04.01 · Cheat sheet
System Design
The building blocks, numbers and trade-offs to bring into a design round.
The 45-minute framework
- Requirements: functional (what it does) and non-functional (scale, latency, availability).
- Estimates: users, requests per second, storage.
- API: the main endpoints.
- Data model: tables or documents, keys.
- High-level design: boxes and arrows.
- Deep dive: bottlenecks, scaling, failures.
- Trade-offs: say what you gave up and why.
Numbers to estimate with
| Thing | Roughly |
|---|---|
| Memory read | 100 ns |
| SSD random read | 0.1 ms |
| Same-datacenter round trip | 0.5 ms |
| Disk seek | 10 ms |
| Cross-continent round trip | 150 ms |
- 1 day ≈ 86,400 s ≈ 10⁵ s. 1 million requests a day ≈ 12 per second.
- 2¹⁰ ≈ 10³. 1 KB × 1 billion = 1 TB.
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Inside: 9 sections.
- The 45-minute framework
- Numbers to estimate with
- Scaling the app
- Caching
- Databases
- CAP and consistency
- +3 more
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Item 11 of 12 · updated 2026-10-13