Top 70+ Operating System Interview Questions and Answers 2021 [Updated]

By | May 2, 2021
OS Interview Questions

If you are preparing for an IT-based technical interview, then we suggest you go through these best operating system interview questions. In these interviews, apart from your problem-solving skills, the interviewer may also test your knowledge of operating systems.

Every software developer or IT student must have the knowledge and basic understanding of operating systems and the associated terminology.


Candidates who are going to appear for a system administrator (sysadmin) job interview should also have an in-depth understanding of various operating system concepts.

Many aspirants who appear in interviews at Amazon, Google, and other big tech companies also have to face operating system interview questions.

Many companies also conduct online written tests for the interview round where they ask questions in the form of Multiple Choice Questions (MCQs). So it also becomes very important for you to practice some operating system MCQs before you appear in these tests.

Top Operating System Interview Questions and Answers 2021

In this article, we have provided the frequently asked operating system interview questions. Please go through these, so you do not go offhanded for the interview.

Operating System Interview Questions Set-I [01 to 10]

Question: What is an operating system?
Answer: It is a program that provides an interface between the software and hardware of a computer. In other words, an OS offers an environment for the user to execute software using hardware.

Question: Name some functions of the operating system.

  • Memory management
  • Processor management
  • Device management
  • File management
  • Security
  • Job accounting
  • Control over system performance
  • Error detection
  • Communicate between user and software
  • Communication between software and hardware.

Question: Name the different operating systems.

  • Batched operating system.
  • Interactive operating system
  • Multi-processing operating system
  • Multitasking operating system
  • Distributed operating system
  • Multi-programmed operating system
  • Real-Time operating system
  • Timesharing operating system

Question: List the basic functions of OS file management.


  • Create and delete directories and files.
  • Use secondary storage for creating backup files.
  • Map file in secondary storage.
  • Give support to file modification.

Question: What is booting?

Answer: It is a procedure of turning on the computer by loading the kernel.

Question: What is the bootstrap program?
Answer: It is a program that resides in the kernel of an operating system, and when we boot the system, it is the first program that executes and stores the read-only memory (ROM).

Question: What is the use of an operating system?
Answer: An operating system acts as a management system between the system software and hardware, and guides hardware to act according to the provided software. It also controls the flow of the program and provides an environment so the software can communicate with system hardware.

Question: Define a multi-programming system.
Answer: In the multi-programming system, the system keeps different programs in different parts of the main memory simultaneously, and executes each of those concurrently.

Question: Define multitasking systems.
Answer: In a multitasking system, programs are kept in the main memory so the system can execute them simultaneously.

Question: What are the time-sharing systems?
Answer: In time-sharing systems, multiple users can use a specific program from different terminals at the same time.

Operating System Interview Questions Set-II [11 to 20]

Question: Give the advantages of a multiprocessor system.
Answer: Multi-processor, as the name suggests, uses more than one processor. With an increase in the processor count, the processing capability of the system increases too.

Question: What is virtual memory?
Answer: Virtual memory is a memory management method that helps to execute a process using primary and secondary memories. Though the program gets executed using the main memory, the resources and pages load from the secondary memory.

Question: What is a kernel in an operating system?
Answer: It is an essential part of the operating system, also known as the core of the OS. It is present in the main memory of the system and loads before any other part of the operating system. Every OS consists of a kernel. For example, the Linux kernel is one of the famous kernels, and Android also uses this kernel.

Question: What are the main functions of a kernel in an operating system?

  • Process management
  • Resource management
  • Disk management
  • Memory management
  • Device management
  • Facilitate communication between hardware and software.

Question: Define the 2 most popular types of kernels.

Answer: Though there are many types of kernels, only 2 of them are the most popular:

  1. Monolithic Kernel
  2. MicroKernel

Monolithic Kernel: In this type of OS kernel, all the user services and kernel services reside in the same memory space. Old operating systems would use this type of kernel. Some examples are Windows 95, 98, and Unix. Linux also uses it.

MicroKernel: This type of kernel is small in size, and all the user and kernel services reside in different memory addresses. Operating systems like macOS and Windows use microkernel.

Question: Give some disadvantages of Microkernel.

  • Complex process management.
  • Debugging the messaging is complex.
  • Loss in performance because of the requirement of more software.

Question: What is SMP?
Answer: It stands for Symmetric Multiprocessing (SMP), and it is an architecture that contains multiple processors to complete the process. All the processors share a single memory.

Question: What is asymmetric clustering?
Answer: Asymmetric clustering occurs when the server running the application finds some kind of cluster. In asymmetric clustering, one server tries to run the server application while others remain on standby mode.

Question: Explain a thread?
Answer: It is a flow of execution through the process code. A thread deals with the instruction to be executed.

Question: What is demanding paging?
Answer: Demanding pages is a concept used by the virtual machine. Only a part of the process needs to be present in the main memory to execute some process, which means that only a few pages will only be present in the main memory at any time, and the rest will be kept in the secondary memory.

Operating System Interview Questions Set-III [21 to 30]

Question: What is a process?
Answer: A program in execution is known as a process.

Question: Name all the states of a Process.

  • New
  • Running
  • Waiting
  • Ready
  • Terminate

Question: How is a thread different from a process?

  • The process is independent, whereas a thread is not.
  • A thread can assist other threads, whereas the process can not.
  • If one thread stops, the next thread starts executing, but this is not the case with a process.

Question: What is a deadlock?
Answer: When 2 processes are trying to execute simultaneously, and they are waiting for each other to finish the execution, as they are dependent on each other, this halt in execution is known as a deadlock. When the deadlock occurs in the program, the system usually freezes.

Question: What are the necessary conditions for a deadlock?

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

Question: What is starvation?

Answer: When a program is in process, and it does not get all the resources to execute, because other processes are using the same resources then this problem of not getting all needed resources is known as starvation.

Question: What is the difference between multitasking and multi-processing operating systems?


Multi-Tasking Multi-Processing
The operating system executes more than one task simultaneously using a single processor. The operating system executes more than one task using multiple processors.
Only one processor executes the tasks. More than one processor executes tasks.
It takes a moderate amount of time to execute all the tasks. It generally takes very little time to execute all tasks.
The processor shifts from one task to another, which makes it look like it is executing multiple tasks simultaneously, but, actually, here we only have one processor for task execution. Here, we have more than one processor. So multiple processes can be executed at the same time.

Question: Differentiate between paging and segmentation.


Paging Segmentation
Divides the virtual memory into physical memory. Divides the physical memory to the logical memory.
Paging divides the memory into fixed length. Segmentation divides the memory into arbitrary memory length.
Only loads information about the process. Loads the full logical portion of the page.
Pages are smaller than segments. Segments are generally larger.
It’s the hardware that divides the paging memory. The software divides the segmentation memory.

Question: What is a command interpreter?

Answer: It is a text field I/O interface between the user and the operating system. In the command interpreter, the user gives input through the keyboard using CLI commands. Command Prompt in Windows and Terminal in Linux and macOS are examples of the command interpreter.

Question: What is a daemon?
Answer: It stands for Disk and Execution monitor, and it is a long-running background process that acts on the request. The life cycle of the daemon commences with the system booting and continues until the system shuts down.

Operating System Interview Questions Set-IV [31 to 40]

Question: From where does the daemon originate and how we classify it?
Answer: The term daemon originated with UNIX. In UNIX, the daemon conventionally ends with ‘d’, for example ‘inetd’, ‘nfsd’, httpd’, and ‘lpd’.

Question: What is the race condition?
Answer: It is a situation that occurs when different operations are performed on the same data simultaneously, and the outcome of the execution depends on the order of the operations performed on the data. Evidently, the race condition can provide an undesirable outcome.

Question: What is process synchronization?
Answer: When the race condition occurs, it can lead to an undesirable outcome. So to prevent the race condition, we follow a process known as synchronization. Here, we ensure that only one process executes at a time.

Question: Explain PCB?

Answer: PCB stands for Process Control Block, and it an operating system data structure, which can collect and store information about the processes. It is also known as the process descriptor.

As soon as a process gets created, the OS creates a corresponding PCB to store the process status and information. With each transition, OS updates the PCB data structure.

Question: What is Semaphore?
Answer: It is a variable that is used to create a synchronized process. There are 2 types of semaphores:

  1. Counting semaphore.
  2. Binary semaphore.

Counting semaphore can have positive integer values, and Binary semaphore can only have 1 and 0 as variables.

Question: Explain FCFS and the main problem it causes.

Answer: It stands for First Come First Serve (FCFS), and it is a scheduling algorithm. According to this algorithm, the CPU serves that process first, which approaches it first. FCFS can cause the starvation problem in which the process does not get the proper resources.

Question: Name the different RAID levels.

  • 0 – Non-redundant striping
  • 1 – Mirrored Disks
  • 2 – Memory-style error-correcting codes
  • 3 – Bit-interleaved Parity
  • 4 – Block-interleaved Parity
  • 5 – Block-interleaved distributed Parity
  • 6 – P+Q Redundancy

Question: What is cache memory?
Answer: It is a volatile computer memory directly attached to the register, which provides high-speed data access to the processor.

Question: What is IPC?
Answer: IPC stands for Inter-Process Communication, and it is a mechanism, in which various processes can communicate with each other with the approval of the OS.

Question: Name the Various IPC mechanisms.

  • Sockets
  • Pipe
  • Shared Memory
  • Signals
  • Message Queues

Operating System Interview Questions Set-V [41 to 50]

Question: What is a context switch?
Answer: Context can be referred to as the data in the register. A context switch is a procedure in which the CPU changes from one task to another task.

Question: Give the difference between compiler and Interpreter.
Answer: A compiler first reads all the code at once and then tries to execute it, whereas an interpreter reads the code line by line and simultaneously executes it.

Question: What are sockets?

Answer: Sockets are the Inter-process Communication mechanisms that are used to provide point-to-point communication between 2 processes.

Sockets are often utilized in client-server applications because many protocols, such as FTP, SMTP, and POP3 use sockets to implement the connection between server and client.

Question: What do you understand by the main memory and secondary memory?

Answer: Main memory is directly connected to the computer processor, and it acts as a bridge between computer processors and secondary memory. The main objective of the main memory is to get the data from the secondary memory and feed it to the processor so that the appropriate actions could be performed.

RAM and ROM are the 2 main memories used by the system, whereas hard disk and other large-sized memories form the secondary memory.

As compared to the secondary memory, the main memory is straightforward and it is fast to access data from the main memory. That’s why processors directly communicate with the main memory.

Generally, the main memory does not store data permanently. Instead, it only holds data for a specific time and tries to give it to the processor for the further execution process.

Question: Can there be a deadlock situation with a single process?

Answer: No, to occur a deadlock situation, we need at least 2 dependent processes. A deadlock situation can only arise when these 4 conditions coincide:

  • Hold and Wait
  • No Preemption
  • Mutual Exclusion
  • Circular wait.

Question: What are interrupts?

Answer: These are the signals generated by the external input devices to stop the ongoing active process of the CPU. Interrupts use context switching so the CPU can switch between the current process and the new signal generated by the external device. Interrupts help in prioritizing the process execution of the CPU.

Question: What are zombie processes?

Answer: Formally, these processes are known as defunct processes. If a child process is still in the process table even after the parent process has been executed, this scenario could cause a zombie process.

Even the kill commands do not have any effect on these processes. If the Wait System Call read the exit status of the process, then the zombie process would remove from the process table.

Question: Explain pipe in OS?

Answer: Pipe is the method for exchanging information between processes. Generally, pipe forms a one-way communication, which means by using a pipe, a process can only send information, such as output or other parameters of the process to another process.

For setting a two-way communication between 2 processes, we require 2 pipes for both directions.

Question: What is the limitation of pipes for two-way communication between 2 processes?

Answer: If both the processes are the child process of the same parent, then only two-way pipe communication could be set between the processes.

Question: What do you know about the named pipe?

Answer: Generally, we use the un-named pipe to set communication between the related process, but if we want to communicate unrelated processes, then we need to use named pipes. Like a traditional unnamed pipe, named pipe is also a part of IPC (Interprocess Communication), and its life remains until the system is on.

Operating System Interview Questions Set-VI [51 to 60]

Question: Name the operations which are possible on a semaphore.

Answer: We can only perform 2 operations on a semaphore:

  1. Wait, and
  2. Signal.

Question: What do you know about mutex?

Answer: It is an abbreviation for Mutual Exclusion. It is a userspace program object that helps multiple threads to access the same resource, but not simultaneously. The sole purpose of a mutex is to lock a thread with a resource so the other threads can not use the same resource until the first thread finish executing.

Question: What is a critical section?

Answer: The program will behave oddly if program parts perform concurrent access to the shared resources. So to protect the shared resources of a program, we create a protected section, which is known as the critical section or critical region.

A critical section can only execute one process at a time, and this eliminates the problems that can be caused by concurrent accessing resources.

Question: What is process scheduling?

Answer: It is a routine followed by the process manager of the system. In this, the process manager can use different methods and strategies to remove a particular running process or select another process for the CPU.

Question: What is the difference between preemptive and non-preemptive scheduling?

Answer: Scheduling is divided into 2 categories; preemptive scheduling and non-preemptive scheduling.

Preemptive Scheduling Non-Preemptive Scheduling
Processes are allocated to the CPU for a limited period. A process remains in the CPU till it gets entirely executed.
If there is a new process that comes with high priority, then the ongoing CPU process has to stop. Here the priority of the process does not matter. The new process has to wait until the first process finishes execution.
There is a continuous switching between the running and ready states of the processes. This is not the case in non-preemptive scheduling.
Preemptive schedules the process on the basis of their priority. Non-preemptive uses the process burst time.
There is a high probability that the process with less priority will starve. Here process with less burst time will starve.

Question: Name the various scheduling algorithms.


  • First Come First Serve (FCFS).
  • Shortest Job First (SJF).
  • Priority Scheduling
  • Round Robin Scheduling

First Come First Serve: It follows the non-preemptive scheduling, and here the process requesting first gets the CPU.

Shortest Job First: It could be preemptive or non-preemptive. In this algorithm, that process gets the CPU that is closest to its execution. Here, CPU gives priority to those jobs which have a low execution time.

Priority Based Scheduling: It is also a preemptive algorithm, and here CPU is allocated to those processes first that have a high priority.

Round Robin Scheduling: It is a preemptive scheduling algorithm, and here each process gets equal time for execution.

Question: What are condition variables?

Answer: These are the synchronization objects, which can set some conditions for threads, and if the condition occurs then only the appropriate operations can be performed by the threads.

If the situation does not arise, then the threads have to wait for further execution. A condition variable is often used with critical sections and slim readers, where they help in binding and holding the threads.

Question: What is the reader-writer lock?

Answer: Reader-writer lock is used to prevent data integrity. This lock allows concurrent access to read operation, which means multiple threads can read data simultaneously.

But it does not allow concurrent write, and if one thread wants to modify data via writing, then all the other threads will be blocked from reading or writing data.

Question: What are the different types of memory used by the system?


  • Main memory, such as RAM and ROM.
  • Secondary memory, such as hard disk and e-drives.
  • Cache.
  • Internal process memory, such as registers.

Question: What is compaction?

Answer: The free memory of the system gets split into smaller pieces when a process loads or is removed from the memory. Compaction helps in accumulating these small loose pieces of memory into one substantial chunk so that more memory can be allocated to other processes.

Operating System Interview Questions Set-VII [61 to 70]

Question: What is a page in OS?

Answer: A page can be defined as the smallest unit of data, and it is a fixed-length contiguous block of virtual memory.

Question: Explain page frames.

Answer: When a page is transferred from the secondary memory to the main memory, then it requires a fixed length of a continuous physical memory block, known as a page frame. It is the job of the operating system to map the pages in the page frames.

Question: What is the difference between logical and physical addresses?


Logical Address Physical Address
The CPU generates it. It is the real address of the program in the memory.
A user can access the logical address of the program. The physical address can be accessed directly.
CPU generates a logical address at the execution time. It is generated by the Memory Management Unit(MMU) at the creation time.

Question: What is the page fault?

Answer: It is an error that occurs when the CPU tries to access a specific block of memory address that is not present in the physical memory (RAM).

Question: What is thrashing?

Answer: It is a scenario when continuous page fault and paging activities occur. Thrashing could lead to a program collapse and degraded CPU performance.

Question: What do you know about the library?

Answer: A library is a collection of files that contains subroutines, data, and other objects that can be used by other programs.

Question: What is the difference between a program and a process?


Program Process
It is a set of instructions that are written in a specific programming language. It is an instance of a program that is about to be executed by one or many threads.
A program is static in nature that is present in the file. Processes are dynamic and generated during execution time.
Programs are generally stored in secondary memory, which makes them portable. Processes are not portable and they reside in the main memory.
The program can live in the main memory for eternity. A process time period is limited and it either executes or fails.
Programs are passives entities. Processes are active entities.

Question: What are APIs?

Answer: API stands for Application Program Interface, and it is a collection of libraries and subprograms. APIs are used to set communication between 2 programs i.e. API provides a general way of sending and receiving data between applications.

Question: What is Belady’s anomaly?

Answer: It is a situation that occurs in the OS when there is an increase in page faults by the CPU because additional memory has been introduced to the system, which results in increasing page frames.

Question: What do you know about cascading termination?

Answer: When a process finishes execution, then the OS terminates the process via the exit system call. Only the parent process can cause the termination of its child processes, so when the parent process gets entirely executed and terminated, then its child process also gets terminated automatically.

This phenomenon of a process triggering termination of another process is known as cascading termination.


With this, we have reached the end of our operating system interview questions and answers. An operating system is the core program for any computer. Without it, a system is just a piece of hardware.

A user will not be able to communicate or interact with the system if there is no operating system. Although all the operating system interview questions we have provided here are the important ones, there is no guarantee that the interviewer will be asking you the exact same questions as detailed above.

The only purpose of these OS interview questions is to give you an idea of what type of interview questions you can expect during the interview.

If you have an IT job interview in 2021, we suggest you read these operating system interview questions and answers to refresh your knowledge about the operating system and its working.

It does not matter if you are going for a developer job interview or some other technical support interview, you are still supposed to have explicit knowledge of the OS.

If you had appeared in an interview for the last 5 to 6 months where you have been asked any question related to the OS please share the same via comments. We would update our list of the best operating system interview questions with those.

If you like this article or have any suggestions, please leave them in the comments section below.

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