Operating System Viva questions top 10/ interview questions

1. What is an Operating System?

An Operating System (OS) is system software that acts as a bridge between users and computer hardware. It manages hardware resources and provides services to application software. An OS handles tasks like memory management, process scheduling, and device control. It ensures that programs and users can run smoothly without interfering with each other. Examples include Windows, Linux, macOS, and Android. The OS also provides a user interface, either graphical (GUI) or command-line (CLI). Without an OS, a computer would be unusable. It organizes files, maintains security, and manages system performance. In short, the OS is the heart of any computing device.

2. What are the main functions of an Operating System?

The primary functions of an Operating System are process management, memory management, file system management, and device management. It ensures efficient execution of processes by scheduling CPU time. Memory management keeps track of each byte in a computer’s memory and allocates memory spaces. File system management organizes, stores, retrieves, and protects data on storage devices. Device management handles communication with input/output devices via drivers. It also manages security and access controls. The OS offers a user interface to interact with the system. It also handles error detection and system performance monitoring. Overall, it makes system resources accessible and optimized.

3. What is a process in an Operating System?

A process is an instance of a program in execution. It includes the program code, its current activity, and a set of resources like CPU registers, memory, files, and I/O devices. Processes are fundamental units that the OS manages for multitasking. Each process has a unique Process ID (PID) and moves through different states like ready, running, waiting, and terminated. The OS allocates resources to processes and ensures smooth scheduling. Processes may be independent or dependent on other processes. Multitasking OSes manage multiple processes simultaneously. Process control blocks (PCBs) store all information about a process. Processes help achieve better CPU utilization.

4. What is the difference between a process and a thread?

A process is a complete program in execution, while a thread is the smallest unit of execution within a process. Threads share the same memory and resources of their parent process but execute independently. Processes are isolated from each other and require more overhead to create. In contrast, threads are lighter and easier to create and terminate. Communication between threads (in the same process) is simpler than inter-process communication (IPC). Threads are commonly used for parallelism to perform multiple tasks concurrently. Multithreading improves application responsiveness. Each process has its own memory space, but threads within a process share memory. Both enhance multitasking but operate at different levels.

5. What is deadlock in Operating Systems?

Deadlock is a situation in Operating Systems where a set of processes get stuck indefinitely because each process is waiting for a resource held by another. It commonly occurs in multi-processing systems where resources are shared. For deadlock to occur, four conditions must be true simultaneously: mutual exclusion, hold and wait, no preemption, and circular wait. Deadlocks cause system performance issues and can freeze applications. Operating Systems use various strategies to handle deadlocks, such as prevention, avoidance, detection, and recovery. For example, Banker's Algorithm helps avoid deadlocks. Resource allocation graphs can detect potential deadlocks. Solving deadlocks is critical for system stability and reliability.

6. What is virtual memory?

Virtual memory is a memory management technique that gives an application the illusion it has a contiguous block of memory, even if physically it is fragmented or exceeds actual RAM. It uses hardware and software to map memory addresses. Virtual memory uses disk storage (like a hard drive) as an extension of RAM by swapping data back and forth using a technique called paging. This allows more programs to run simultaneously and enables larger programs to run even on small physical memory. It improves multitasking and system stability. However, excessive use of virtual memory can lead to slowdowns, known as thrashing. Operating Systems manage virtual memory efficiently for performance.

7. What is paging in an Operating System?

Paging is a memory management scheme where physical memory is divided into fixed-sized blocks called frames, and logical memory is divided into pages. When a process needs memory, its pages are loaded into any available memory frames. Paging avoids external fragmentation and allows non-contiguous memory allocation. The OS maintains a page table that maps logical addresses to physical addresses. When a page is not in memory, a page fault occurs, and the OS must fetch it from disk. Paging is fundamental to implementing virtual memory. It increases system efficiency and flexibility. Modern OSes like Windows and Linux use paging extensively to manage memory smartly.

8. Explain the concept of context switching.

Context switching is the process of saving the state (context) of a currently running process and loading the state of the next scheduled process. It enables multitasking, allowing multiple processes to share a single CPU efficiently. The saved context includes information like CPU registers, program counter, and memory management data. When the OS decides to switch tasks (based on scheduling policies), it stores the old process's context and loads the new one. Context switching adds overhead to the CPU, as it consumes time and system resources. However, it is crucial for responsiveness and effective process management. Optimized context switching improves system performance and user experience.

9. What are the different types of schedulers in an Operating System?

Operating Systems use three types of schedulers: long-term scheduler, short-term scheduler, and medium-term scheduler. The long-term scheduler decides which processes are admitted to the ready queue. It controls the degree of multiprogramming. The short-term scheduler (CPU scheduler) selects one process from the ready queue to execute. It runs frequently and must be very fast. The medium-term scheduler temporarily removes processes from memory (swapping) to reduce the load and improve performance. Each scheduler plays a specific role in balancing system performance, throughput, and responsiveness. Effective scheduling strategies improve resource utilization, minimize waiting time, and enhance user satisfaction.

10. What is the difference between multitasking, multiprocessing, and multithreading?

Multitasking refers to running multiple tasks (processes) on a single CPU by rapidly switching between them. Multiprocessing uses two or more CPUs to execute multiple processes simultaneously, truly in parallel. Multithreading is running multiple threads within a single process to perform concurrent operations. Multitasking improves user experience by enabling smooth application switching. Multiprocessing boosts performance by dividing tasks among processors. Multithreading optimizes resource sharing within a process and speeds up execution. While multitasking and multiprocessing involve processes, multithreading deals with threads. All three techniques enhance the efficiency and responsiveness of modern computer systems by effectively utilizing hardware and software resources.