Operating Systems Interview Questions and Answers for 2025 – Beginner to Advanced | JaganInfo

An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs.

Managing hardware resources, providing user interface, managing files and directories, process management, memory management, device management, and security.

A process is an instance of a program in execution, containing the program code and its current activity, including program counter and registers.

New, Ready, Running, Waiting (Blocked), and Terminated.

Multitasking is the ability of an OS to execute multiple tasks or processes concurrently by rapidly switching between them.

A thread is the smallest unit of execution within a process. A process may contain multiple threads sharing resources but executing independently.

Context switching is the process by which the CPU switches from one process or thread to another, saving the state of the current task and loading the state of the next.

Deadlock is a situation where two or more processes are waiting indefinitely for resources held by each other, causing a standstill.

Virtual memory is a memory management technique where the OS uses hardware and software to allow a computer to compensate for physical memory shortages by temporarily transferring data to disk storage.

A file system manages how data is stored and retrieved on storage devices; it organizes files and directories and controls access.

The process table is a data structure maintained by the OS to keep track of all processes, including process state, process ID, program counter, registers, and memory limits.

Process scheduling is the method by which the OS decides which process gets to use the CPU and for how long, using scheduling algorithms like Round Robin, FCFS, Priority Scheduling, etc.

A semaphore is a synchronization primitive used to control access to shared resources and prevent race conditions.

The critical section is a part of a program where shared resources are accessed, requiring mutual exclusion to prevent conflicts.

Paging divides memory into fixed-size pages, providing non-contiguous memory allocation. Segmentation divides memory into variable-sized segments based on logical divisions.

Thrashing occurs when excessive paging operations slow down system performance, usually due to insufficient memory.

Demand paging loads pages into memory only when they are needed, not in advance, to optimize memory usage.

Preemptive scheduling allows the OS to suspend a running process to start another; non-preemptive lets the process run until completion or blocking.

System calls provide an interface for user programs to request services from the OS kernel, like file management and process control.

Mutual exclusion ensures that only one process accesses a critical resource at a time, preventing data inconsistency.

The scheduler selects and allocates CPU time to processes, optimizing resource utilization and system responsiveness.

IPC allows processes to share data and synchronize actions using mechanisms such as pipes, message queues, shared memory, and sockets.

A race condition occurs when two or more processes access shared data concurrently, and the final result depends on the sequence of access.

The kernel is the core part of an OS responsible for managing system resources and allowing communication between hardware and software.

File permissions control the access levels (read, write, execute) for users and groups to files and directories.

Algorithms that check the system for deadlock conditions by analyzing resource allocation and process states.

Policies like FIFO, LRU, and Optimal determine which pages to swap out when memory is full.

Time-sharing enables multiple users to interact with a computer at the same time by quickly switching between tasks.

An RTOS guarantees timely and deterministic response to external events, used in embedded systems and critical applications.

A memory management scheme that eliminates the need for contiguous allocation by dividing memory into fixed-sized pages.

A deadlock avoidance algorithm that checks resource allocation states to ensure safe operation before granting requests.

Algorithms determine the order in which processes are given CPU time, such as Round Robin, Priority, Shortest Job First, and Multilevel Queue.

Semaphores are synchronization tools; binary semaphores (mutex) for mutual exclusion and counting semaphores for resource management.

Processes are independent execution units with separate memory space; threads are lightweight and share the same memory within a process.

Pages are loaded into memory only when required, reducing memory usage and improving efficiency.

Inode stores metadata about a file, such as owner, permissions, timestamps, and pointers to data blocks.

An error caused by accessing memory that the program is not allowed to, often due to invalid pointers or buffer overflows.

Only required segments of a program are loaded into memory on demand, improving utilization and enabling larger programs.

Batch, Time-sharing, Distributed, Real-time, Network, and Mobile Operating Systems with distinct characteristics.

An event that occurs when a program tries to access a page not currently in physical memory, triggering a page load.

Thrashing is excessive paging leading to performance degradation; prevented by working set management and load control.

User mode restricts code access to hardware and memory; kernel mode has full access for OS functions and device management.

Race conditions occur due to unsynchronized access to shared data; avoided by using locks, semaphores, and atomic operations.

An abstraction layer on top of file systems providing a uniform interface to different file system types.

A terminated process that still has an entry in the process table, waiting for the parent process to read its exit status.

Fork creates a new process by duplicating an existing one; exec replaces the process’ memory with a new program.

Both are synchronization tools; mutex allows exclusive access to a resource, semaphore manages access by multiple processes using counts.

LRU (Least Recently Used) replaces the page which hasn’t been used for the longest time to manage memory efficiently.

Monolithic kernels offer performance and simplicity but less stability; microkernels promote modularity and fault isolation but with overhead.

Kernel preemption allows the OS to suspend kernel tasks to schedule higher priority processes, improving real-time responsiveness.