An operating system (OS) is software that manages hardware, memory, processes, files, and applications. It also gives users and programs a platform to work on. The following Operating Systems Interview Questions and Answers for 2026 cover important OS concepts, Linux basics, process management, scheduling, memory management, deadlocks, and other topics that often come up in technical interviews.
Here are 20 important OS interview questions and answers that are commonly asked. The questions are split into two sections:
Operating System Interview Questions (Basic)
The first section covers basic operating system interview questions and answers.
Q1. Explain the Bootstrap program and the process to boot the system.
Answer:
Booting is the process of starting a computer by loading the kernel. When a user logs in for the first time, an initial program must run. This program, called the bootstrap program, tells the system what to do at startup. It is stored in read-only memory or EEPROM (electrically erasable programmable read-only memory). The bootstrap program finds the kernel, loads it into main memory, and starts it.
Q2. What are the processes and process tables? Explain the different states through which the process goes.
Answer:
A process is a program that is currently running. Examples include a web browser or a shell script. The operating system manages all these processes, giving each one time to run and allocating resources like memory and disk space. To keep track of them, the operating system uses a process table. This table stores details about each process, such as the resources it uses and its current state.
These processes can be in three states:
- Running: A process is in this state when it has all the resources it needs for execution and permission from the operating system to use the processor. Only one process can be in the running state at a time.
- Ready: A process is in the ready state when it is waiting for the operating system’s permission to use the processor.
- Waiting: Remaining processes can be in a waiting state, awaiting an external event or user input.
Now, let’s move on to the next OS interview questions.
Q3. What is RAID, and what are its different levels?
Answer:
RAID stands for Redundant Array of Independent Disks. It improves overall performance by storing data in multiple places so it can be used when needed.
Here are the different RAID levels:
- RAID 0 – Striped Disk Array without fault tolerance
- RAID 1 – Mirroring and duplexing
- RAID 2 – Memory-style error-correcting codes
- RAID 3 – Bit-interleaved Parity
- RAID 4 – Block-interleaved Parity
- RAID 5 – Block-interleaved distributed Parity
- RAID 6 – P+Q Redundancy
Q4. What are the different types of operating systems?
Answer:
There are five types of operating systems:
- Batch operating system
All jobs are submitted at once and run in a set order. No job can be interrupted until it is finished.
- Multiprogramming operating system
This acts as an extension of the Batch operating system, where the main memory can have several jobs running at once, and they are executed in a particular order at a particular time.
- Multi-tasking operating system
This operating system allows users to run multiple tasks simultaneously on a single processor. The CPU quickly switches between processes to make this possible.
- Multi-processing operating system
This type allows users to run multiple processes simultaneously on a system with multiple CPUs.
- Real-time operating system
In this system, each job is given a set amount of time. Real-time operating systems are often used for critical tasks such as military operations and satellite systems.
Operating System Interview Questions (Advanced)
Next, let’s look at some advanced operating systems interview questions.
Q5. Explain the different kinds of a kernel.
Answer:
There are three main types of kernels:
- Monolithic Kernel:
A monolithic kernel is a full-featured kernel that provides all the core services the system needs.
Example: UNIX
- MicroKernel:
A microkernel provides only the most essential services, with other services running separately.
Example: QNX-real-time OS
- Hybrid Kernel:
It combines aspects of both monolithic and microkernel systems.
Example: Microsoft NT kernel
Q6. Explain the different sections of the process.
Answer:
A process mainly has four sections:
- Stack: Holds local variables and return addresses.
- Heap: Stores dynamically allocated memory using functions like malloc, calloc, or realloc.
- Data: Contains global and static variables.
- Code or text: contains code, program counter, and the content of the processor’s register.
Let’s move on to the next set of operating system interview questions and answers.
Q7. What are the different types of scheduling algorithms?
Answer:
These advanced operating system interview questions are commonly asked. Here are the different types of scheduling algorithms:
- First-come, first-served (FCFS): The first-come process is served first.
- Round Robin (RR): Each process gets a fixed time slice, called a quantum.
- Shortest Job First (SJF): The process with the shortest execution time runs first.
- Priority Scheduling (PS): Each process has a priority value, called the nice value, ranging from 0 (highest) to 99 (lowest). The scheduler picks the process with the highest priority.
Q8. List the different performance metrics for the scheduler.
Answer:
- CPU Utilization: Percentage of time that the CPU is doing useful work (i.e., not being idle). 100% is perfect.
- Wait Time: The time a process spends waiting for its turn to be executed.
- Throughput: The number of processes completed / time unit.
- Response Time: The time elapsed from when a process is submitted until a useful output is obtained.
- Turnaround Time: The time elapsed from when a process is submitted to when it completes.
Q9. What is the Zombie process?
Answer:
A zombie process is a process that has finished executing but still has an entry in the operating system’s process table because its parent process has not yet collected its exit status using the wait() system call. Although the process is no longer running and has released almost all of its resources, a small process table entry remains until the parent acknowledges its termination. If many zombie processes accumulate, they can consume process table entries and may indicate poor process management in an application.
Q10. What is thrashing?
Answer:
Thrashing is a condition in a virtual memory system in which the operating system spends most of its time swapping pages between main memory (RAM) and secondary storage (disk) rather than executing program instructions. It usually occurs when there is insufficient physical memory or too many processes competing for memory, causing a significant drop in system performance. Reducing the number of running processes or increasing RAM can help prevent thrashing.
Q11. What is the difference between a Process and a Thread?
Answer:
A process is an independent program in execution with its own memory space, resources, and process ID. A thread is the smallest unit of execution within a process and shares the process’s memory and resources with other threads. Threads are lightweight, faster to create, and improve application performance through concurrent execution.
Q12. What is Virtualization in an Operating System?
Answer:
Virtualization is the technology that allows multiple virtual machines (VMs) to run on a single physical computer using a hypervisor. Each VM has its own operating system and resources, enabling better hardware utilization, isolation, scalability, and simplified management in cloud environments.
Q13. What is the difference between Virtual Machines and Containers?
Answer:
A Virtual Machine (VM) includes a complete operating system and runs on virtualized hardware through a hypervisor. A container shares the host operating system kernel while isolating applications and their dependencies. Containers start faster, consume fewer resources, and are widely used for cloud-native application deployment.
Q14. What is a System Call?
Answer:
A system call is the interface through which a user program requests services from the operating system kernel. System calls allow applications to perform operations such as file management, process creation, memory allocation, device communication, and network access while ensuring secure interaction with system resources.
Q15. What is a File System?
Answer:
A file system is the method an operating system uses to organize, store, retrieve, and manage files on storage devices. It maintains information about file names, locations, permissions, and metadata. Common file systems include NTFS, FAT32, ext4, APFS, and XFS.
Q16. What is a Race Condition?
Answer:
A race condition occurs when multiple processes or threads access and modify shared data simultaneously without proper synchronization. The final result depends on the order of execution, leading to unpredictable or incorrect outcomes. Synchronization techniques such as mutexes and semaphores are used to prevent race conditions.
Q17. What is Memory Fragmentation?
Answer:
Memory fragmentation occurs when available memory becomes divided into small, unusable blocks, reducing allocation efficiency. External fragmentation occurs with variable-sized memory allocation, while internal fragmentation occurs when allocated memory blocks are larger than required. Techniques such as paging and memory compaction help reduce fragmentation.
Q18. What is Copy-on-Write (CoW)?
Answer:
Copy-on-Write (CoW) is a memory management technique that helps the operating system save memory and improve performance. When a process creates a new process (using fork(), both processes initially share the same memory instead of creating an immediate duplicate. If either process changes the shared data, the operating system creates a separate copy of only that memory page for the process making the change. This avoids unnecessary copying, reduces memory usage, and speeds up process creation.
Q19. What is a Container Runtime?
Answer:
A container runtime is the software that runs and manages containers on a system. It is responsible for downloading container images, creating and starting containers, managing networking and storage, monitoring running processes, and stopping or removing containers when they are no longer needed.
Simply put, a container runtime is the engine that runs containers. Without it, container images cannot be executed. Popular container runtimes include containerd, CRI-O, and Docker Engine, which are widely used in modern environments like Kubernetes.
Q20. How do modern operating systems improve system security?
Answer:
Modern operating systems include many built-in security features to keep computers and user data safe from hackers, viruses, and unauthorized access. Some of the most important security features include:
- Secure Boot: Starts the computer using only trusted software to prevent malware during startup.
- User Authentication: Verifies a user’s identity using a password, PIN, fingerprint, or face recognition.
- Access Control: Allows only authorized users or programs to access specific files and resources.
- Memory Protection: Prevents one program from accessing or changing another program’s memory.
- Address Space Layout Randomization (ASLR): Randomly arranges memory locations to make cyberattacks more difficult.
- Data Execution Prevention (DEP): Stops malicious code from running in protected memory areas.
- Disk Encryption: Encrypts data on the hard drive so unauthorized users cannot read it.
- Sandboxing: Runs applications in an isolated environment to protect the operating system.
- Automatic Security Updates: Regularly installs security patches to protect against the latest threats.
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