Module 1 · Foundations

Foundations & Mental Models

A gentle introduction to the four questions behind every system design: how fast is one request, how many requests arrive, what happens when demand grows, and what must remain correct?

7 lessons available170 minutes

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Lesson plan

What you will learn

01Hardware Numbers Every Systems Engineer Must KnowInternalize CPU register speeds, L1/L2/L3 cache misses, DRAM access times, NVMe vs SATA throughput, and datacenter vs intercontinental network latencies. 20 min 02Network Protocols & Real-Time Communication ParadigmsCompare TCP, UDP, QUIC (HTTP/3), gRPC Protocol Buffers, WebSockets, Server-Sent Events, and Long Polling for high-performance and real-time architectures. 25 min 03Latency vs. Throughput & The Tail at ScaleMaster Little’s Law for concurrency sizing, unmask the danger of arithmetic averages, and mitigate the Dean & Barroso tail latency amplification effect. 25 min 04Scalability Dimensions & Universal LawsUnderstand horizontal vs vertical scale limits, Amdahl’s Law for parallelization, and Neil Gunther’s Universal Scalability Law accounting for crosstalk and contention. 25 min 05Availability, SLOs, SLIs & Error BudgetsQuantify uptime math (99.9% vs 99.99%), calculate serial vs parallel system reliability, and establish actionable SRE error budget burn rates. 20 min 06ACID vs. BASE & The Consistency SpectrumDeconstruct database transaction guarantees from Serializable isolation down to Eventual consistency, exploring snapshot isolation, dirty reads, and write skew. 30 min 07CAP Theorem & PACELC FrameworkFormalize Gilbert & Lynch’s CAP proof, dissect why network partitions cannot be avoided, and adopt Daniel Abadi’s PACELC model for real-world databases. 25 min

Module outcome

Estimate a small system with simple arithmetic, recognize the difference between latency and throughput, and explain availability and consistency in plain language before learning the formal equations.

Prerequisite

Comfort with basic web requests (a browser calling a server) is enough. Any unfamiliar networking term is introduced in the lesson.

Mental model

A system is a set of waiting lines connected by networks and storage. Start by asking how much work arrives, how quickly each step serves it, and which promises the user cannot lose.

Module challenge

Tiny URL Shortener: First System Design Walkthrough

Estimate a small URL-shortener service from a plain-language traffic story, then explain which assumption would change the design first.

Convert one million daily visits into an average and a simple burst estimate.
Name one user promise (for example, “a saved link should not disappear”) and protect it.
Explain the design aloud using assumptions, units, and one trade-off.