Published: 18 Nov 2025 | Reading Time: 8 min read
An operating system (OS) is the most important software that controls the hardware and software parts of a computer and provides basic services to application programs. By managing the execution of software programs and performing operations such as memory allocation, I/O operations, and device management, it essentially is an intermediary between computer applications and the hardware. Understanding these basic ideas is vital while getting ready for an interview with operating system questions since the questions primarily concern the topics of OS features, resource management, and system efficiency.
This guide explains interview questions for OS and covers topics ranging from basic concepts to advanced functionalities, whether you are a fresher preparing for your first interview or an experienced professional looking to brush up on your knowledge.
Basic operating system interview questions concentrate on the fundamental concepts of operating systems. This section is created to test your learning of the basic principles, functions, and components of the OS.
Here are the essential basic OS interview questions:
An operating system (OS) is an interface between a user and computer hardware. It is software that manages computer hardware and provides services for software applications. The OS handles tasks such as allocating resources, managing processes, controlling memory, managing files, managing devices, and providing user interfaces. Examples include Windows, macOS, Linux, iOS, and Android.
Operating systems exist for two primary purposes: to ensure that a computer system performs well by managing hardware and software resources efficiently, and to provide an environment for the execution of programs.
The kernel is the core of an operating system. It manages system resources and allows communication between hardware and software components. The kernel operates in a privileged mode, controlling everything that occurs within the system.
Operating systems provide several essential services, including:
System calls are requests made by user programs to obtain services from the operating system. They provide an interface between user programs and the OS kernel, which allows access to hardware and OS functionalities.
When a computer is powered on, the BIOS executes a bootstrap program that loads the OS kernel into memory. This process is called booting. The kernel then initialises system components and starts necessary processes.
An open-source operating system is one whose source code is publicly available, allowing users to modify and distribute it. Examples include Linux and BSD UNIX.
A distributed operating system manages a group of independent computers, making them appear as a single system to users. It allows resource sharing and parallel processing across multiple nodes, making it a common topic in Operating System Interview Questions due to its significance in modern computing.
An operating system trap, also called an interrupt, is a mechanism that switches the system from user mode to kernel mode. This can happen due to an error or when a program requests a specific service from the operating system, such as accessing hardware or managing memory.
An operating system's main function is to oversee computer resources and keep the system working without any issues. It offers a convenient environment to the users in which applications can be run effectively. The OS takes care of the vital work of process scheduling, memory management, file storage, and security, thus making the computer trustworthy and high-performing.
RAID (Redundant Array of Independent Disks) is a technology used in operating systems to combine multiple physical disk drives into a single logical unit for data redundancy, performance improvement, or both. RAID can help protect data in case of hardware failures, improve read/write speeds, and increase storage capacity.
Common RAID Levels:
GUI (Graphical User Interface) is a user interface that allows users to interact with electronic devices using graphical icons, visual indicators, and other graphical elements, rather than typing text-based commands. A GUI makes it easier for users to interact with software or hardware because it uses images, buttons, and menus instead of text commands.
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Operating systems have evolved to meet a wide range of computing needs, from simple single-user tasks to complex, distributed environments. Understanding the various types of operating systems is crucial for choosing the right platform for specific applications and for excelling in technical interviews.
Batch operating systems were some of the earliest varieties of OS to be invented. Such systems run job batches requiring minimal user interaction. Users give jobs to the system, and it handles them one after another. While this method is excellent for situations where the same tasks need to be performed repeatedly, it is not capable of providing the response required by interactive applications.
A real-time operating system is an OS that handles applications requiring response to events immediately or within a predictable timeframe. Such systems are typical in embedded systems, e.g., medical devices that monitor vital signs, the control systems in vehicles, or industrial automation where independent operation and timing accuracy are essential.
Single-user OS is an operating system designed for a single user at a time thus most likely to be found in personal computers. Meanwhile, a multi-user operating system enables multiple users to share the system resources concurrently; those are the types of system used in servers and mainframes.
The multiprocessor OS is the software that supports a computer system structure topology that contains two or more central processing units (CPUs) that work together. The operating systems in question distribute tasks among the processors to raise the system's speed, fault tolerance, and throughput capability.
Distributed OS is software that operates a collection of networked, autonomous, and self-sufficient computers that look like a single integrated system to the users and the applications. This structure opens up possibilities for sharing of resources, balancing the load, and ensuring continuous operation in case of machine failures over the network. Distributed OSs provide the infrastructure necessary for cloud computing and large-scale enterprise systems.
Virtualizing technology offers a way for multiple OS installations to be operative at the same time on a single actual machine by providing a level of abstraction for the hardware resources. A hypervisor (also called a virtual machine manager) is a thin and specialized software layer that creates and manages the virtual machines, ensuring that they are isolated from each other and that shared physical hardware resources are given out efficiently. The technique is popular among data centers, cloud providers, and in the case of running embedded systems in a virtualized environment.
Effective process and thread management is critical for achieving multitasking, resource sharing, and overall system stability in modern operating systems. This section explores the lifecycle, structure, and coordination of processes and threads, as well as the key data structures and mechanisms used to manage them.
A process is an executing instance of a program, with its own address space, resources, and execution context. Each process transitions through several process states during its lifecycle, including:
The operating system maintains a process table, a data structure that keeps track of all active processes. Each entry in this table is a Process Control Block (PCB), which contains vital information such as:
Processes move between different queues based on their state:
The OS scheduler selects processes from these queues for execution, enabling efficient CPU utilization and multitasking.
Context switching is the process of saving the state of the currently running process and loading the state of the next process to run. This mechanism enables multiple processes and threads to share the CPU, allowing for multitasking and responsive system behaviour. However, frequent context switching can incur performance overhead.
A thread is the minimum level of CPU a process can be divided into. Threads from the same process can share the code, data, and resources, but each thread possesses its own program counters and stack. With the help of multithreading, several threads can be executed at the same time in one process which consequently leads to better resource utilization, an increase in the speed of the application, and the facilitation of parallelism.
Processes and threads often need to coordinate or exchange data. Inter-process communication (IPC) mechanisms—such as message passing, shared memory, and pipes—enable safe and efficient data exchange and synchronization between processes.
The resource allocation graph is a visual representation of resource assignments and requests among processes. It is a valuable tool for detecting and preventing deadlocks, ensuring that resources are allocated safely and efficiently.
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These interview questions for OS are based on the core principles and functionalities of operating systems. They go beyond the basic operating system interview questions, testing your learning of how an OS manages hardware and software resources.
A process is an active program currently being executed by the CPU. It resides in the main memory and continuously changes its state as it runs.
A thread is the smallest unit of execution within a process. Unlike a process, threads share resources such as memory, but each has its own stack and registers.
In a paging system, physical memory is divided into fixed-size blocks called frames, while virtual memory is divided into pages of the same size. The OS maps pages to frames to manage memory allocation efficiently.
Multiprogramming allows multiple programs to run on a single CPU by switching between them. This improves CPU utilization and increases system throughput, which allows more tasks to be completed in less time.
Virtual memory is a technique that extends a computer's physical memory by using a part of the hard drive as additional RAM. This allows large programs to run even if the system doesn't have enough physical memory.
The OS keeps track of memory usage and allocates space to programs as needed. When a program no longer requires memory, the OS reclaims and redistributes it to other processes for efficient utilization. Learning how memory management works is essential when preparing for Operating System Interview Questions.
A CPU scheduler selects which process in the ready queue should execute next. It makes scheduling decisions whenever a process switches states, such as when it moves from running to waiting or terminates.
A dispatcher hands control of the CPU to the process selected by the scheduler. It performs tasks such as context switching, switching to user mode, and starting the following process. The time taken for this transition is referred to as dispatch latency.
Demand paging is a memory management technique where pages are loaded into RAM only when needed. This reduces memory usage and speeds up execution by avoiding unnecessary page loading.
The booting process begins when you turn on the computer. The system loads the OS kernel into memory and initializes hardware components. If the system encounters issues, it boots into safe mode to troubleshoot problems.
Operating systems manage hardware and software resources, providing an interface for users. Some widely used examples are:
Fragmentation occurs when disk or memory space is broken into small, non-contiguous pieces, making it harder for the system to read or write data efficiently.
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Efficient CPU scheduling is at the core of elevating the performance level of a system and optimizing resource utilization in an operating system. Scheduling algorithms decide the order of execution of processes on the CPU, thus they are the main factors for system responsiveness, throughput, and fairness.
The main goals of CPU scheduling are to keep the CPU busy as much as possible, reduce the waiting and turnaround times, and ensure that all processes get fair treatment. Load balancing at its best contributes to the even distribution of workloads over the system resources.
Several CPU scheduling algorithms are used, each with distinct strategies:
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These advanced interview questions for os examine more in-depth concepts related to basic operating system interview questions and focus on how they function and manage resources efficiently.
The exec() system call replaces the memory space of a running process with a new program. It is commonly used after a process is created using the fork() function. The new program is specified as a parameter in the exec() call, and once executed, it replaces the existing process image.
A parent process uses the wait() system call to pause its execution until a child process finishes running. Once the child process terminates, the parent receives its process ID (PID) and exit status. This helps in proper process synchronization and prevents orphan processes.
Multiprocessor OS enables a system to run faster by the use of multiple CPUs. Some of the most significant benefits are:
A real-time system processes tasks within a strict time frame. It is used in applications where timely execution is necessary, such as medical devices, automotive control systems, and industrial automation. These systems adhere to predefined time constraints to ensure predictable performance.
A socket is an endpoint for communication between two processes over a network. It enables data exchange between processes running on the same machine or different machines connected via a network.
Starvation occurs when a process waits indefinitely for resources because other processes with higher priority keep getting access first. To prevent starvation, scheduling techniques such as ageing gradually increase the priority of waiting processes, ensuring they eventually receive the required resources.
Multithreading allows multiple threads to run within a single process, which shows several advantages:
The OS translates logical addresses into physical addresses using memory management techniques like paging and segmentation.
Overlays enable programs that exceed available memory to run efficiently. This technique loads only the necessary parts of a program into memory while keeping the rest on disk. It helps optimize memory usage in constrained environments.
Modern operating systems must manage multiple processes that compete for shared resources. Two key challenges in this area are preventing deadlocks and ensuring proper synchronization.
A deadlock occurs when two or more processes are unable to proceed because each is waiting for a resource held by the other. Four necessary conditions must be present for a deadlock to occur:
In order to keep data consistent and avoid race conditions, several synchronization mechanisms are used:
Proper resource allocation is crucial for both deadlock avoidance and synchronization. A safe state is a situation where the system can allocate resources to every process in some order without leading to a deadlock.
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File and storage management is a core responsibility of modern operating systems, ensuring that data is stored, retrieved, and protected efficiently. This area covers file systems, storage allocation methods, redundancy strategies, and the mechanisms that optimize data access and reliability.
A file system organises and manages the storage and retrieval of data on storage devices. It provides a structure for storing files, directories, and metadata, enabling operations such as creation, deletion, reading, writing, and modification.
The way files are stored on disk affects performance and reliability. One common approach is the File Allocation Table (FAT), which tracks the location of each file's data blocks or clusters on the disk. Clusters are the fundamental units of disk storage, and efficient allocation helps minimise fragmentation and improve access speed.
RAID (Redundant Array of Independent Disks) is a method that links several physical disks together to form a single logical unit with features like increased performance, larger storage capacity, and data redundancy. Some of the common RAID concepts are:
Bottom Line: RAID levels, such as RAID 0 (striping), RAID 1 (mirroring), and RAID 5 (striping with parity), offer different balances of performance, capacity, and fault tolerance.
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A deadlock happens when two or more processes get stuck indefinitely because each is waiting for the other to release a resource. Since none of them can proceed, the system reaches a standstill.
A time-sharing system is a type of multitasking operating system that quickly switches between multiple users, giving each a short time slice to execute their tasks. This creates the illusion that all users are working. Time-sharing systems are crucial when preparing for Operating System Interview Questions, as they are an essential concept in modern computing.
A monolithic kernel keeps all essential operating system services, such as memory management, file system, and device drivers, within the kernel itself. This results in faster performance but can make debugging and updates more complex.
A microkernel, on the other hand, only contains the core functionalities, like inter-process communication and basic scheduling. Other services run in user space, making the system more modular and secure but slightly slower due to increased communication overhead.
Context switching is when the CPU saves the state of a running process and loads the state of another process. This allows multiple processes to share the CPU efficiently. It occurs in multitasking environments whenever the OS needs to switch from one method to another.
An interrupt is a signal sent to the processor to indicate that an urgent event needs attention. It helps the OS prioritise important tasks, such as responding to user input or handling hardware failures, without constantly checking for these events.
Operating systems use various memory management techniques to allocate and optimise memory:
Thrashing occurs when a system spends more time swapping data between RAM and disk (paging) than executing actual processes. This happens when there isn't enough RAM, resulting in excessive page faults. To prevent thrashing, you can:
A race condition occurs when multiple processes access and modify shared data simultaneously, leading to unpredictable results. This happens in concurrent programming when proper synchronisation mechanisms are not employed.
The Banker's Algorithm is a method used to prevent deadlocks by ensuring that resource allocation remains in a safe state. It is a common topic in Operating System Interview Questions. Before assigning resources to a process, the algorithm checks whether it is still possible to meet the needs of all processes without encountering a deadlock. If granting resources could cause a deadlock, the request is rejected or delayed.
| Aspect | Multitasking OS | Multiprocessing OS |
|---|---|---|
| Definition | Allows multiple tasks to run concurrently on a single CPU by rapidly switching between them | Uses multiple CPUs or cores to execute multiple processes simultaneously |
| CPU Usage | Single CPU switches between tasks | Multiple CPUs work in parallel |
| Performance | Limited by single CPU speed | Higher performance due to parallel processing |
| Example | Windows, Linux running multiple applications | Systems with multi-core processors |
A zombie process is a process that has completed execution but remains in the process table because its parent has not read its exit status.
Reentrancy refers to code or functions that can be safely executed by multiple tasks or interrupt routines simultaneously without causing conflicts.
A reentrant function:
Used in OS kernels, interrupt handlers, and multithreading for safety.
Modern operating systems incorporate several advanced concepts to improve efficiency, reliability, and security. Understanding these topics can help you excel in technical interviews that probe beyond the basics.
Reentrancy is a property of code that allows multiple processes or threads to execute the same function simultaneously without causing data corruption or unexpected behaviour. A reentrant function does not modify shared or static data and uses only local variables for its operations. This is especially important in kernel space, where interrupt handlers or concurrent routines may need to call the same function. Reentrant code is essential for safe process management and is widely used in system libraries and OS kernels.
Spooling (Simultaneous Peripheral Operations Online) is a technique where data destined for peripherals—such as printers or disk drives—is temporarily stored in a buffer or queue. This allows the operating system to manage scheduling efficiently and prevents slower devices from blocking faster processes. By decoupling the speed of the CPU from that of I/O devices, spooling improves overall system performance and ensures asynchronous operation between components.
Bootstrapping is the process that loads the operating system into memory when the computer is powered on. It begins with the power-on self-test (POST), which checks hardware integrity. The system then executes a small program stored in firmware (the bootstrap loader), which loads the OS kernel into memory. This transition from firmware to the whole operating system involves initializing memory allocation, setting up process management structures, and preparing user space and kernel space for operation.
SMP is an architecture wherein two or more processors utilize a shared memory and run under a single OS instance. Any processor can utilize the system resources, such as the memory and the I/O devices, in parallel to each other as the processors have equal access to them. The OS's scheduling algorithms take the different work units and assign them to different CPUs thus resulting in increased throughput, reliability, and responsiveness. To achieve optimal performance, SMP systems must be highly efficient in memory allocation and process management.
To keep and improve efficiency, operating systems also use very detailed measures such as CPU utilization, memory usage, disk I/O rates, and process scheduling efficiency. Access-control lists and user-allowed permissions are mechanisms that help secure resource usage, whereas transmission isolation is used to protect data transfers between the user space and kernel space. Regularly checking these measures gives system administrators the opportunity to identify the limits, use peripherals competently, and implement security policies.
Quick Note: Reentrancy ensures thread-safe code; spooling decouples I/O speed; bootstrapping initializes kernel; SMP enables true parallelism; metrics + access control drive secure, high-performance OS.
A real-time operating system (RTOS) refers to a specially designed OS that is geared towards the situations where the completion of the tasks within specified time frames is a must. It guarantees the resolutions of the most important issues in a timely manner and thus, is the most suitable choice for the systems whose operation is heavily dependent on time, such as medical devices, industrial automation, embedded systems, etc.
The features of an RTOS include:
RTOS can be classified depending on their deadline enforcement strictness:
RTOS brings in a number of advantages:
Instead of its advantages, RTOS comes with some challenges:
Bottom Line: RTOS ensures timely execution hard deadlines prevent failure soft allows delay offers low latency reliability but needs expertise optimization and complex debugging
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When preparing for an Operating System Interview Questions. A solid understanding of operating system topics, as well as an understanding of how operating systems function, helps in answering technical questions effectively. Here are the core areas to study.
Operating systems are responsible for controlling processes that involve tasks such as creating, running, and deleting processes. Figuratively, processes are said to have three different states: ready, running, and waiting. The operating system uses a Process Control Block (PCB) to keep track of each process. Scheduling algorithms, e.g. First-Come-First-Served (FCFS), Round Robin, and Shortest Job Next (SJN,) are used to decide which method should be given CPU time.
Memory management must be highly efficient to prevent programs from crashing and interfering with each other. Operating systems achieve this by means of paging and segmentation techniques. Additionally, virtual memory allows the use of disk space as an extension of RAM, so that the running of large applications will not exhaust the physical memory.
A file system is a method that helps keep data organized and manageable, which is saved on a disk. It also provides a systematic way to store and fetch files through the use of directories and indexing. Different file systems, including NTFS, FAT32, and ext4, differ regarding their structures and features. Primary file operations include reading, writing, creating, and deleting a file.
Through multiprogramming, current operating systems are capable of carrying out multiple tasks concurrently, rendering the management of concurrency a must-have skill. To ensure data consistency when a shared resource is accessed by various processes synchronization tools, such as semaphores, mutexes, and condition variables are employed. Deadlocks, which occur when processes wait for each other and thus come to a halt, can be prevented or resolved using methods such as resource ordering and the banker's algorithm.
The CPU sends I/O commands to other peripheral devices, such as printers, disk drives, and keyboards. An operating system manages input/output (I/O) devices by utilising device drivers and scheduling methods. Polling, interrupts, and Direct Memory Access (DMA) are the different techniques used to handle I/O requests in efficient manners.
An operating system helps ensure security by letting in only authorized users, thus, unauthorized ones not being able to access confidential data or interfere with the operations of the system. Security provisions that are actively implemented include access control, credential verification, and permission granting. Firewalls, encryption methods, and intrusion detection systems are the ways that protect users from cyber threats.
Virtualisation is a technology that enables multiple operating systems to run on a single physical machine by utilising virtual machines. The management of the different VMs is performed by a hypervisor that serves as an abstraction layer between hardware and software. Virtualization raises resource efficiency, bolsters security, and makes possible cloud computing. Apart from that, virtualization is also a significant topic in operating system interviews.
Real-time operating systems or just RTOS are found in scenarios where the execution of the tasks should be on time at any cost. Examples are medical equipment, automotive systems, and industrial automation. RTOS strictly adhere to scheduling algorithms such as Rate Monotonic Scheduling (RMS) and Earliest Deadline First (EDF) to make sure the execution of time-critical tasks is done on time.
A distributed system is a collection of separate computers that collaborate for the production of a service. These systems communicate with each other via client-server and peer-to-peer models. Distributed file systems, fault-tolerance mechanisms, and distributed synchronisation techniques facilitate the management of resources spread across various nodes.
The kernel is basically a single unit that is made up of various components and is the main part responsible for handling the hardware and the rest of the system resources of the OS. System calls are the main functions that the kernel is in charge of executing, thus enabling user apps to function in hardware interaction. Besides that, the kernel management stack also features memory management, process management, file systems, and device drivers. Types of kernel designs range from monolithic kernels, microkernels, and hybrid kernels to name a few with each set having its own pros and cons.
Preparing for operating system interview questions requires a solid understanding of core concepts and consistent practice in answering questions and solving problems. Begin by reviewing the fundamentals, ensuring you have a clear understanding of concepts such as process management, memory management, and file systems.
Practicing OS-related questions from basic to advanced helps in strengthening problem-solving skills. Try to include real-world examples to indicate your understanding of concepts like scheduling algorithms, deadlock prevention, and virtualization. Utilizing online resources, such as tutorials, articles, and discussion forums, can also supplement your learning and clarify complex topics.
Mock interviews with friends or colleagues are a great way to simulate a real interview environment and receive constructive feedback. Staying updated on the latest OS developments and related technologies can also give you an edge. During the interview, remain calm, confident, and focused.
To succeed in computer science or IT, you need a strong grasp of operating systems, which will help you build a solid understanding. Studying Operating System Interview Questions can enhance your preparation by covering key areas like process management, memory management, and real-time systems. With consistent practice, you'll gain the confidence to showcase your skills effectively.
Operating Systems control every device and cloud service in 2025. Mastering OS concepts is mandatory for high-paying roles in systems programming, cloud infrastructure, embedded/RTOS, kernel development, and BigTech interviews (Google, Meta, Apple) where OS questions decide offers and packages above $150K–$300K.
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