OSInterview Questions

Difference Between Process and Thread

A process is an independent program in execution with its own private memory space, while a thread is a lighter unit of execution that lives inside a process a…

What is a Deadlock?

A deadlock is a situation where a set of processes are permanently blocked because each holds a resource the others need and is waiting for a resource another…

Difference Between Paging and Segmentation

Paging divides memory into fixed-size blocks called pages (mapped to equal-size frames in physical memory), while segmentation divides memory into variable-siz…

What is a Semaphore?

A semaphore is a synchronization primitive — an integer counter with atomic wait (P/down) and signal (V/up) operations — used to control access to shared resou…

What is a Context Switch?

A context switch is the process of saving the CPU state of a currently running task and loading the saved state of another task, so a single CPU core can appea…

What is Virtual Memory?

Virtual memory is a technique that gives each process the illusion of a large, private, contiguous address space by mapping virtual addresses to physical RAM (…

Difference Between Mutex and Semaphore

A mutex is a locking primitive owned by exactly the thread that acquires it and enforces mutual exclusion over a single resource, while a semaphore is a counte…

What is CPU Scheduling?

CPU scheduling is the OS mechanism that decides which ready process or thread gets to run on the CPU next, aiming to balance throughput, fairness, and responsi…

What is Thrashing in Operating Systems?

Thrashing is a state where a system spends most of its time swapping pages between RAM and disk rather than executing actual instructions, causing CPU utilizat…

What is a Page Fault?

A page fault is a hardware trap raised by the MMU when a running program accesses a virtual memory page that is not currently mapped to a physical frame, forci…

Preemptive vs Non-Preemptive Scheduling

Preemptive scheduling lets the OS forcibly suspend a running process to give the CPU to another, while non-preemptive scheduling requires the running process t…

What is a Race Condition?

A race condition occurs when two or more threads or processes access shared data concurrently and the final outcome depends on the unpredictable timing of thei…

What is the Critical Section Problem?

The critical section problem is the challenge of designing a protocol that lets multiple concurrent processes or threads take turns using a shared resource saf…

What is a System Call?

A system call is the controlled interface a user-space program uses to request a privileged service from the operating system kernel, such as reading a file, a…

What is Demand Paging?

Demand paging is a virtual memory technique where a page is loaded into physical memory only when a process actually references it, rather than loading the who…

What is a Zombie Process?

A zombie process is a process that has finished execution but still has an entry in the process table because its parent has not yet read its exit status.

What is Inter-Process Communication (IPC)?

Inter-process communication (IPC) is the set of mechanisms an operating system provides for separate processes — each with its own isolated address space — to…

What is the Producer-Consumer Problem?

The producer-consumer problem is a classic synchronization challenge where one or more producer threads generate data into a shared, fixed-size buffer while on…

What is an Interrupt?

An interrupt is a signal to the CPU, generated by hardware or software, that forces the processor to pause its current instruction stream and immediately trans…

What is First-Come-First-Served (FCFS) Scheduling?

First-Come-First-Served (FCFS) is a non-preemptive CPU scheduling algorithm that runs processes strictly in the order they arrive in the ready queue, giving ea…

What is Shortest-Job-First (SJF) Scheduling?

Shortest-Job-First (SJF) is a scheduling algorithm that always dispatches the ready process with the smallest total CPU burst time next, which provably minimiz…

What is Shortest-Remaining-Time-First (SRTF) Scheduling?

Shortest-Remaining-Time-First (SRTF) is the preemptive version of Shortest-Job-First: whenever a new process arrives, the scheduler compares its burst time to…

What is Priority Scheduling?

Priority scheduling dispatches the ready process with the highest priority value next, rather than by arrival order or burst time, and can be implemented as ei…

What is Multilevel Queue Scheduling?

Multilevel queue scheduling partitions the ready queue into several separate queues by process type — such as system, interactive, and batch — each with its ow…