Operating System Interview Questions - Common & Advanced Topics

Efficient CPU scheduling is at the core of elevating the performance level of a system and optimizing resource utilization in an operating system. Scheduling algorithms decide the order of execution of processes on the CPU, thus they are the main factors for system responsiveness, throughput, and fairness. 

Objectives of CPU Scheduling

The main goals of CPU scheduling are to keep the CPU busy as much as possible, reduce the waiting and turnaround times, and ensure that all processes get fair treatment. Load balancing at its best contributes to the even distribution of workloads over the system ​‍​‌‍​‍‌​‍​‌‍​‍‌resources. 

Types of Scheduling Algorithms

Several CPU scheduling algorithms are used, each with distinct strategies:

• First-Come, First-Served (FCFS) Scheduling: Processes are scheduled in the order they arrive. FCFS is simple and non-preemptive, but it may lead to longer waiting times for short processes if a long process arrives first.
• Shortest Job Next (SJN): Also known as Shortest Job First (SJF), this non-preemptive algorithm selects the process with the shortest burst time for execution next. While it can minimize average waiting time, it requires knowledge of burst times in advance.
• Priority Scheduling: Each process is assigned a priority, and the scheduler selects the process with the highest priority. Priority scheduling can be preemptive or non-preemptive. Lower-priority processes risk starvation if higher-priority processes consume the majority of the CPU's resources.
• Round-Robin (RR) Scheduling: In this preemptive algorithm, each process receives a fixed time slice (quantum) in a cyclic order. Round Robin is a fair and responsive algorithm, making it suitable for time-sharing systems.
• Multilevel Queue Scheduling: Processes are grouped into separate queues based on characteristics (e.g., foreground and background jobs), and each queue can use a different scheduling algorithm. The dispatcher module manages transitions between queues and processes.

Preemptive vs. Non-Preemptive Scheduling

• Preemptive Scheduling: The operating system can interrupt a running process to switch to another, allowing higher-priority or ready processes to be executed promptly. This improves responsiveness but increases the overhead of context switching.
• Non-Preemptive Scheduling: Once a process starts executing, it continues to run to completion or until it voluntarily yields the CPU. This method is simpler but can lead to longer wait times for other processes.

Related Concepts

• Context Switching: When the CPU switches from one process to another, it saves the current process state and loads the next. Frequent context switching can increase overhead and reduce efficiency.
• Dispatch Latency: The time it takes for the dispatcher module to stop one process and start another is called dispatch latency. Minimizing dispatch latency helps improve system responsiveness.
• Burst Time: Burst time refers to the total time a process requires on the CPU for execution. Scheduling algorithms often use burst time to make decisions.
• Load Balancing: Distributing processes evenly across CPUs or cores (in multiprocessor systems) to prevent any single CPU from becoming a bottleneck.

Key Takeaways So Far

• RR guarantees bounded waiting with proper quantum.
• SJF optimal but impractical (burst prediction needed).
• Aging solves starvation in priority scheduling.

These advanced interview questions for os examine more in-depth concepts related to basic operating system interview questions and focus on how they function and manage resources efficiently.

25. What is the exec() system call?

The exec() system call replaces the memory space of a running process with a new program. It is commonly used after a process is created using the fork() function. The new program is specified as a parameter in the exec() call, and once executed, it replaces the existing process image.

26. What is the wait() system call?

A parent process uses the wait() system call to pause its execution until a child process finishes running. Once the child process terminates, the parent receives its process ID (PID) and exit status. This helps in proper process synchronization and prevents orphan processes.

27. What are the advantages of a multiprocessor operating system?

Multiprocessor OS enables a system to run faster by the use of multiple CPUs. Some of the most significant benefits are:

• High Throughput: The total output is greatly increased as several processors are able to work in parallel.
• More Reliability: When a processor unit is faulty, the others can continue the execution, thus, the system becomes more stable.
• Cost Effectiveness: Paying multiple processors to work inside one machine rather than many separate machines can be a more economical solution. 

28. What is a real-time system?

A real-time system processes tasks within a strict time frame. It is used in applications where timely execution is necessary, such as medical devices, automotive control systems, and industrial automation. These systems adhere to predefined time constraints to ensure predictable performance.

29. What is a socket?

Real-time system is a computerized system that can handle requests that come with a specified time limit. It finds its place where execution in time is of the utmost importance such as in medical instruments, automotive control systems, and industrial automation. These systems are bound to meet their deadlines to guarantee performance that can be ​‍​‌‍​‍‌​‍​‌‍​‍‌forecasted. 

30. What is starvation in an operating system?

Starvation occurs when a process waits indefinitely for resources because other processes with higher priority keep getting access first. To prevent starvation, scheduling techniques such as ageing gradually increase the priority of waiting processes, ensuring they eventually receive the required resources.

31. What are the benefits of multithreaded programming?

Multithreading allows multiple threads to run within a single process, which shows several advantages:

• Better Concurrency: Multiple tasks can be executed simultaneously, improving performance.
• Efficient Resource Utilization: Threads share resources, reducing overhead.
• Improved Responsiveness: Applications remain responsive even while executing background tasks.

32. What is the difference between logical and physical address space?

• Logical Address: Generated by the CPU and used by programs during execution.
• Physical Address: The actual location in memory where data is stored.

The OS translates logical addresses into physical addresses using memory management techniques like paging and segmentation.

33. What are overlays in an operating system?

Overlays enable programs that exceed available memory to run efficiently. This technique loads only the necessary parts of a program into memory while keeping the rest on disk. It helps optimize memory usage in constrained environments.

34. What functions are provided by Process Control and File Management system calls?

• Process Control System Calls: This handles process creation, termination, and management.
• File Management System Calls: It enables file creation, deletion, reading, writing, and modification.

Key Takeaways So Far

• Virtual memory uses disk as RAM extension via demand paging.
• Internal fragmentation in paging, external in segmentation.
• Thrashing fixed by increasing RAM or reducing multiprogramming degree.

Modern operating systems must manage multiple processes that compete for shared resources. Two key challenges in this area are preventing deadlocks and ensuring proper synchronization.

Deadlocks

A deadlock occurs when two or more processes are unable to proceed because each is waiting for a resource held by the other. Four necessary conditions must be present for a deadlock to occur:

• Mutual Exclusion: At least one resource must be held in a non-shareable mode.
• Hold and Wait: Processes holding resources can request additional resources held by others.
• No Preemption: Resources cannot be forcibly taken away from a process; they must be released voluntarily.
• Circular Wait: A closed chain of processes exists, where each process holds at least one resource needed by the following process in the chain.

Deadlock Prevention, Avoidance, Detection, and Recovery

• Deadlock Prevention: Techniques that ensure at least one of the four deadlock conditions never occurs. For example, preventing hold and wait by requiring processes to request all resources at once.
• Deadlock Avoidance: The system dynamically examines resource allocation to ensure it never enters an unsafe state. The Banker’s Algorithm is a classic example, granting resource requests only if they keep the system in a safe state.
• Deadlock Detection: The OS can allow deadlocks to occur, but periodically checks for them using detection algorithms. Once detected, the system can recover by terminating processes or preempting resources.
• Deadlock Recovery: Strategies to resolve deadlocks include killing one or more processes or forcefully reclaiming resources.

Synchronization Techniques

In​‍​‌‍​‍‌​‍​‌‍​‍‌ order to keep data consistent and avoid race conditions, several synchronization mechanisms are used:

• Semaphores: These are integer variables that are utilized to indicate and regulate the access to shared resources, thus they are the means by which mutual exclusion is achieved.
• Mutexes: They are locks which enable only one process or thread to have access to the critical section at a time.
• Monitors: Advanced synchronization constructs which comprise shared variables, procedures, and the locking mechanism.
• Inter-Process Communication (IPC) Mechanisms: Such as message passing and shared memory, these are methods that make communication between processes safe and ​‍​‌‍​‍‌​‍​‌‍​‍‌secure.

Resource Allocation and Safe State

Proper resource allocation is crucial for both deadlock avoidance and synchronization. A safe state is a situation where the system can allocate resources to every process in some order without leading to a deadlock.

Key Takeaways So Far

• Banker’s ensures safe state before granting resources.
• Deadlock prevention > avoidance > detection in cost.
• Classic problem: Dining Philosophers tests synchronization mastery.

File and storage management is a core responsibility of modern operating systems, ensuring that data is stored, retrieved, and protected efficiently. This area covers file systems, storage allocation methods, redundancy strategies, and the mechanisms that optimize data access and reliability.

File Systems and File Operations

A file system organises and manages the storage and retrieval of data on storage devices. It provides a structure for storing files, directories, and metadata, enabling operations such as creation, deletion, reading, writing, and modification.

File Allocation Methods

The way files are stored on disk affects performance and reliability. One common approach is the File Allocation Table (FAT), which tracks the location of each file’s data blocks or clusters on the disk. Clusters are the fundamental units of disk storage, and efficient allocation helps minimise fragmentation and improve access speed.

Access Methods

• Direct​‍​‌‍​‍‌​‍​‌‍​‍‌ Access Method: Using this method, data can be read or written directly from or to a unit on a storage device without going through a sequential read.
• Spooling: (Simultaneous Peripheral Operations Online) It stores the data temporarily in a buffer or a queue before sending it to a slower device (like a printer). The system can, therefore, handle multiple I/O requests concurrently.

Storage Management Concepts

• Buffer: A temporary memory area that is used to hold data which is being transferred between two locations. Buffers help devices to work at different speeds, for example, between a fast CPU and a slower disk.
• Caching: It is a method whereby the data which is accessed most frequently is stored in a special, faster storage area so that the access times are reduced and the system performance is improved.
• Access Control: The mechanisms that limit file access depending on user permission, thus securing data and maintaining its ​‍​‌‍​‍‌​‍​‌‍​‍‌integrity.

RAID and Redundancy

RAID​‍​‌‍​‍‌​‍​‌‍​‍‌ (Redundant Array of Independent Disks) is a method that links several physical disks together to form a single logical unit with features like increased performance, larger storage capacity, and data redundancy. Some of the common RAID concepts are:

• Data Striping: Dividing data among several disks for faster read/write ​‍​‌‍​‍‌​‍​‌‍​‍‌operations.

• Mirroring: Storing identical copies of data on two or more disks for fault tolerance.
• Redundancy: Ensuring data remains available even if one or more disks fail.

Bottom Line: RAID levels, such as RAID 0 (striping), RAID 1 (mirroring), and RAID 5 (striping with parity), offer different balances of performance, capacity, and fault tolerance.

35. What is a deadlock?

A deadlock happens when two or more processes get stuck indefinitely because each is waiting for the other to release a resource. Since none of them can proceed, the system reaches a standstill.

36. What is a time-sharing system?

A time-sharing system is a type of multitasking operating system that quickly switches between multiple users, giving each a short time slice to execute their tasks. This creates the illusion that all users are working. Time-sharing systems are crucial when preparing for Operating System Interview Questions, as they are an essential concept in modern computing.

37. How does a monolithic kernel differ from a microkernel?

A monolithic kernel keeps all essential operating system services, such as memory management, file system, and device drivers, within the kernel itself. This results in faster performance but can make debugging and updates more complex.

A microkernel, on the other hand, only contains the core functionalities, like inter-process communication and basic scheduling. Other services run in user space, making the system more modular and secure but slightly slower due to increased communication overhead.

38. What is context switching?

Context switching is when the CPU saves the state of a running process and loads the state of another process. This allows multiple processes to share the CPU efficiently. It occurs in multitasking environments whenever the OS needs to switch from one method to another.

39. What is an interrupt, and why is it important?

An interrupt is a signal sent to the processor to indicate that an urgent event needs attention. It helps the OS prioritise important tasks, such as responding to user input or handling hardware failures, without constantly checking for these events.

40. What are the different memory management techniques?

Operating systems use various memory management techniques to allocate and optimise memory:

• Paging: It divides memory into fixed-size blocks (pages) and maps them to physical memory locations.
• Segmentation: It divides memory into variable-sized sections (segments) based on logical program structures.
• Virtual Memory: Utilises disk space as an extension of RAM, enabling programs to run even when they exceed the available physical memory.

41. What is thrashing, and how can it be prevented?

Thrashing occurs when a system spends more time swapping data between RAM and disk (paging) than executing actual processes. This happens when there isn’t enough RAM, resulting in excessive page faults. To prevent thrashing, you can:

• Increase physical memory (RAM).
• Use more effective page replacement algorithms, such as LRU (Least Recently Used).
• Adjust the number of processes running simultaneously to reduce memory pressure.

42. What is a race condition?

A race condition occurs when multiple processes access and modify shared data simultaneously, leading to unpredictable results. This happens in concurrent programming when proper synchronisation mechanisms are not employed.

43. What is the Banker's Algorithm, and how does it help in resource allocation?

The Banker's Algorithm is a method used to prevent deadlocks by ensuring that resource allocation remains in a safe state. It is a common topic in Operating System Interview Questions. Before assigning resources to a process, the algorithm checks whether it is still possible to meet the needs of all processes without encountering a deadlock. If granting resources could cause a deadlock, the request is rejected or delayed.

44. How do preemptive and non-preemptive scheduling differ?

• Preemptive scheduling: The OS can interrupt a running process and switch to another method if needed. This approach is used in real-time and multitasking systems to improve responsiveness.
• Non-preemptive scheduling: Once a process starts running, it continues until it finishes or voluntarily releases the CPU. This method is simpler but can cause long wait times if a process takes too long to complete.

45. What is the difference between multitasking and multiprocessing OS?

The table below compares how multitasking and multiprocessing operating systems manage processes:

46. Explain zombie processes?

A zombie process is a process that has completed execution but remains in the process table because its parent has not read its exit status.

• It is also referred to as a defunct process.
  
• It does not use CPU or memory, except for its process table entry.
  
• Occurs when the parent process doesn't call wait() to collect the child's status.

47. What is Reentrancy?

Reentrancy refers to code or functions that can be safely executed by multiple tasks or interrupt routines simultaneously without causing conflicts.

A reentrant function:

• Does not use shared or static data.
• Does not modify its own code.
• Uses local variables only.

Used in OS kernels, interrupt handlers, and multithreading for safety.

Key Takeaways So Far

• Indexed allocation solves linked list traversal issue.
• RAID 5 uses distributed parity; can survive one disk failure.
• Spooling enables multitasking with slow peripherals.

Modern operating systems incorporate several advanced concepts to improve efficiency, reliability, and security. Understanding these topics can help you excel in technical interviews that probe beyond the basics.

i) Reentrancy

Reentrancy is a property of code that allows multiple processes or threads to execute the same function simultaneously without causing data corruption or unexpected behaviour. A reentrant function does not modify shared or static data and uses only local variables for its operations. This is especially important in kernel space, where interrupt handlers or concurrent routines may need to call the same function. Reentrant code is essential for safe process management and is widely used in system libraries and OS kernels.

ii) Spooling

Spooling (Simultaneous Peripheral Operations Online) is a technique where data destined for peripherals—such as printers or disk drives—is temporarily stored in a buffer or queue. This allows the operating system to manage scheduling efficiently and prevents slower devices from blocking faster processes. By decoupling the speed of the CPU from that of I/O devices, spooling improves overall system performance and ensures asynchronous operation between components.

iii) Bootstrapping

Bootstrapping is the process that loads the operating system into memory when the computer is powered on. It begins with the power-on self-test (POST), which checks hardware integrity. The system then executes a small program stored in firmware (the bootstrap loader), which loads the OS kernel into memory. This transition from firmware to the whole operating system involves initializing memory allocation, setting up process management structures, and preparing user space and kernel space for operation.

iv) Symmetric Multiprocessing (SMP)

SMP​‍​‌‍​‍‌​‍​‌‍​‍‌ is an architecture wherein two or more processors utilize a shared memory and run under a single OS instance. Any processor can utilize the system resources, such as the memory and the I/O devices, in parallel to each other as the processors have equal access to them. The OS’s scheduling algorithms take the different work units and assign them to different CPUs thus resulting in increased throughput, reliability, and responsiveness. To achieve optimal performance, SMP systems must be highly efficient in memory allocation and process management.

v) System Performance Metrics

To​‍​‌‍​‍‌​‍​‌‍​‍‌ keep and improve efficiency, operating systems also use very detailed measures such as CPU utilization, memory usage, disk I/O rates, and process scheduling efficiency. Access-control lists and user-allowed permissions are mechanisms that help secure resource usage, whereas transmission isolation is used to protect data transfers between the user space and kernel space. Regularly checking these measures gives system administrators the opportunity to identify the limits, use peripherals competently, and implement security policies.

Quick Note: Reentrancy ensures thread-safe code; spooling decouples I/O speed; bootstrapping initializes kernel; SMP enables true parallelism; metrics + access control drive secure, high-performance OS.

48. What is a Real-Time Operating System (RTOS)?

A real-time operating system (RTOS) refers to a specially designed OS that is geared towards the situations where the completion of the tasks within specified time frames is a must. It guarantees the resolutions of the most important issues in a timely manner and thus, is the most suitable choice for the systems whose operation is heavily dependent on time, such as medical devices, industrial automation, embedded systems, etc. 

49. What are the key characteristics of an RTOS?

The features of an RTOS include:

• Deterministic Execution: The system is able to maintain the timing of the process and execution it has foreseen.
• Low Latency: The response to the incoming stimuli is carried out almost at once which makes the time interval between such two actions extremely short.
• High Reliability: The performance of the system is steady and trustworthy even when it is used in the most demanding and critical ​‍​‌‍​‍‌​‍​‌‍​‍‌situations. 

50. What are the different types of RTOS?

RTOS can be classified depending on their deadline enforcement strictness:

• Hard RTOS: It assures that critically required tasks are always performed within time. Failure to meet a deadline can result in system failure. Example: Airbag control systems.
• Soft RTOS: It attempts to meet deadlines but can occasionally postpone tasks without causing any serious effects, such as video streaming.
• Firm RTOS: This closely resembles a hard RTOS except for having more slight flexibility. Infrequent deadline misses are allowed, but a large number of failures will lead t

51. What are the advantages of using an RTOS?

RTOS​‍​‌‍​‍‌​‍​‌‍​‍‌ brings in a number of advantages:

• Timely Task Execution: Mainly it is the feature that assures the performance of the most important tasks within their set time limits.
• Predictable Performance: The main advantage of this feature is stabilizing and making reliable the task scheduling process.
• Efficient Resource Management: With this, CPU, memory, and other hardware resources are used at a high level of ​‍​‌‍​‍‌​‍​‌‍​‍‌efficiency.

52. What are the challenges of using an RTOS?

Instead of its advantages, RTOS comes with some challenges:

• Complexity: Designing and implementing an RTOS-based system requires specialised knowledge and expertise.
• Resource Constraints: RTOS usually runs on hardware with limited processing power and memory, requiring efficient optimization.
• Difficult Debugging: Identifying and fixing real-time execution issues can be more challenging than in traditional systems.

Bottom Line: RTOS ensures timely execution hard deadlines prevent failure soft allows delay offers low latency reliability but needs expertise optimization and complex debugging

When preparing for an Operating System Interview Questions. A solid understanding of operating system topics, as well as an understanding of how operating systems function, helps in answering technical questions effectively. Here are the core areas to study.

1.​‍​‌‍​‍‌​‍​‌‍​‍‌ Process Management

Operating systems are responsible for controlling processes that involve tasks such as creating, running, and deleting processes. Figuratively, processes are said to have three different states: ready, running, and waiting. The operating system uses a Process Control Block (PCB) to keep track of each process. Scheduling algorithms, e.g. First-Come-First-Served (FCFS), Round Robin, and Shortest Job Next (SJN,) are used to decide which method should be given CPU time.

2. Memory Management

Memory management must be highly efficient to prevent programs from crashing and interfering with each other. Operating systems achieve this by means of paging and segmentation techniques. Additionally, virtual memory allows the use of disk space as an extension of RAM, so that the running of large applications will not exhaust the physical memory.

3. File Systems

A file system is a method that helps keep data organized and manageable, which is saved on a disk. It also provides a systematic way to store and fetch files through the use of directories and indexing. Different file systems, including NTFS, FAT32, and ext4, differ regarding their structures and features. Primary file operations include reading, writing, creating, and deleting a file.

4. Concurrency and Synchronization

Through multiprogramming, current operating systems are capable of carrying out multiple tasks concurrently, rendering the management of concurrency a must-have skill. To ensure data consistency when a shared resource is accessed by various processes synchronization tools, such as semaphores, mutexes, and condition variables are employed. Deadlocks, which occur when processes wait for each other and thus come to a halt, can be prevented or resolved using methods such as resource ordering and the banker’s algorithm.

5. I/O Management

The CPU sends I/O commands to other peripheral devices, such as printers, disk drives, and keyboards. An operating system manages input/output (I/O) devices by utilising device drivers and scheduling methods. Polling, interrupts, and Direct Memory Access (DMA) are the different techniques used to handle I/O requests in efficient manners.

6. Security

An operating system helps ensure security by letting in only authorized users, thus, unauthorized ones not being able to access confidential data or interfere with the operations of the system. Security provisions that are actively implemented include access control, credential verification, and permission granting. Firewalls, encryption methods, and intrusion detection systems are the ways that protect users from cyber threats.

7. Virtualization

Virtualisation is a technology that enables multiple operating systems to run on a single physical machine by utilising virtual machines. The management of the different VMs is performed by a hypervisor that serves as an abstraction layer between hardware and software. Virtualization raises resource efficiency, bolsters security, and makes possible cloud computing. Apart from that, virtualization is also a significant topic in operating system interviews.

8. Real-Time Systems

Real-time operating systems or just RTOS are found in scenarios where the execution of the tasks should be on time at any cost. Examples are medical equipment, automotive systems, and industrial automation. RTOS strictly adhere to scheduling algorithms such as Rate Monotonic Scheduling (RMS) and Earliest Deadline First (EDF) to make sure the execution of time-critical tasks is done on time.

9. Distributed Systems

A distributed system is a collection of separate computers that collaborate for the production of a service. These systems communicate with each other via client-server and peer-to-peer models. Distributed file systems, fault-tolerance mechanisms, and distributed synchronisation techniques facilitate the management of resources spread across various nodes.

10. Kernel Architecture

The kernel is basically a single unit that is made up of various components and is the main part responsible for handling the hardware and the rest of the system resources of the OS. System calls are the main functions that the kernel is in charge of executing, thus enabling user apps to function in hardware interaction. Besides that, the kernel management stack also features memory management, process management, file systems, and device drivers. Types of kernel designs range from monolithic kernels, microkernels, and hybrid kernels to name a few with each set having its own pros and ​‍​‌‍​‍‌​‍​‌‍​‍‌cons.

Preparing for operating system interview questions requires a solid understanding of core concepts and consistent practice in answering questions and solving problems. Begin by reviewing the fundamentals, ensuring you have a clear understanding of concepts such as process management, memory management, and file systems.

Practicing OS-related questions from basic to advanced helps in strengthening problem-solving skills. Try to include real-world examples to indicate your understanding of concepts like scheduling algorithms, deadlock prevention, and virtualization. Utilizing online resources, such as tutorials, articles, and discussion forums, can also supplement your learning and clarify complex topics.

Mock interviews with friends or colleagues are a great way to simulate a real interview environment and receive constructive feedback. Staying updated on the latest OS developments and related technologies can also give you an edge. During the interview, remain calm, confident, and focused.

Key Takeaways So Far

• RTOS prioritizes deterministic timing over throughput.
• Reentrant code uses only stack variables—no static/global modification.
• Type-1 hypervisors more efficient and secure than Type-2.

To succeed in computer science or IT, you need a strong grasp of operating systems, which will help you build a solid understanding. Studying Operating System Interview Questions can enhance your preparation by covering key areas like process management, memory management, and real-time systems. With consistent practice, you'll gain the confidence to showcase your skills effectively.

Why It Matters?

Operating Systems control every device and cloud service in 2025. Mastering OS concepts is mandatory for high-paying roles in systems programming, cloud infrastructure, embedded/RTOS, kernel development, and BigTech interviews (Google, Meta, Apple) where OS questions decide offers and packages above $150K–$300K.

Practical Advice for Learners

• Draw process state diagram and PCB structure daily for 2 weeks.
• Solve 50+ scheduling problems with Gantt charts and calculations.
• Implement semaphore solutions to classic problems (producer-consumer).
• Revise Banker’s algorithm with numerical examples until automatic.
• Practice explaining concepts aloud—interviewers value clarity over complexity.