Top Operating System Interview Question Answers

  Here are some common operating system interview questions along with their answers:

What is an Operating System?

• Answer: An operating system (OS) is a software that manages computer hardware and provides services for computer programs. It acts as an intermediary between the hardware and the user applications.

What are the functions of an Operating System?

• Answer: The functions of an operating system include process management, memory management, file system management, device management, security, and user interface.

What is the difference between a process and a thread?

• Answer: A process is an instance of a program in execution, while a thread is a lightweight process within a process. Threads share the same memory space, while processes have their own memory space.

What is virtual memory?

• Answer: Virtual memory is a memory management technique that provides an illusion to the user of a contiguous memory space larger than the physical memory (RAM) available in the system. It allows running programs to use more memory than is physically available by using disk space as an extension of RAM.

Explain the difference between multiprogramming, multitasking, multiprocessing, and multithreading.

• Multiprogramming: Running multiple programs concurrently by the operating system.

• Multitasking: Switching between different tasks or programs rapidly to give the appearance of simultaneous execution.

• Multiprocessing: Utilizing multiple processors or CPU cores to execute multiple processes concurrently.

• Multithreading: Executing multiple threads within a single process, allowing for concurrent execution of tasks.

What is a deadlock? How can it be avoided?

• Answer: A deadlock is a situation in which two or more processes are unable to proceed because each is waiting for the other to release a resource. Deadlocks can be avoided by employing techniques such as deadlock prevention, deadlock avoidance, and deadlock detection along with appropriate strategies like resource allocation graphs and deadlock recovery.

Explain the concept of a file system.

• Answer: A file system is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. It manages how data is stored, retrieved, and updated on storage devices such as hard drives and SSDs.

What is a kernel in an operating system?

• Answer: The kernel is the core component of an operating system that provides essential services and functions, such as process management, memory management, device management, and system calls. It directly interacts with the hardware and manages system resources.

What is a shell?

• Answer: A shell is a user interface for accessing the services of an operating system. It allows users to interact with the operating system by accepting commands and executing them. Examples include Bash, PowerShell, and Command Prompt.

What is a process control block (PCB)?

• Answer: A process control block (PCB) is a data structure used by the operating system to store information about a process, such as its process ID, state, priority, CPU registers, and memory management information. It is used for process management and scheduling.

What is a semaphore?

• Answer: A semaphore is a synchronization construct used in operating systems to control access to shared resources by multiple processes or threads. It is typically implemented as a non-negative integer variable and supports two primary operations: wait (P) and signal (V).

Explain the difference between a mutex and a semaphore.

• Answer: A mutex is a synchronization primitive that allows only one thread to access a resource at a time. It provides exclusive access to the resource. In contrast, a semaphore is a generalized synchronization primitive that can be used to control access to multiple instances of a resource. Semaphores can allow multiple threads to access a resource simultaneously up to a certain limit.

What is a page fault?

• Answer: A page fault occurs when a program accesses a memory page that is not currently located in physical memory (RAM) and needs to be retrieved from secondary storage (usually the disk). This retrieval process is managed by the operating system's memory management unit.

11. What is a context switch?

    • Answer: A context switch is the process of saving and restoring the state of a CPU so that multiple processes can share the CPU. It involves storing the current state of the running process, loading the state of a different process, and then resuming execution from where it left off for the new process.

Explain the difference between internal fragmentation and external fragmentation.

• Answer:
  • Internal fragmentation: Occurs when memory allocated to a process is larger than the requested memory, leading to wasted space within a memory block.
  • External fragmentation: Occurs when there is enough total memory space to satisfy a request, but it is not contiguous, leading to inefficient memory utilization.

What is a file descriptor?

• Answer: A file descriptor is an abstract indicator used to access a file or other input/output resource in Unix-like operating systems. It is typically represented by a non-negative integer, which serves as an index into the file descriptor table maintained by the operating system.

What is a zombie process?

• Answer: A zombie process is a process that has completed execution but still has an entry in the process table. It is in a "defunct" state, meaning that it is waiting for its parent process to retrieve its exit status. Zombie processes consume system resources but do not execute any code.

What is the role of the init process in Unix-like operating systems?

• Answer: The init process is the first process started by the kernel during the boot process and serves as the ancestor of all other processes. Its primary role is to initialize the system and start other essential processes and daemons.

What is the difference between a fork() system call and exec() system call?

• Answer: The fork() system call is used to create a new process, which is an exact copy of the calling process. The exec() system call is used to replace the current process's memory space with a new program, typically used after a fork() to execute a different program in the child process.

Explain the concept of a file descriptor table.

• Answer: A file descriptor table is a data structure maintained by the operating system for each process to keep track of the files and other I/O resources opened by the process. It maps file descriptors to file objects and maintains information such as file offset and access mode.