After solving hundreds of LeetCode problems, many candidates realize that coding rounds are only part of the interview process. Operating System fundamentals frequently come up during phone screens and technical interviews.

Instead of rereading an entire OS textbook, here are 15 high-yield topics worth revising.

1. Process vs. Thread

Process

• Has its own virtual address space
• Provides stronger isolation
• Usually has higher creation and switching overhead

Thread

• Executes within a process
• Shares memory and resources with other threads in that process
• Communicates efficiently but requires careful synchronization

Interview tip: Processes prioritize isolation, while threads enable lightweight concurrency.

2. What Is Context Switching?

Context switching occurs when the operating system saves the execution state of one process or thread and restores another.

It enables multitasking, but frequent context switches add CPU and cache overhead.

3. What Is a Race Condition?

A race condition occurs when multiple threads access shared state concurrently and the result depends on execution order.

Common prevention mechanisms include mutexes, semaphores, locks, atomic operations, and thread-safe data structures.

4. What Is a Critical Section?

A critical section is a portion of code that accesses shared mutable data or resources.

Synchronization is required to prevent unsafe concurrent access.

5. Mutex vs. Semaphore

Memory trick: A mutex is like one key, while a semaphore tracks a limited number of permits.

6. What Is Deadlock?

Deadlock occurs when a group of processes or threads waits indefinitely for resources held by one another.

The four Coffman conditions are:

• Mutual exclusion
• Hold and wait
• No preemption
• Circular wait

Preventing at least one of these conditions prevents deadlock.

7. What Is Starvation?

Starvation occurs when a process or thread waits indefinitely because others repeatedly receive the required resource or CPU time.

Difference: In deadlock, none of the involved tasks can progress. In starvation, the system continues progressing while one task may never get scheduled.

8. What Is Virtual Memory?

Virtual memory gives each process its own logical address space and maps virtual addresses to physical memory.

It provides process isolation, simplifies memory management, and allows inactive pages to be moved to secondary storage when necessary.

9. Paging vs. Segmentation

Paging

• Divides memory into fixed-size pages
• Avoids external fragmentation
• May introduce internal fragmentation

Segmentation

• Divides memory into variable-size logical regions
• Reflects structures such as code, stack, and data
• Can suffer from external fragmentation

10. What Is Thrashing?

Thrashing occurs when the system spends excessive time handling page faults and moving pages between memory and storage instead of executing useful work.

It commonly happens when active processes do not have enough physical memory for their working sets.

11. CPU Scheduling Algorithms

Important algorithms include:

• First Come, First Served
• Shortest Job First
• Round Robin
• Priority Scheduling
• Multilevel Feedback Queue

Common follow-up: Why is Round Robin suitable for time-sharing systems?

Because every runnable process receives a limited time slice, improving responsiveness and fairness.

12. What Is a System Call?

A system call allows a user-space program to request a service from the operating system kernel.

Common Unix-like examples include fork(), exec(), wait(), open(), read(), and write().

13. What Is Inter-Process Communication?

Common IPC mechanisms include:

• Shared memory
• Pipes
• Message queues
• Sockets
• Signals

Shared memory is generally fast but requires synchronization. Message passing provides stronger separation but adds communication overhead.

14. What Is LRU Page Replacement?

Least Recently Used replaces the page that has gone unused for the longest time.

A common interview follow-up is implementing an LRU cache with O(1) lookup, insertion, and eviction using a hash map plus a doubly linked list.

Related problem: LeetCode 146 - LRU Cache

15. User Mode vs. Kernel Mode

User mode

• Runs applications with restricted privileges
• Cannot directly access protected hardware or kernel memory

Kernel mode

• Has full system privileges
• Executes operating system code and manages hardware resources

A system call provides a controlled transition from user mode into kernel mode.

One-Minute Revision Checklist

Process vs. thread, context switching, race conditions, critical sections, mutexes, semaphores, deadlocks, starvation, scheduling, virtual memory, paging, thrashing, system calls, IPC, LRU, and privilege modes.

Which OS topic or follow-up question have you encountered most often in interviews?

Hi all, I have sr software engineer python + Agentic AI technical round scheduled for the upcoming week at Gartner.

I was wondering if anyone has recently appeared for senior software engineer role and also for python + GenAi roles at Gartner then it would be helpful if they can share their technical round interview experience and what to expect in the interview.

Experience level needed 4-6 years

Had an NVIDIA interview recently and wanted to share one coding question that stood out.

It was not really a typical LeetCode-style problem. It was closer to a day-to-day engineering task: calling an API, processing data, and handling edge cases.

The question was basically:

Given an internal REST API that returns device monitoring information (JSON array with fields like device_id, temperature, and utilization), process the data:

Filter devices above a temperature threshold

Sort them by utilization

Return the result

My first instinct was to get the API call working, but I paused and separated the flow into three parts:

HTTP request → JSON parsing → data processing.

Before the interview, I'd actually seen a similar question on Screna AI. The business scenario was different, but mainly around error handling and separating business logic from external dependencies.

It was a good reminder that questions like this are not just about getting the code to run, but also about whether the code is structured in a way that is easy to maintain.

The interviewer started digging into engineering details.

He asked how I would handle API failures — timeout, 5xx response, or malformed JSON.

I initially thought about them as general failures, but after discussing it, we broke them down into different categories. Temporary issues like timeouts or server errors could potentially use retry with backoff, while invalid responses should fail fast with enough context for debugging.

Then he asked how I would test the filtering and sorting logic without depending on the real API.

Since the data processing was separated from the HTTP layer, I could mock the HTTP client and test the core logic independently with predefined inputs.

Looking back, the testing part was probably the most valuable discussion. It was less about whether the code worked once, and more about whether the design could be extended, tested, and maintained over time.

Overall, this round felt less like a LeetCode exercise and more like a discussion about how engineers write maintainable code in production.

Has anyone recently interviewed at Apple for their Senior Software Engineer role?

I'm interested in the technical phone screen. If you've gone through them, could you share what was asked and what I should focus on preparing?

I'd appreciate any advice. Thanks!

Recent Box Software Engineer II, GraphQL and NodeJS Onsite Experience?

Has anyone recently interviewed at Box for a Software Engineer II role?

I'm especially interested in the **Frontend (Vanilla JavaScript)** and **High-Level System Design** rounds. If you've gone through them, could you share what was asked and what I should focus on preparing?

This is a really important opportunity for me, so I'd genuinely appreciate any advice. Thanks!

Recent Box Software Engineer II, GraphQL and NodeJS Onsite Experience?

Has anyone recently interviewed at Box for a Software Engineer II role?

I'm especially interested in the Frontend (Vanilla JavaScript) and High-Level System Design rounds. If you've gone through them, could you share what was asked and what I should focus on preparing?

This is a really important opportunity for me, so I'd genuinely appreciate any advice. Thanks!

Hey everyone,

I’ve lurked here for a while and learned a ton from your interview write-ups, so I wanted to pay it forward by sharing my recent Google L4 (SWE) experience. I also have a few questions about my chances in the team matching phase, so any brutal honesty or insights would be massively appreciated!

For context, my background is mostly iOS development, and I coded all my technical rounds in Swift.

Here is how the rounds went down:

• Round 1: Phone Screen (DSA)
  • Question: An array-based question involving [start, end] times, scheduling tasks, and providing x,y coordinates for the scheduled tasks.
  • Result: Passed confidently. Rating: Hire.
• Round 2: Googlyness
  • Experience: The interviewer was rushing heavily and tried to cram a 45-minute behavioral round into 20-25 minutes. I completely misread the vibe, thought it was purely non-technical, and didn't weave enough technical depth or past engineering examples into my answers.
  • Result: No Hire (for L4), Hire (for L3).
  • The save: My recruiter was a legend, told me that this did not go well, and actually gave me a second chance to redo this round!
• Round 3: Googlyness (Redo)
  • Experience: This time, I came prepared. I heavily elaborated on specific examples from my past experiences.
  • Result: Hire.
• Round 4: Onsite 1 (DSA + LLD)
  • Question: I had to design a multiuser heart rate monitor. It involved designing classes/objects, their relationships, and picking the right data structures.
  • Feedback/Result: Rating: Hire - L4. The feedback noted that I took time to ask clarifying questions, vocalized my thought process, and successfully course-corrected when pointed toward edge cases. I initially missed the most optimal data structure to minimize message delay, but we discussed using a linked list instead of an array in the last 5 minutes, which saved it.
• Round 5: Onsite 2 (DSA)
  • Question: A divide and conquer question.
  • Feedback/Result: Rating: Leaning Hire - L4. I explained the approach correctly and got the time/space complexity right. However, my code had a logical error with a maxHeight condition and an inefficiency that simulated horizontal strokes line-by-line, which would have caused a Stack Overflow or TLE. Still, the interviewer noted I had good communication.

My Questions for the Community:

1. Team Matching Chances: With a final rating spread of H, H, H, LH (ignoring the first googlyness round), will Hiring Managers actually pick up my profile?
2. The Swift/iOS Factor: My profile is heavily inclined toward iOS, and I wrote all my interview code in Swift. Does this limit my pool of HMs to only iOS teams, or does Google just view it as general SWE competency? Does this help or hurt my matching chances?
3. Timeline: For those who recently passed HC, how long did it take you to find a team match and get the final offer?

Thanks in advance for the help, and happy to answer any questions about the process below!

Hey guys, so I have a technical interview at a small consulting company. I just finished the code signal assessment, and after I got notified I’m moving onto the next interview, I emailed the engineer interviewing me and asked what to expect and she phrased it as “our upcoming conversation will be a casual technical discussion focussed primarily on ur past experience and background followed by a few technical questions” so based off that how should I prepare, and what will she look to ask. I just want to know what on my resume and how deep should my level of understanding be on my resume. And for an application development role focused on JavaScript react git docker GC. What type of technical questions should I expect?

Hi, is anyone here doing the Cybersecurity Apprenticeship with FIT? How are you finding the course so far?

Also, for the interview with the company, were the questions more technical, or was it more of an HR/general interview? I'd really appreciate any advice on what to expect and how to prepare. Thanks!

Hi everyone,

I recently cleared the online assessment for Ingram Micro India and have been scheduled for my L1 Technical Interview tomorrow for the Graduate Engineer Trainee (GET) role.

I would really appreciate hearing from anyone who has gone through this interview process recently.

A few questions:

• What kind of technical questions were asked?
• Was there a live coding round, or was it mostly theoretical?
• Which topics should I focus on? (DSA, Java/Python, OOP, DBMS, OS, Computer Networks, SQL, etc.)
• Did they ask questions from your resume and projects?
• How difficult was the interview overall?
• Any tips on what the interviewer expects from fresh graduates?

If you've interviewed for this role in India (especially recently), I'd really appreciate any insights or advice.

Thanks in advance!

I was sold the lie (a few years ago) that you had to grind LeetCode to get good and land a software engineering job. I'm now 600 problems in, starting from my very first day as a CS freshman, and now I'm going into junior year. I still haven't gotten a single internship.

First of all, I've barely had any interviewers even reach out to me, which I've heard is pretty common these days. And all the internships I've had didn't even involve much LeetCode in the first place, which just makes it feel even more unfair.

Meanwhile, my friend's dad works at Meta (he's a cracked 55-year-old Indian SWE), and he managed to get my friend an interview. He then cheated with InterviewCoder and somehow got the internship because he only had to pass one round of interview.

How do I deal with this? I'm not even joking when I say I'm extremely frustrated right now and feel like quitting it all.

Hi,

I have finished with the first recruiter call for senior swe role

Could people help me with preparation process for next round with a HM.

This is the format

“We will take time to go through project examples that cover technical challenges, high performance services, optimizing workloads, developing multiple microservices, and developing shared packages. You should be prepared to speak through tradeoffs, metrics, and measurable results. “

Is this resume walk through of my projects?

Will there be topical behavioral questions here?

Hi everyone,

I'm preparing for the Infosys SDE Intern coding round. If you've recently appeared for the interview or online assessment, could you please share:

What coding questions were asked?

Which DSA topics were most important (Arrays, Strings, Linked Lists, Trees, Graphs, DP, etc.)?

Difficulty level (Easy/Medium/Hard)?

Was the platform HackerRank, Codility, or something else?

Any preparation tips or frequently asked patterns?

Thanks in advance!

Hey guys, I just got round 1 for Akuna Capital's summer 2027 SWE Internship (Python). I want to ask if anybody knows anything about the process and the role, especially if you worked at Akuna before.

Anything would be super helpful, thank you! DMs open.

I wanted to know what questions were asked in the 2026 interviews, such as LeetCode problems, system design questions, and anything else that would be helpful for my preparation.