Networking and OS Conceptual Interview Questions: TCP, Processes, Memory, and Concurrency

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## Problem

A set of conceptual questions covering networking and operating systems fundamentals, as asked in onsite and phone screens.

**Networking:**
- Walk through the full lifecycle of an HTTP request from typing a URL to receiving HTML. Name every protocol involved.
- What happens during a TCP 3-way handshake? What state is the server socket in before and after?
- Explain the difference between TCP and UDP. When would you choose UDP for a production system?
- What is a TIME_WAIT state and why does it exist? How can it cause port exhaustion?

**Operating Systems:**
- What is the difference between a process and a thread? What is shared vs isolated between threads in the same process?
- Describe virtual memory. Why can two processes both "have" address 0x1000 without conflicting?
- What is a context switch, what triggers it, and what does the OS save/restore?
- Explain the difference between a mutex and a semaphore. Give a scenario where each is the right choice.

## Follow-ups

1. If `ping` succeeds but HTTP fails to the same host, what are the possible causes?
2. You have a program that runs fine single-threaded but crashes intermittently with multiple threads. What tools and techniques do you use to diagnose it?
3. Explain copy-on-write (COW) in the context of `fork()`. Why is it an optimization?
4. What is a page fault, and when is it a problem vs expected behavior?

Networking and OS Conceptual Interview Questions: TCP, Processes, Memory, and Concurrency

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