system design really is, why it exists, and how to start thinking like an architect from day one.Beginner22 min
How the Web WorksWhat actually happens between typing a URL and seeing a page — DNS, TCP, TLS, HTTP — and why every later topic is an optimisation of this path.Beginner17 min
Networking BasicsAddresses, ports and the layers underneath every request — the vocabulary the rest of this course assumes you already have.Beginner17 min
Data Encoding and EvolutionHow data becomes bytes, and how to change its shape later without breaking everyone who already reads it.Beginner17 min
Storage and the Memory HierarchyWhy data lives in four different places at once, and how the gap between them decides most of your architecture.Beginner17 min

Core Trade-offs

Scalability ConceptsVertical vs horizontal scaling, why statelessness decides which you can use, and how to know when to switch.Beginner19 min
Latency vs. ThroughputThe two numbers that describe every system's performance, why averages lie, and what P99 really means.Beginner17 min
Availability vs. ReliabilityWhat the nines actually cost, why redundancy is the only real answer, and how SLA, SLO and SLI differ.Beginner18 min
CAP TheoremThe trade-off you cannot escape once data lives on more than one machine, explained without the jargon.Intermediate16 min

The Interview Toolkit

Back-of-the-envelope EstimationsThe numbers to memorise, the four-step method, and how to turn a rough calculation into a design decision.Intermediate17 min
System Design Interview TemplateA minute-by-minute framework for any design question, with the numbers and phrases that actually earn marks.Intermediate18 min

How Systems Work

Core Trade-offs

The Interview Toolkit

How Systems Work

Core Trade-offs

The Interview Toolkit

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