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The Most Commonly Asked OS Interview Questions

Preparing for an interview about operating systems (OS) can be difficult. OS concepts are fundamental to understanding how software interacts with hardware. The function of operating systems is to manage hardware resources, develop a platform for executing applications and ensure efficient performance of the system. OS subjects are a common focus during technical interviews because they are fundamental to any software development or IT job.

This guide covers essential questions on process management, memory management, file systems as well as security. Additionally, example answers will be provided to help you prepare fully and ensure that you handle questions related to OS effectively during your interview.

Basic-level OS Interview Questions

1.   What is an operating system?

An Operating System is a computer program that controls both the computer hardware devices and software resources. The operating system works between the programs and users of one side and the hardware components of the computer on the other side by offering the common services, which computer programs utilize. Examples include Windows, macOS or Linux.

2.   What are the main functions of an operating system?

The main functions of an operating system include:

3. What are the differences between multiprogramming, multitasking, and multiprocessing?

4. What is a context switch in the Operating System?

Context switch refers to a process whereby CPU state storage is done in such a way that multiple processes are enabled to share a single CPU resource. When context switching takes place, it enables the OS to jump from one task to another, ensuring efficiency in multitasking or execution of other critical functions within a PC system. During the context-switching process, information like registers or program counters would be saved into the process table before being loaded into the new state of the next running process.

5. What is a process and process table?

A process is a program in execution, including its code, data, and resources. It is an active entity with a unique Process ID (PID). The process table is a data structure maintained by the operating system that keeps track of all the processes. It contains information such as the process state, PID, program counter, and memory allocation.

6. What is Thread?

A thread is the smallest unit of a process that can be scheduled and executed by the CPU. It is a path of execution within a process and shares the process’s resources, such as memory and open files. Multiple threads can exist within a single process, enabling parallelism and efficient task management.

7. Explain the difference between a process and a thread.

8. Describe the process of process creation and termination.

Process Creation:

• Forking: The operating system creates a new process by duplicating an existing one.
• Initialization: The new process is initialised with a unique Process ID (PID).
• Resource Allocation: Memory and other resources are allocated.
• Execution: The new process starts executing, either continuing from the point of the original process or beginning a new program.

Process Termination:

• Normal Exit: The process completes its execution and calls an exit system call.
• Error Exit: The process encounters an error and is terminated.
• Forced Termination: Another process or the OS forces the process to terminate using a kill command.
• Resource Deallocation: The OS reclaims the resources used by the process.

9. What is the difference between preemptive and non-preemptive scheduling?

10. What is a system call, and in what ways does it differ from a normal function call?

System Calls:

• System calls are functions available to running programs that enable them to request services from the kernel, such as file operations, process control, and communication.
• They run in kernel mode, which provides them with access to hardware and other resources that are crucial to a system.

Normal Function Calls:

• Normal function calls are user-defined, or library functions that execute within the user program’s context.
• They run in user mode and do not have direct access to hardware or kernel resources.

 11. Differentiate the kernel mode and user mode.

12. What is Thrashing?

Thrashing refers to the constant swapping of pages in and out of memory while the actual processes are not being executed because the system is busy. It normally results from a shortage in RAM, which degrades the performance of a system.

13. What are the benefits of multithreaded programming?

14. What is Buffer?

Any temporary storage section that is used as an intermediate in withholding data during its movement from one location to another is known as a buffer. Buffers are used to manage data streams and improve data transfer efficiency between devices or processes.

15. What is Demand paging?

Demand paging is a memory management technique wherein the memory loads only the pages of data when required instead of loading all pages in advance. Hence, it does not congest the memory and hence speeds up the performance of a system.

16. What are the different states of the process?

17. What are the 5 important concepts of OS?

• Process Management: Handling the creation, scheduling, and termination of processes.
• Memory Management: Managing the allocation and deallocation of memory space.
• File System Management: Organizing, storing, and accessing data on storage devices.
• Security and Access Control: Protecting data and resources from unauthorised access.
• Device Management: Controlling and coordinating hardware devices through drivers.

 18. What are the different scheduling algorithms?

19. Describe the objective of multiprogramming.

The highest utilisation of the CPU by running several processes together is the goal of multiprogramming. In that case, it always keeps the CPU busy with the execution of any process to enhance efficiency and throughput.

20. What problem do we face in computer systems without OS?

Without an OS, computer systems face several problems, including:

• Resource Management: No centralised management of CPU, memory, and I/O devices.
• User Interface: Lack of a user-friendly interface to interact with hardware.
• Security: No protection mechanisms to prevent unauthorised access.
• Program Execution: Difficulties in loading, executing, and managing multiple programs.

21. What is FCFS?

First-Come, First-Served (FCFS) scheduling algorithm executes processes according to their arrival order in the ready queue. It has an easy validation process because it only needs proportionate waiting times, but in some scenarios, it results in a convoy effect, causing slow response due to long tasks with small ones behind them.

22. What is the RR scheduling algorithm?

Round Robin (RR) Scheduling Algorithm allocates a fixed time slot, (Time Quantum) for every process in the ready queue. The CPU cycles through processes giving each one a turn to execute for quantum duration. This ensures fairness, leading to better response time but may result in massive context switching overheads.

23. What is cache?

Caching is the process of putting frequently used data in a temporary storage area to make access to data more rapid. This latency-reducing and performance-enhancing function can be found either at higher or lower levels of computing.

24. What is the functionality of an Assembler?

An assembler translates assembly language into machine code that a computer’s CPU can directly execute. This allows us to use mnemonics and symbols that are later translated to the corresponding binary opcode and addresses, making low-level programming possible.

25. What does GUI mean?

A graphical user interface, or GUI, is a computer environment wherein a human can interact with the computers through windows, icons, buttons, and menus-instead of typing command lines. GUIs make software more usable and accessible by providing intuitive graphical controls that allow users to quickly painlessly complete their intended tasks.

26. What is a pipe? When Is It Used?

Pipes use unidirectional flow when passing information from one process to another in inter-process communication. Pipes are commonly used for connecting the output from one process to the input of another thus enabling sharing of data and task chaining in an efficient manner.

27. What are the goals of CPU scheduling?

28. Write the name of synchronisation techniques.

• Mutexes (Mutual Exclusion)
• Semaphores
• Monitors
• Spinlocks
• Barriers
• Condition Variables

29. Define the term Bit-Vector.

A bit vector is a vector in which each element is a bit – thus, its value is either 0 or 1. In most vectors, each element is in a distinct address in memory and can be manipulated independently from the rest of the elements, and we also hope to be able to perform “vector operations” that treat all elements uniformly. One application of bit vectors is in encoding information in a computer system; for example, numbers are represented using bit vectors.

30. Write the names of different operations on the file.

• Create
• Open
• Read
• Write
• Close
• Delete
• Append
• Rename

31. What is rotational latency?

Rotational latency is the delay experienced while waiting for the desired disk sector to rotate under the read/write head. It is a component of the total disk access time, along with seek time and data transfer time.

32. What is a File allocation table?

A File Allocation Table (FAT) is a file system structure used to keep track of the clusters (storage units) on a disk. It maps each file to its corresponding clusters, allowing the system to locate and manage files efficiently. FAT is used in various file systems, including FAT12, FAT16, and FAT32.

33. How to recover from a deadlock?

34. Definition of real-time systems

Real-time systems refer to computer systems that must respond quickly and precisely at times dictated by external events. Such systems are meant for processing data within hard constraints with regard to timing, they are popularly used in areas like embedded systems, industrial control, mission-critical tasks etc.

35. What is seek time?

Seek time is the duration that a hard disk drive (HDD) takes to find and move a read or write head from one track to another where necessary data has been stored. It contributes significantly to the performance of hard disk access as its value forms a part of the total disk access time.

Intermediate-level OS Interview Questions

36. What are the different RAID levels?

37. Explain Banker’s algorithm.

Banker’s algorithm is a deadlock-avoidance algorithm. It allocates resources based on resource needs of each process, then determines if the state is safe in terms of deadlock avoidance. If the system remains in safe state after allocation, the resources are allocated; otherwise make it wait.

38. What are the Benefits of Dynamic Loading Concerning Better Memory Space Utilisation?

Dynamic loading loads a program’s parts into memory only when they are needed, rather than loading the entire program at once. This reduces the amount of RAM consumed by any specific program at any given moment and allows more simultaneous loading of programs.

39. Explain the main difference between logical and physical address space.

40. What are overlays?

Overlays are mechanisms used to work around physical memory limitations within systems by loading only relevant instructions and data segments into memory. Whenever some different portion of this program may be needed, the current overlay is replaced with the required one. By using this technique, large-sized applications can run on low-memory systems without compromising their functionality at all.

41. What is fragmentation?

Fragmentation occurs when memory is allocated and deallocated in a way that leaves small, unusable gaps. It comes in two types:

42. What is the basic function of paging?

It is a memory management technique that divides a process’s memory into pages that have fixed sizes and physical memory into frames with similar sizes. The functionality of paging provides a way to connect virtual addresses to physical addresses, thereby making it possible for computer systems to use memory in an efficient manner without the need for contiguous allocation.

43. How does swapping result in better memory management?

Swapping improves memory management by temporarily moving inactive processes from the main memory to a storage device (swap space). This frees up RAM for active processes, allowing the system to handle more processes concurrently and improve overall performance. When the swapped-out process is needed again, it is swapped back into memory.

44. What is the Direct Access Method?

The Direct Access Method allows data to be read or written directly to a specific location on a storage device without sequentially accessing preceding data. This method is commonly used in disk drives where each block or sector has a unique address, enabling quick access to data and improving performance for large data sets.

45. When does thrashing occur?

Generally, thrashing occurs when the computer system spends more of its time paging-that is swapping data in and out of memory rather than actually executing any processes. This can be due to a shortage of available RAM, given that heavy paging drastically reduces the performance of the system.

46. What are interrupts?

Interrupts mean signals that are sent to CPU by software or hardware, indicating an event which needs immediate attention. When an interrupt takes place, the CPU temporarily stops executing current instructions and transfers control to an interrupt handler to address the event. After handling the interrupt, the CPU resumes its normal execution.

47. What is Preemptive Multitasking?

Preemptive multitasking is one of the methods used to schedule a central processing unit. In this technique, the operating system allots CPU time for the processes and can forcefully remove a process from the CPU when it is actually allotting another process’s time. This technique guarantees an equal share of CPU time for all the processes and enhances the response of this system by disallowing one process to hold the CPU fully.

48. What are the advantages of semaphores?

49. IPC is what?

Inter-process Communication (IPC) is a method through which several processes communicate with each other and, at the same time, synchronise their actions. Some of these are message passing, shared memory, semaphores, pipes, etc., that allow sharing of the data and thus synchronisation amongst all these diverse processes.

50. What is a Batch Operating System?

A Batch Operating System processes batches of jobs with similar requirements together, without user interaction during execution. Jobs are collected, grouped, and processed sequentially, improving resource utilisation and throughput.

51. What are starvation and ageing in the OS?

52. What is PCB?

A Process Control Block (PCB) is a data structure used by the operating system to store information about a process. The PCB contains details such as:

53. When is a system in a safe state?

A system is in a safe state if there exists a sequence of processes such that each process can be allocated the necessary resources and complete its execution without causing a deadlock. In a safe state, the system can avoid deadlock by careful resource allocation.

54. What is Cycle Stealing?

Cycle stealing entails Direct Memory Access (DMA) controllers transferring data between memory and I/O devices directly by ‘stealing’ CPU cycles. During cycle stealing, the DMA controller gains access to memory while momentarily halting the operation of the Central Processing Unit, thereby reducing its workloads in many cases related to data transfer operations.

55. What are Trap and Trapdoor?

56. What does the dispatcher imply?

Dispatcher is a component of the CPU scheduler that transfers control over CPU selection made by the scheduler itself. The dispatcher performs context switching, i.e., changing the CPU from one process to another selected process and ensuring the selected process starts execution.

57. What is the Locality of reference?

Locality of reference refers to the tendency of a program to access a relatively small set of memory locations repeatedly over a short period. It is divided into two types:

58. How do we calculate performance in virtual memory?

Performance in virtual memory is calculated by evaluating the following factors:

59. What is reentrancy?

Reentrancy refers to the ability of a program or function to be safely interrupted and called again (“re-entered”) before its previous executions are complete. Reentrant code does not rely on shared data and uses local variables, allowing multiple instances to execute concurrently without causing conflicts.

60. Write the top 10 examples of OS.

• Operating System
• Windows 10
• Windows 11
• macOS
• Linux (Ubuntu)
• Linux (Fedora)
• Linux (Debian)
• Android
• iOS
• FreeBSD
• Chrome OS

61. What are the different types of Kernel?

62. What do you mean by Semaphore in OS? Why is it used?

Semaphore is a synchronisation variable that controls the number of processes that can access some common resource in a concurrent system. Basically, it’s an integer variable that could be increased or decreased due to the request of a process. Semaphores are majorly used to combat the problems of critical section and race conditions, as they ensure proper and secure access of shared resources.

63. What are the main functions of Kernel?

64. Write the difference between a microkernel and a monolithic kernel.

65. What does SMP mean (Symmetric Multiprocessing)?

Symmetric multiprocessing (SMP) can be defined as an architecture in which one common memory exists with multiple processors operating under one operating system instance. For each processor, it has equal access towards memory as well as I/O devices such that multitasking applications have parallel processing, resulting in better performance.

66. What is the time-sharing system?

Time-sharing allows several users or tasks to share the same system resources at once by switching between them quickly. Each user or task is given a short amount of time for their execution which gives the impression of having many processes running at the same time thus increasing the general performance and responsiveness of the systems.

67. What are the benefits and disadvantages of a Batch Operating System?

68. What is a bootstrap program in the OS?

A bootstrap program is the very first code that gets executed after a computer is started or reset. It has to initialise the hardware and do any other preparation necessary to make the environment run an operating system, which then also reads the OS kernel from disk into memory. A bootstrap program resides in the computer’s firmware (e.g., BIOS or UEFI)computer’s, which may be implemented in various ways depending on the computer design.

69. What are the different IPC mechanisms?

70. Which thing means deadlock in OS?

Deadlock takes place when there exist some processes that cannot go forward because every process waits for another process among this set holding a resource they need. Consequently, no single process can complete its execution, leading to the halting of the entire system. Deadlocks mainly involve four conditions: mutual exclusion, hold and wait, no preemption, and circular wait.

71. What do you mean by Belady’s Anomaly?

Belady’s Anomaly is a phenomenon in some page replacement algorithms where increasing the number of page frames results in an increase in the number of page faults. It occurs in algorithms like FIFO (First-In, First-Out), where more memory can paradoxically lead to worse performance due to suboptimal page replacement decisions.

72. What is spooling in the operating system?

Spooling (simultaneous peripheral operations online) is a technique where data is held temporarily in a buffer so that it can be used and executed by another device or program later on. This method is often employed for print management purposes whereby documents are spooled to disk or memory and lined up for printing, freeing up CPU cycles so that it can perform other tasks.

73. Where is the Batch Operating System used in Real Life?

Batch Operating Systems are used in environments where large volumes of similar jobs are processed without user interaction. Real-life applications include:

• Payroll Systems: Processing employee salaries and benefits.
• Banking Systems: Handling end-of-day transactions and updates.
• Scientific Computation: Running extensive calculations and simulations.
• Data Processing: Large-scale data analysis and reporting.

74. What are Monitors in the Context of Operating Systems?

Monitors are high-level synchronisation constructs used to control access to shared resources in concurrent programming. They combine mutual exclusion (mutex) and condition variables to manage the safe execution of code blocks by allowing only one process or thread to execute within the monitor at a time.

75. What is a zombie process?

A zombie process is a process that has completed execution but still has an entry in the process table. This occurs when the process’s parent has not read its exit status using the wait() system call. Zombie processes occupy a slot in the process table but do not consume system resources.

Conclusion

Understanding concepts in an operating system will definitely raise the bar during technical interviews, providing you with a leading edge in the field of software development and IT. In this tutorial, you have learned process management, memory management, file systems, and security, all very important concepts that form the basis for undertaking questions related to operating systems. This helps a lot in enhancing problem-solving skills and showcasing technical strengths to prospective hiring companies.

The following questions are practice sets for you. Afterwards, apply these to real situations and continue to study for your interview. Thorough preparation and a solid operating systems knowledge base will give you the confidence to handle tough interview questions and further your career in technology.