Explain the difference between Kernel Mode and User Mode. Why is this dual-mode operation necessary for system security?
Junior
What is the primary purpose of an Operating System, and what are its core functions?
Junior
What are privileged instructions, and why can they only run in kernel mode?
Junior
What are the different types of operating systems (batch, time-sharing, real-time, distributed, embedded)?
Junior
What is multiprogramming, and how does it improve CPU utilization?
Junior
Explain the difference between Type 1 (Bare Metal) and Type 2 (Hosted) Hypervisors.
Mid
Explain the Bootstrapping process. What is the role of the BIOS/UEFI and the bootloader in handing control to the OS?
Mid
What is the difference between symmetric multiprocessing (SMP) and asymmetric multiprocessing?
Mid
What is the difference between protection and security in an operating system?
Mid
Compare Monolithic Kernels and Microkernels. What are the tradeoffs regarding performance, modularity, and system stability?
Senior
What is the conceptual difference between a Virtual Machine and a Container, focusing on the OS mechanisms like Namespaces and Cgroups that enable containerization?
Senior
How do OS-level Namespaces and Cgroups enable the isolation required for containers?
Senior
Explain the difference between a Type-1 and Type-2 hypervisor. How do containers using namespaces/cgroups differ conceptually from Virtual Machines?
Senior
Compare layered, modular, and hybrid kernel architectures.
Senior
Processes & Threads
Describe the Process State Transition Diagram. What triggers a process to move from Running to Waiting vs. Ready?
Junior
Explain the fundamental differences between a process and a thread. How do they differ in terms of memory sharing and overhead?
Junior
What is a Process Control Block (PCB), and what specific information does the OS store in it to manage a process?
Junior
What resources are shared between threads of the same process, and what are kept private?
Junior
Explain the difference between a Program, a Process, and a Thread.
Junior
What are the benefits and costs of multithreading an application?
Junior
What is a zombie process, and how does it differ from an orphan process? Why is it important for a parent to 'wait' on its child?
Mid
Explain the 'copy-on-write' mechanism used during a fork() system call. Why is it efficient?
Mid
What is the difference between a user-level thread and a kernel-level thread, and what are the tradeoffs of each model?
Mid
Explain the fork() and exec() model of process creation. What happens to the address space during a fork()?
Mid
Why is context switching between threads generally faster than between processes?
Mid
When would you choose a multithreaded architecture over a multiprocess one for a single-machine application?
Mid
What is a Thread Control Block (TCB), and how does it differ from a PCB?
Mid
How do the many-to-one, one-to-one, and many-to-many multithreading models differ?
Mid
System Calls Interrupts & Kernel Interaction
What is a system call, and how does it differ from a standard library function call?
Junior
What is the difference between an Interrupt and a Trap (or Exception)? Give an example of when each would occur.
Mid
What is the role of the Interrupt Vector Table in handling hardware signals?
Mid
Explain the difference between Polling, Interrupt-driven I/O, and Direct Memory Access (DMA).
Mid
What exactly happens during a System Call? Walk through the transition from user space to kernel space.
Senior
Cpu Scheduling
Explain the difference between preemptive and non-preemptive scheduling. When would you prefer one over the other?
Junior
What is the difference between Throughput, Turnaround Time, and Response Time?
Junior
How does a round robin scheduler handle a process that requires more time than the allocated time quantum?
Junior
How does priority scheduling work, and how are priorities assigned to processes?
Junior
What is a Context Switch? Describe the steps the OS takes during a switch and explain why it is considered overhead.
Mid
What is Starvation in the context of priority scheduling, and how does Aging solve it?
Mid
What is the convoy effect in FCFS scheduling, and how do algorithms like Round Robin mitigate it?
Mid
How does a Multi-level Feedback Queue work to balance the needs of I/O-bound and CPU-bound processes?
Mid
What are the primary goals of a CPU scheduler? Explain the tradeoffs between throughput, turnaround time, and response time.
Mid
How does the Round Robin algorithm work, and how does the choice of time quantum size affect response time vs. throughput?
Mid
Explain the difference between a short-term, medium-term, and long-term scheduler.
Mid
Compare and contrast Round Robin and Shortest Job First scheduling. In what scenario would Round Robin be preferred?
Mid
What is swapping, and how does the medium-term scheduler use it to manage memory?
Mid
What is the role of the Dispatcher, and what is meant by dispatch latency?
Mid
Explain the difference between Shortest Job First (SJF) and Shortest Remaining Time First (SRTF) scheduling.
Mid
How does Multilevel Queue scheduling work, and how does it differ from Multilevel Feedback Queue?
Mid
Process Synchronization
What is a Race Condition? Provide a conceptual example of how it can lead to data inconsistency.
Junior
What is the conceptual difference between a mutex and a semaphore? When would you use a counting semaphore instead of a binary one?
Mid
Explain the critical section problem and the three requirements for a valid solution.
Mid
What is the difference between a spinlock and a blocking lock? When would you prefer one over the other?
Mid
Describe the Producer-Consumer (Bounded Buffer) problem and how semaphores are used to solve it.
Mid
How do the wait() and signal() operations of a semaphore work internally, and why must they be atomic?
Mid
What is a monitor, and how do condition variables with wait() and signal() differ from semaphores?
Mid
Explain Peterson's solution to the critical-section problem. What assumptions does it rely on?
Mid
How do hardware instructions like Test-and-Set and Compare-and-Swap help implement synchronization primitives?
Mid
Describe the Dining Philosophers problem. What solutions prevent deadlock in it?
Mid
What is Priority Inversion, and how does Priority Inheritance mitigate it?
Senior
Explain the readers-writers problem and the trade-offs between reader-preference and writer-preference solutions.
Senior
Deadlocks
What are the four Coffman Conditions necessary for a deadlock to occur?
Junior
Compare Deadlock, Livelock, and Starvation.
Mid
What is a Resource Allocation Graph, and how can it be used to detect a deadlock?
Mid
What is the Ostrich approach to handling deadlocks, and why do general-purpose OSs often use it?
Mid
Explain the difference between Deadlock Prevention and Deadlock Avoidance. How does the Banker's Algorithm ensure a Safe State?
Senior
How does the Banker's Algorithm determine if a system is in a Safe State?
Senior
How does deadlock detection and recovery work when the OS allows deadlocks to occur?
Senior
Memory Management & Virtual Memory
What is Virtual Memory, and how does it allow a program to run even if it is larger than the available physical RAM?
Junior
What is Virtual Memory, and what are the primary benefits it provides to a programmer?
Junior
What is the Translation Lookaside Buffer (TLB), and how does it speed up address translation?
Mid
What is 'thrashing' in an OS? What are the primary causes, and how can the OS detect or prevent it?
Mid
Explain the difference between Internal and External Fragmentation. Which occurs in Paging and which in Contiguous Allocation?
Mid
Compare paging and segmentation. What are the advantages of a segmented paging approach?
Mid
What is a Page Fault? Walk through the steps the OS takes to resolve one.
Mid
Explain the difference between Logical (Virtual) and Physical addresses. What is the role of the MMU?
Mid
What is Paging, and how does it solve the problem of External Fragmentation?
Mid
Compare the FIFO, LRU, and Optimal page-replacement algorithms. Why is Optimal impossible to implement in practice?
Mid
What is the difference between compile-time, load-time, and execution-time address binding?
Mid
What is memory compaction, and what problem does it solve in contiguous allocation?
Mid
What are memory-mapped files, and what advantages do they offer over regular read/write I/O?
Mid
How does the Clock (Second-Chance) page-replacement algorithm approximate LRU?
Mid
Explain Belady's Anomaly. Why does it occur in FIFO page replacement but not in LRU?
Senior
Compare the LRU and FIFO page replacement algorithms, and what is Belady's Anomaly?
Senior
What is a Page Table, and why do modern systems use Multi-level Page Tables instead of a single flat table?
Senior
Explain the Working Set Model. How is the working set window used to estimate the degree of multiprogramming?
Senior
What is an inverted page table, and what problem does it solve compared to a per-process page table?
Senior
How do you compute the Effective Access Time in a paged system with a TLB?
Senior
How do LFU and MFU page-replacement algorithms work, and what are their drawbacks?
Senior
What is the Page-Fault Frequency (PFF) scheme for controlling thrashing?
Senior
How does the OS decide how many frames to allocate to each process (global vs local allocation)?
Senior
File Systems
Compare the different directory structures (single-level, two-level, tree, acyclic-graph).
Junior
What are the different file access methods (sequential, direct, indexed)?
Junior
What is an 'inode' in a Unix-like file system? What kind of information does it store and what does it not store?
Mid
Explain the difference between a hard link and a symbolic (soft) link. What happens to the file if the original link is deleted in each case?
Mid
What is a File Descriptor, and how does the OS use the Open-File Table to manage file access across processes?
Mid
How does free-space management work using a bit vector versus a linked list?
Mid
What is the FAT (File Allocation Table), and how does it track file blocks?
Mid
What does it mean to mount a file system, and what does the OS do during mounting?
Mid
What is the purpose of Journaling in a file system, and how does it help with recovery after a system crash?
Senior
Compare contiguous, linked, and indexed file allocation methods. Which one is most efficient for random access?
Senior
Explain the concept of a Virtual File System (VFS) layer.
Senior
Inter Process Communication
What is a Pipe, and what is the difference between a Named and Unnamed pipe?
Junior
Explain how pipes work for communication between a parent and child process.
Junior
What are the primary mechanisms for Inter-Process Communication? Compare Shared Memory vs. Message Passing in terms of speed and ease of implementation.
Mid
What are signals in a Unix-like OS, and how are they used for inter-process communication?
Mid
How do sockets function as an IPC mechanism at the OS level?
Mid
I O Systems
What is a device driver, and what role does it play in the OS I/O subsystem?
Junior
Explain the difference between Polling and Interrupt-driven I/O. In what scenario would Polling actually be more efficient?
Mid
What is DMA, and why is it critical for high-speed data transfer between devices and memory?
Mid
Explain the difference between blocking, non-blocking, and asynchronous I/O.
Mid
Compare Buffering and Spooling. Give a real-world example of each.
Mid
What is the role of buffering and caching in the I/O subsystem?
Mid
Storage & Disk Management
Explain Disk Scheduling algorithms like SCAN and C-LOOK. How do they reduce seek time compared to FCFS?
Mid
What are RAID levels, and how do RAID 0, 1, and 5 differ in terms of performance and redundancy?
Mid
What are the key differences between an SSD and an HDD from the OS's storage-management perspective?
Mid
How does the SSTF disk-scheduling algorithm work, and what problem (starvation) can it cause?
Mid
What is the difference between SCAN, C-SCAN, LOOK, and C-LOOK disk-scheduling algorithms?
Mid
What is the OS page cache (buffer cache), and how does it improve file I/O performance?
Mid
Protection & Real Time Systems
What is the principle of least privilege, and how does the OS enforce it using Access Control Lists or capabilities?
Mid
What defines a 'Real-Time Operating System' (RTOS)? What is the difference between 'hard' and 'soft' real-time constraints?
Mid
What is a Real-Time Operating System (RTOS), and how does its scheduler differ from a standard OS?
Senior
Explain the Access Matrix model of protection. How do ACLs and Capability Lists represent different views of this matrix?
Senior
Top 123 Operating Systems Interview Questions And Answers 2025 | TechPrep