Must Know

A handful of ideas that hold the rest of this atlas up.

The ideas

• A real system is the bar, not a toy. Every branch produces something that builds, runs, and does what production code does — at smaller scale, not lower rigor.
• Concurrency is a property of the project, not a chapter. It gets harder exactly where the server and the database engine make it hard, not in the abstract.
• Durability means you tested the crash, not that you wrote fsync(). A database engine that has never been killed mid-write hasn't proven anything.
• Parsing shows up everywhere. The shell, HTTP, Git's object format, and SQL are all "turn text into a structure" — the regex-engine branch teaches the technique once, on purpose.
• The spine project is versioned, not monolithic. v0 → v3, same discipline as Atlas I's OS milestones — a working v0 beats an imagined v3.
• Atlas I is a prerequisite, not a reference you skim mid-project. If a syscall or a memory concept feels unfamiliar here, that's a sign to go back, not push through.

Where they live

• Real-system bar and concurrency-as-a-property: Concurrency in Practice, threaded through HTTP Server from Scratch and the database engine.
• Durability and crash testing: KV Store & Durability and Craftsmanship Low-Level II.
• Parsing as a reusable skill: Regex Engine from Scratch, HTTP Server from Scratch, Relational Layer & Query Engine.
• The versioned spine project: KV Store & Durability → Relational Layer & Query Engine.

See also: Start Here · Full Index