Operating System Interview Questions
Embarking on a journey into the realm of operating systems, whether as a seasoned professional or a fresh-faced candidate, can be both exhilarating and daunting. As the foundational software that manages computer hardware resources and provides services for computer programs, operating systems play a pivotal role in the digital landscape. In the realm of job interviews, particularly in the tech industry, demonstrating a solid understanding of operating systems is often a prerequisite. To help you navigate this terrain with confidence, we’ve compiled a comprehensive list of key operating system interview questions designed to test your knowledge, problem-solving abilities, and analytical skills.
From the basics of process management and memory allocation to the intricacies of file systems and security mechanisms, operating system interview questions cover a broad spectrum of topics. Employers seek candidates who can articulate concepts clearly, apply theoretical knowledge to practical scenarios, and showcase critical thinking in solving complex problems. Whether you’re preparing for an entry-level position or aiming for a senior role, mastering these interview questions will not only enhance your chances of success but also deepen your understanding of the foundational principles that underpin modern computing systems. So, let’s delve into the world of operating systems, unravel its mysteries, and equip ourselves with the knowledge and confidence to ace those interviews.
What do you mean by an operating system? What are its basic functions?
An operating system (OS) is a fundamental software program that oversees and organizes a computer’s resources, including both hardware and software components. Originating in the early 1950s, the first recognized OS, known as GMOs, paved the way for subsequent developments in computing. Operating systems serve as intermediaries between computer users and the underlying hardware, facilitating the efficient utilization and coordination of resources.
Key Functions of an Operating System:
The OS fulfills various essential functions to ensure the smooth operation of a computer system:
- Managing memory and processor resources effectively.
- Providing a user-friendly interface for interacting with the computer system.
- Handling file and device management tasks, including storage and peripheral devices.
- Scheduling resources and tasks to optimize performance and throughput.
- Detecting and managing errors to maintain system stability and reliability.
- Implementing security measures to safeguard data and protect against unauthorized access.
Why is the operating system important?
The operating system (OS) serves as a fundamental component of a computer, rendering it functional and purposeful. It facilitates an interface through which users interact with installed software, bridging the gap between human input and computer operations. Additionally, the OS facilitates communication with hardware components while ensuring optimal resource allocation between hardware and the central processing unit (CPU). Beyond its foundational role, the OS furnishes users with essential services and serves as a platform for executing programs, handling a spectrum of tasks commonly required by applications.
What's the main purpose of an OS? What are the different types of OS?
The primary function of an operating system (OS) is to execute user programs and facilitate user-computer interaction while also optimizing system performance by overseeing computational tasks. It handles various aspects of computer operation including memory management, process control, and coordination of hardware and software functions.
Different categories of operating systems include:
- Batch Processing OS (e.g., Payroll Systems, Transaction Processing)
- Multi-Programmed OS (e.g., Windows, UNIX)
- Time-Sharing OS (e.g., Multics)
- Distributed OS (e.g., LOCUS)
- Real-Time OS (e.g., PSOS, VRTX)
What are the benefits of a multiprocessor system?
A Multiprocessor system consists of two or more CPUs, which can concurrently process multiple computer programs. These CPUs share a single memory, enabling the execution of several tasks simultaneously.
Benefits:
- These systems are increasingly adopted to enhance performance in environments where multiple programs run concurrently.
- The addition of processors allows for more tasks to be completed within a given timeframe.
- There’s a significant boost in throughput, and since all processors share resources, it’s cost-effective.
- Overall, multiprocessor systems enhance the reliability of computer systems.
What is RAID structure in OS? What are the different levels of RAID configuration?
RAID (Redundant Arrays of Independent Disks) serves as a method for distributing data across multiple hard disks, offering a form of data storage consolidation. It effectively balances considerations like data protection, system performance, and available storage space. By leveraging RAID, organizations aim to enhance the overall reliability and performance of their data storage systems while also expanding storage capacity and mitigating the risk of data loss.
There exist several RAID configurations, each tailored to different priorities and requirements:
- RAID 0: Focuses on performance enhancement through non-redundant striping.
- RAID 1: Implements disk mirroring for basic fault tolerance.
- RAID 2: Utilizes memory-style error-correcting codes, typically employing dedicated hamming code parity.
- RAID 3: Involves bit-interleaved parity, necessitating a dedicated drive for storing parity information.
- RAID 4: Similar to RAID 5 but consolidates all parity data onto a single drive.
- RAID 5: Offers improved performance compared to disk mirroring and incorporates distributed parity for fault tolerance.
- RAID 6: Features P+Q redundancy, providing fault tolerance for up to two drive failures.
What is GUI?
A Graphical User Interface (GUI) serves as a user-friendly interface that utilizes graphics for interaction with an operating system. It was developed to simplify user interaction compared to traditional command-line interfaces, making it less intricate and more intuitive. Its primary objective is to enhance efficiency and user-friendliness. Rather than requiring users to memorize commands, a GUI allows them to execute tasks by clicking buttons or icons. Examples of GUIs include Microsoft Windows, macOS, and Apple’s iOS.
What is a Pipe and when it is used?
The pipe serves as a link between two or more related processes, enabling communication between them through message passing. It facilitates the transmission of data, such as the output of one program, to another program. Pipes are particularly useful for one-way communication between processes, known as inter-process communication (IPC).
What are the different kinds of operations that are possible on semaphore?
There are basically two atomic operations that are possible:
- Wait()
- Signal()
What is a bootstrap program in OS?
It’s essentially a program responsible for kicking off the operating system when a computer starts up. This program, often called booting, initiates a bootstrapping process that loads the OS. The OS relies solely on this bootstrap program to function properly. Typically, the bootstrap program is stored in fixed locations on the disk known as boot blocks. Its main task is to find the kernel and transfer it to the main memory, from where it can begin executing.
Explain demand paging?
Paging on demand is a technique for loading pages into memory only when needed, commonly employed in virtual memory systems. Instead of loading entire pages preemptively, this approach waits until a specific location on a page is accessed during program execution. The process generally involves the following steps:
- Attempting to access the page.
- If the page is already in memory (valid), the instructions continue executing as usual.
- If the page is not in memory (invalid), a page-fault trap is triggered.
- Verifying if the memory reference is valid and pointing to a location in secondary memory. If not, the process is halted due to illegal memory access. If valid, the required page needs to be loaded.
- Scheduling a disk operation to read the required page into the main memory.
- Resuming the interrupted instruction that caused the operating system trap.
What do you mean by RTOS?
A Real-Time Operating System (RTOS) serves the purpose of managing real-time applications, which require data processing to occur within precise and consistent timeframes. It excels in handling tasks with strict timing constraints, ensuring reliable performance for critical operations. In addition to overseeing execution and monitoring processes, an RTOS is adept at resource management, optimizing efficiency within limited memory and resource constraints.
There are several classifications of RTOS based on the degree of timing stringency they offer:
- Hard Real-Time: Ensures that tasks are completed within their specified time constraints without exceptions, prioritizing deterministic behavior for mission-critical applications.
- Firm Real-Time: Guarantees timely completion of tasks under normal conditions, with occasional permissible delays, providing a balance between strict timing requirements and flexibility.
- Soft Real-Time: Prioritizes responsiveness and timely completion of tasks, but allows for occasional delays without compromising overall system functionality, suitable for applications where timing constraints are less stringent.
What do you mean by process synchronization?
Process synchronization involves coordinating processes that utilize shared resources or data. Its primary objective is to ensure the synchronized execution of cooperating processes, thereby maintaining data consistency. The main purpose is to facilitate the sharing of resources without interference, achieved through mutual exclusion. Process synchronization can be categorized into two types:
- independent processesÂ
- cooperative processes.
What is IPC? What are the different IPC mechanisms?
Interprocess Communication (IPC) is a method that utilizes shared resources, such as memory, to enable communication between processes or threads within an operating system. Through IPC, the OS facilitates communication among various processes, enabling the exchange of data. This mechanism serves to facilitate the sharing of information between multiple threads across one or more programs or processes, with the operating system overseeing the interaction.
Various IPC mechanisms include:
- Pipes
- Message Queuing
- Semaphores
- Sockets
- Shared Memory
- Signals
What is different between main memory and secondary memory.
Main Memory: Primary memory, often referred to as main memory or RAM (Random Access Memory), serves as the immediate storage space for programs and data required by the CPU during program execution. It enables swift access to information, facilitating efficient processing within the computer system.
Secondary memory: Secondary memory encompasses various storage devices designed to retain data and programs over extended periods. Commonly known as external memory, these storage solutions include hard drives, USB flash drives, CDs, and more. Unlike primary memory, secondary memory devices excel in storing large volumes of data, offering a reliable backup and additional storage capacity for the computer system.
What do you mean by overlays in OS?
Overlays represent a programming technique aimed at breaking down processes into smaller segments, allowing crucial instructions to be stored in memory. This method operates independently of the operating system and enables the execution of programs larger than the available physical memory. By selectively retaining essential data and instructions required at any given moment, overlays efficiently manage memory usage.
Write top 10 examples of OS?
Some of the top OS’s that are used mostly are given below:
- MS-Windows
- Ubuntu
- Mac OS
- Fedora
- Solaris
- Free BSD
- Chrome OS
- CentOS
- Debian
- Android
What is virtual memory?
This feature in an operating system manages memory without users needing to be aware, giving the impression of a larger main memory. Essentially, it’s a space where numerous programs can reside independently in the form of pages, facilitating the storage of more programs. This approach optimizes physical memory utilization by utilizing disk space and also ensures memory protection. Typically, operating systems manage this through two methods: paging and segmentation. It serves as a temporary storage area, supplementing RAM for computer processes.
What is thread in OS?
A thread represents a sequence of tasks executed within a program, comprising essential components like a program counter, thread ID, stack, and registers. Threads facilitate efficient communication and utilization of CPU resources, especially in systems with multiple processors. They enhance performance by enabling parallel execution of tasks, thereby reducing the overhead associated with context switching. Threads, often referred to as lightweight processes, possess individual stacks while being capable of accessing shared data.
Within a process, multiple threads share various resources, including the address space, heap, static data, code segments, file descriptors, global variables, child processes, pending alarms, signals, and signal handlers. Despite this shared environment, each thread maintains its distinct program counter, registers, stack, and state, allowing for independent execution and management of tasks.
What is a process? What are the different states of a process?
A process refers to a program that is currently active and running on a computer system. The primary role of an operating system (OS) is to oversee and manage these processes effectively. Once a program is loaded into the system’s memory and begins execution, it is divided into four sections: stack, heap, text, and data. Processes are broadly categorized into two types:
- those initiated by the operating system itselfÂ
- those initiated by users.
States of Process:
- New State: This marks the creation of a process.
- Running: At this stage, the CPU executes the instructions of the process.
- Waiting: The process enters this state when it awaits a particular event before it can proceed.
- Ready: In this state, the process possesses all necessary resources for execution but awaits assignment to a processor, typically because all CPUs are currently engaged.
- Terminate: When a process completes its execution, it transitions into the termination state, signifying its conclusion.
What do you mean by FCFS?
FCFS (First Come First Serve) is a straightforward operating system scheduling algorithm that prioritizes processes based on their arrival time. Put simply, the first process to arrive is the first to be executed, following a non-preemptive approach. However, FCFS scheduling may lead to the issue of starvation if the initial process has the longest execution time among all jobs. In this context, burst time refers to the duration, measured in milliseconds, required by a process for completion. Widely regarded as the most basic and uncomplicated scheduling algorithm, FCFS is commonly implemented using a FIFO (First In First Out) queue.
What is Reentrancy?
Reentrancy refers to a function that allows multiple clients to utilize and access a single instance of a program concurrently. This concept primarily pertains to operating system code and doesn’t involve dealing with simultaneous execution. It serves two primary purposes:
- The program code remains static and doesn’t alter itself.
- Each client process must store its local data separately, typically on distinct storage disks.
What is a Scheduling Algorithm? Name different types of scheduling algorithms.
A scheduling algorithm is a method employed to enhance efficiency by making the most of CPU usage while minimizing task waiting times. It tackles the challenge of determining which pending requests should receive resources. Its primary goal is to alleviate resource shortage and uphold fairness among parties vying for resources. Essentially, it assigns resources among different competing tasks.
Types of Scheduling Algorithm
There are different types of scheduling algorithms as given below:
- First Come First Serve
- Priority Scheduling
- Shortest Remaining Time
- Shortest Job First
- Round Robin Scheduling
- Multilevel Queue Scheduling
What is the difference between paging and segmentation?
Paging: Paging serves as a memory management method enabling the operating system to fetch processes from secondary storage into primary memory. It employs a non-continuous allocation strategy by breaking down each process into pages.
Segmentation: Segmentation is a memory management approach that organizes processes into various-sized modules and segments. These segments, which comprise distinct parts of a process, can be allocated individually.
What is thrashing in OS?
This situation arises when the CPU is engaged in less efficient tasks like swapping or paging instead of productive work. The system can identify this state by assessing CPU utilization levels, indicating thrashing. Thrashing happens when a process lacks sufficient pages, leading to a higher rate of page faults. Consequently, this hampers application-level processing, resulting in degraded or even collapsed computer performance.
What is the main objective of multiprogramming?
Multiprogramming enables the execution of multiple programs on a single processor machine, addressing the issue of CPU and main memory underutilization. Essentially, it involves coordinating the simultaneous execution of various programs on a single CPU. The primary aim of multiprogramming is to ensure that there are always some processes running, thereby enhancing CPU utilization. By organizing multiple jobs, multiprogramming ensures that the CPU consistently has tasks to execute, thus optimizing its efficiency.
What do you mean by asymmetric clustering?
Asymmetric Clustering operates by designating one node as a standby while the remaining nodes run various applications. This approach utilizes all available hardware resources, contributing to its reputation for reliability compared to alternative systems.
What is the difference between multitasking and multiprocessing OS?
Multitasking: Multitasking enhances computer hardware utilization by handling multiple tasks simultaneously, swiftly switching between them. These systems are also referred to as time-sharing systems.
Multiprocessing: Multiprocessing involves employing multiple processors within a computer to concurrently process different segments of a program. This approach boosts productivity by completing tasks more swiftly.
What do you mean by Sockets in OS?
In operating systems, a socket serves as a point of connection for Interprocess Communication (IPC). Essentially, it combines an IP address with a port number to establish this connection. Software developers utilize sockets to streamline the creation of network-capable applications, facilitating the exchange of data between processes, whether they reside on the same machine or different ones. This functionality finds frequent applications in systems structured around client-server architectures.
Types of Sockets
There are four types of sockets as given below:
- Stream Sockets
- Datagram Sockets
- Sequenced Packet Sockets
- Raw Sockets
Explain zombie process?
A “zombie process,” also known as a defunct process, occurs when a process has finished its task or has been terminated, but its process control block remains in the main memory because it’s still listed in the process table to report back to its parent process. Despite being inactive and consuming no resources, the zombie process persists, indicating that resources are being held by a process that has already completed its execution.
What do you mean by cascading termination?
Cascading termination refers to a process-ending scenario where when the parent process concludes its operation, the associated child processes also cease to function. This mechanism prevents child processes from persisting after their parent process has terminated. Typically, it is activated by the operating system (OS).
What is starvation and aging in OS?
When utilizing Priority Scheduling or Shortest Job First Scheduling, the issue of Starvation may arise, particularly in CPU schedulers.
Starvation occurs when a process is unable to access the necessary resources for an extended period, leading to a backlog of low-priority processes while high-priority ones continue to progress. This results in insufficient resource allocation for low-priority tasks.
Aging serves as a solution to the problem of starvation by adjusting the priority of processes waiting for resources over prolonged durations. This technique mitigates starvation by introducing an aging factor to prioritize resource requests, ensuring that low-priority processes eventually receive the resources they require. Moreover, Aging facilitates the completion of tasks in lower-priority queues or processes.
What do you mean by Semaphore in OS? Why is it used?
Semaphore serves as a synchronization mechanism essential for regulating access to shared resources in systems with multiple threads or processes. It manages a count of available resources and offers two fundamental operations: wait() and signal(). Moreover, it can possess a count higher than one, enabling it to govern access to a fixed pool of resources.
Varieties of Semaphores
Semaphores primarily exist in two forms:
Binary semaphore: This synchronization tool operates with only two possible values: 0 and 1. Its purpose is to indicate the availability of a singular resource, like a shared memory location or a file.
Counting semaphore: Unlike its binary counterpart, a counting semaphore can hold a value exceeding 1. It serves to regulate access to a finite quantity of resources, such as a pool of database connections or a restricted number of threads.
What is Kernel and write its main functions?
The kernel serves as a fundamental program within an operating system (OS), functioning as a central hub for managing computer operations and hardware. Upon system startup, the kernel is loaded into the main memory, assuming a pivotal role in coordinating various system functions. Acting as a mediator between user applications and hardware components, it facilitates seamless interactions while ensuring efficient resource allocation.
Key Responsibilities of the Kernel:
- Resource Management: The kernel oversees the allocation and utilization of essential computer resources, including CPU, memory, files, and processes.
- Hardware-Software Interface: It facilitates communication and coordination between hardware and software components, enabling them to work in harmony.
- Memory Management: Efficient management of RAM is ensured to optimize the performance of running processes and programs.
- System Control: The kernel governs core OS tasks and regulates access to peripherals connected to the computer.
- CPU Scheduling: It orchestrates the execution of tasks by the CPU, prioritizing user workloads to enhance overall system efficiency.
What are different types of Kernel?
There are five types of Kernels as given below:
- Monolithic Kernel
- MicroKernel
- Hybrid KernelÂ
- Nano Kernel
- Exo Kernel
Write difference between micro kernel and monolithic kernel?
MicroKernel: A microkernel is a streamlined operating system that focuses solely on essential functions. It includes only the fundamental features necessary for operating systems to function. Examples include QNX, Mac OS X, and K42.
Monolithic Kernel: In contrast, a monolithic kernel encompasses all the fundamental features required for managing computer components, including resource management, memory, and file systems. Examples of operating systems utilizing this architecture include Solaris, DOS, OpenVMS, and Linux.
What is SMP (Symmetric Multiprocessing)?
Symmetric multiprocessing (SMP) refers to a computer architecture where multiple processors collaborate under a single operating system (OS) and memory setup. SMP becomes essential when leveraging hardware with multiple processors. Its fundamental function allows any processor to handle tasks regardless of the data or resources’ location in memory. As a result, SMP systems offer enhanced reliability compared to their single-processor counterparts.
What is a time-sharing system?
It’s a system enabling multiple users to access a system’s resources from various places. Put plainly, it handles multiple tasks on a single processor or CPU by dividing time among different processes. This arrangement facilitates simultaneous usage of a computer system by different users from diverse locations, making it a significant type of operating system.
What is Context Switching?
Context switching is essentially the act of preserving the current state of one process while loading the state of another. It’s a practical and efficient method employed by CPUs to enable multiple processes to utilize a single CPU, thus optimizing time and resources. This functionality is integral to modern operating systems, facilitating the transition of processes between different states, such as from a running state to a ready state. Moreover, it empowers a solitary CPU to manage numerous processes or threads seamlessly, eliminating the necessity for extra resources.
What is difference between Kernel and OS?
Kernel: The kernel serves as a fundamental system program responsible for managing all running programs on a computer. Acting as a mediator between the software and hardware components, it facilitates their interaction.
Operating System: The operating system, another essential system program, operates on a computer to offer users an interface for smooth interaction with the system. Its purpose is to simplify computer operation for users.
What is difference between process and thread?
Process: A process refers to an active program that is currently running on one or more threads within the operating system. It holds significant importance in today’s operating systems.
Thread: A thread represents a sequence of execution within a process, comprising essential components such as the program counter, thread ID, stack, and a collection of registers.
What are various sections of the process?
The process consists of four main sections outlined below:
- Stack: This section handles local variables and return addresses.
- Heap: It manages dynamic memory allocation.
- Data: Here, global and static variables are stored.
- Code or text: This segment contains the compiled program code.
What is a deadlock in OS? What are the necessary conditions for a deadlock?
Deadlock typically arises when a group of processes becomes stuck due to each process holding resources while awaiting resources held by another process. In such a scenario, multiple processes attempt to execute concurrently but are forced to wait for each other to complete their execution due to interdependency. The occurrence of a deadlock manifests as a halt in the system, highlighting a fundamental issue within the program. This issue is frequently encountered in multiprocessing environments.
Necessary Conditions for DeadlockFour essential conditions contribute to the occurrence of deadlock:
- Mutual Exclusion
- Hold and Wait
- No Pre-emption
- Circular Wait or Resource Wait
What do you mean by Belady’s Anomaly?
In an operating system, data processing involves loading data in predetermined units known as pages. These pages are then stored in fixed-size sections of memory referred to as frames by the processor. Belady’s Anomaly is observed when increasing the number of frames in memory leads to a rise in page faults. This phenomenon typically occurs when employing the FIFO (First in, First out) page replacement algorithm.
What is spooling in OS?
Spooling, short for Simultaneous Peripheral Operations Online, involves storing data from different input/output tasks in a designated buffer area, typically located in memory or on a hard disk. This buffer serves as an intermediary between a computer program and a slower peripheral device. Its primary purpose is to manage the varying data transfer rates between devices, facilitating smooth communication.
Utilizing spooling is crucial due to the disparate speeds at which devices can access or transmit data. By employing this technique, the system can optimize efficiency by overlapping input/output operations with processor tasks. Additionally, spooling often utilizes the disk as a large storage buffer, further enhancing its capacity to manage data transfer effectively.
