OS Primer

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How to Use This Primer ​

This primer is meant to be studied over a few weeks, not skimmed the night before. Each chapter builds a mental model from first principles, then connects it to real systems and to the questions interviewers actually ask.

What's in each chapter ​

  • Core explanation. The concepts in order, each building on the last. Read this part carefully.
  • Diagrams and interactive widgets. Where watching something move makes it click, there is a widget to play with.
  • C examples. Short programs you can compile and run on any Linux machine (gcc -O2 file.c && ./a.out).
  • Why it matters in real systems. How the concept shows up in databases, web servers, language runtimes and ML infrastructure. Senior interviews live here.
  • Interview questions. From basic to senior-level follow-ups, each with a model answer. Try to answer out loud before opening it.
  • Misconceptions. Things that sound right but aren't, and are common in interviews.
  • Going deeper boxes. Collapsed by default. The main text makes sense without them; open them for hardware names and precise details that interviewers sometimes probe.
  • Tap-to-see terms. Words with a dotted underline show a short definition when you tap them. All of them are also on the Glossary page.
  • Flashcards. For review a few days later. They ask why and how, not trivia.

A suggested routine ​

  1. Read a chapter in one sitting, running the code and playing with the widgets.
  2. The next day, go through the flashcards without re-reading.
  3. Answer the interview questions out loud, as if to an interviewer, and only then compare with the model answer.
  4. A week later, redo the flashcards. Mark the chapter as done once they feel easy.

Your progress (chapters done, known flashcards) is saved in this browser only.

How interviewers use OS questions ​

At senior level, OS questions rarely stop at definitions. Expect a chain like:

"What's virtual memory?" → "What happens on a TLB miss?" → "Your service's p99 latency doubled after moving to bigger machines. Could memory management be involved? How would you check?"

So for every concept, aim to be able to explain what it is, what it costs, and when it becomes a problem in production.