OS Interview Questions and Answers for 5 years experience

1. What is an operating system?

   • Answer: An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs. It acts as an intermediary between the user and the hardware, allowing users to interact with the computer and run applications without needing to understand the low-level details of the hardware.

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

   • Answer: A process is an independent, self-contained execution environment with its own memory space, resources, and security context. A thread, on the other hand, is a lightweight unit of execution within a process. Multiple threads can share the same memory space and resources of a process, allowing for concurrent execution within a single process. Processes are heavier to create and manage than threads.

3. Describe the different states a process can be in.

   • Answer: A process typically goes through several states: New (created but not yet running), Ready (waiting for CPU time), Running (currently executing instructions), Blocked/Waiting (waiting for an event like I/O), and Terminated (completed execution).

4. What is context switching?

   • Answer: Context switching is the process of saving the state of a currently running process and loading the state of another process so that the CPU can switch between them. This allows the OS to give the illusion of multiple processes running concurrently.

5. Explain different types of scheduling algorithms.

   • Answer: Examples include First-Come, First-Served (FCFS), Shortest Job First (SJF), Priority Scheduling, Round Robin, and Multilevel Queue Scheduling. Each has its advantages and disadvantages in terms of fairness, response time, and throughput.

6. What is deadlock? Explain how to prevent it.

   • Answer: Deadlock occurs when two or more processes are blocked indefinitely, waiting for each other to release resources that they need. Prevention techniques include mutual exclusion (only one process can access a resource at a time), hold and wait (prevent processes from holding resources while waiting for others), no preemption (resources cannot be forcibly taken away from a process), and circular wait (prevent circular dependencies in resource allocation).

7. What is paging and its advantages?

   • Answer: Paging is a memory management scheme that divides both physical and logical memory into fixed-size blocks called pages and frames, respectively. Advantages include efficient memory utilization, support for virtual memory, and easier memory allocation and deallocation.

8. What is segmentation? How does it differ from paging?

   • Answer: Segmentation divides logical memory into variable-sized blocks called segments, each representing a logical unit (like a program or data structure). Unlike paging, which uses fixed-size blocks, segmentation allows for variable-sized blocks. Segmentation offers better support for modular programming, but can lead to external fragmentation.

9. Explain virtual memory.

   • Answer: Virtual memory allows processes to access more memory than is physically available. It uses paging or segmentation to map logical addresses to physical addresses, allowing parts of a program to reside on secondary storage (like a hard drive) and be loaded into main memory only when needed.

10. What is a page fault?

    • Answer: A page fault occurs when a process tries to access a page that is not currently in main memory. The OS then needs to load the page from secondary storage into main memory before the process can continue.

11. What is the role of a file system?

    • Answer: A file system organizes and manages files and directories on a storage device, allowing users to easily store, retrieve, and manipulate data. It handles file creation, deletion, access control, and storage allocation.

12. Explain different file system types (e.g., FAT, NTFS, ext4).

    • Answer: FAT (File Allocation Table) is an older file system, simple and widely compatible. NTFS (New Technology File System) is used in Windows, offering features like security and journaling. ext4 is a common Linux file system, known for its performance and reliability. Each has different strengths and weaknesses regarding features, performance, and scalability.

13. What is I/O management?

    • Answer: I/O management is the OS function responsible for managing input/output operations between the computer and its peripherals (e.g., keyboard, mouse, disk drives). It handles device drivers, interrupts, and data transfer.

14. What is a device driver?

    • Answer: A device driver is a software program that allows the OS to communicate with a specific hardware device. It translates OS commands into instructions understood by the hardware.

15. Explain different types of memory (RAM, ROM, Cache).

    • Answer: RAM (Random Access Memory) is volatile memory used for storing currently running programs and data. ROM (Read-Only Memory) stores permanent instructions and data, even when the power is off. Cache memory is a small, fast memory that stores frequently accessed data for quicker access.

16. What is the difference between kernel and user space?

    • Answer: The kernel is the core of the OS, running in kernel space with privileged access to all hardware and system resources. User space is where user applications run, with limited access to system resources for security.

17. What is an interrupt? How does it work?

    • Answer: An interrupt is a signal that tells the CPU to stop its current task and execute a special routine (interrupt handler) to handle an event, such as a device needing attention or an error condition.

18. Explain the concept of a system call.

    • Answer: A system call is a request made by a program to the OS kernel to perform a privileged operation, such as reading a file or creating a process. It's the mechanism for user-space programs to interact with the kernel.

19. What are semaphores and mutexes?

    • Answer: Semaphores are integer variables used for process synchronization. Mutexes (mutual exclusion) are a special type of semaphore that ensures only one process can access a critical section at a time.

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