Operating Systems is a fundamental subject tested in technical interviews at every IT company in 2026, especially at companies like Microsoft, Google, Amazon, and Apple. Whether you're preparing for Systems Engineer, DevOps Engineer, or Software Developer roles, these top 10 OS interview questions are most frequently asked.

Keywords: operating systems interview questions 2026, OS interview, process management interview, memory management interview, deadlock interview questions

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1. What is an operating system and what are its main functions?

An operating system is system software that manages hardware resources and provides services to application programs. Its main functions include process management, memory management, file system management, device management, and providing a user interface. Examples include Windows, Linux, and macOS.

2. What is the difference between a process and a thread?

A process is an independent program in execution with its own memory space. A thread is a lightweight unit of execution within a process that shares the process's memory. Processes are isolated from each other while threads within the same process can communicate easily. Context switching between threads is faster than between processes.

3. What is a deadlock? What are the necessary conditions?

A deadlock occurs when two or more processes are blocked forever, each waiting for a resource held by another. Four necessary conditions are: Mutual Exclusion (resource held exclusively), Hold and Wait (holding one resource while waiting for another), No Preemption (resources cannot be forcibly taken), and Circular Wait (circular chain of waiting processes).

4. Explain process scheduling algorithms.

Key scheduling algorithms include: FCFS (First Come First Served - simple but can cause convoy effect), SJF (Shortest Job First - optimal average waiting time), Round Robin (time quantum based, good for time-sharing), Priority Scheduling (processes executed by priority), and Multilevel Queue (multiple queues with different algorithms).

5. What is virtual memory?

Virtual memory is a memory management technique that gives each process the illusion of having a large contiguous memory space. It uses disk space as an extension of RAM through paging or segmentation. Pages are swapped between RAM and disk as needed. This allows running programs larger than physical memory and improves multitasking.

6. What is the difference between paging and segmentation?

Paging divides memory into fixed-size blocks called pages (physical) and frames (logical), eliminating external fragmentation. Segmentation divides memory into variable-size segments based on logical divisions like code, data, and stack. Paging is invisible to the programmer while segmentation is programmer-visible. Modern systems often use a combination of both.

7. What are semaphores and how do they prevent race conditions?

A semaphore is a synchronization tool used to control access to shared resources. Binary semaphores (mutex) allow only one process at a time. Counting semaphores allow a set number of concurrent accesses. Operations are wait (P) to acquire and signal (V) to release. They prevent race conditions by ensuring mutual exclusion in critical sections.

8. Explain the different types of operating systems.

Types include: Batch OS (jobs processed in batches without interaction), Time-sharing OS (CPU time shared among multiple users), Real-time OS (guaranteed response within deadlines, used in embedded systems), Distributed OS (manages a group of networked computers), and Network OS (provides services to computers on a network).

9. What is thrashing in an operating system?

Thrashing occurs when the system spends more time swapping pages between memory and disk than executing actual processes. It happens when there are too many processes competing for limited physical memory. The CPU utilization drops dramatically. Solutions include reducing the degree of multiprogramming, using working set model, or adding more RAM.

10. What is the difference between user mode and kernel mode?

User mode is a restricted mode where applications run with limited access to hardware and system resources. Kernel mode is a privileged mode where the OS core runs with full access to all hardware and instructions. System calls are used to switch from user mode to kernel mode. This separation protects the system from faulty or malicious user programs.