An Operating System (OS) enables computer software to interact and function with computer hardware. An operating system is an intermediary graphical user interface (GUI) between the user and the computer system. An operating system mediates between the user and the computer hardware, overseeing resources like memory, processing power, and input/output processes. Examples of popular operating systems are Windows, MacOS, Linux, and Android.

This article presents multiple OS interview questions and answers, ranging from fundamental OS architecture to advanced concepts like file systems, scheduling algorithms, and multithreading. This article guides entry-level and seasoned IT professionals to excel in their following operating system interviews.

Basic Operating System Interview Questions

Define process and process table.

A process is a program that is currently running. For instance, a Web Browser and a shell (or command prompt) are both processes. The operating system oversees all processes running on a computer and assigns each task a specific time slot to utilize the processor. 

Furthermore, the operating system assigns different resources and processes required, such as computer memory or drives. The operating system keeps a table called the process table to monitor the status of all processes. This table details each process with the resources it utilizes and its present condition.

What are the various stages of the process?

Processes can exist in three states: operating, ready, or waiting. When a process runs, it has all the necessary resources for execution and has been authorized by the operating system to utilize the CPU. Only a single process can be operating simultaneously. 

The remaining processes are either waiting for an external event, such as user input or disk access, or permission to use the CPU. In a genuine operating system, the waiting and ready states are represented as queues that contain the processes in those states.

Define Thread.  

A thread is a linear series of executions within a process. Threads are occasionally called lightweight processes because they possess specific process-like characteristics. Threads are commonly used to enhance application performance by utilizing parallelism. For instance, various tabs can function as separate threads in a browser. MS Word utilizes many threads, each assigned to text formatting and input processing tasks. 

What are the distinctions between process and thread?

A thread possesses its program counter (PC), a set of registers, and a place for its stack. Threads are not autonomous entities, unlike processes. Threads share their code area, data section, and OS resources with other threads, such as open files and signals.

What advantages can multithreaded programming offer? 

It enhances system responsiveness and facilitates resource sharing. It results in the implementation of a multiprocess architecture. It is more cost-effective and favored. 

Define Thrashing. 

Thrashing occurs when a computer's performance deteriorates or fails. Thrashing happens when a system dedicates more time to handling page defects than transactions. Dealing with page faults is essential to understanding the advantages of virtual memory, but thrashing harms the system. 

A higher page fault rate increases the paging device's workload in processing transactions. The line at the paging equipment grows, leading to longer service time for a page problem.

Define Buffer.

A buffer is a memory region temporarily holding data during transfer operations between devices or between a device and an application.

Define virtual memory.

Virtual memory deceives by giving the impression that every user possesses one or several continuous address spaces, all starting at address zero. Virtual address spaces typically have large sizes. Virtual memory utilizes disk space to expand the capacity of RAM. 

Running processes are indifferent to whether the memory is sourced from RAM or disk. Virtual memory is divided into smaller segments to create the appearance of a huge memory capacity, allowing pieces to be loaded into physical memory when needed by a process. 

Define the primary function of an operating system.

An operating system mediates between a computer user and the computer's hardware. An operating system aims to offer a convenient and efficient environment for users to run programs. 

An operating system is a software program that oversees and controls computer hardware. The hardware must have procedures in place to ensure the computer system's proper functioning and prevent user programs from disrupting the system's operation.

Define demand paging.

Demand paging loads a page into memory only when a failure occurs.

Define kernel.

The kernel is the core part of an operating system responsible for managing computer processes and hardware. It primarily oversees the functions related to memory and CPU time. It is an essential element of an operating system. The kernel is an intermediary connecting programs with data processing at the hardware level through inter-process communication and system calls.

Enumerate the various scheduling algorithms.

• First-Come, First-Served (FCFS) Scheduling. 
• Shortest-Job-Next (SJN) Scheduling. 
• Priority Scheduling. 
• Shortest Remaining Time. 
• Round Robin (RR) Scheduling. 
• Multi-level queue scheduling. 

Explain the purpose of multi-programming.

Multi-programming enhances CPU utilization by arranging jobs (code and data) to ensure the CPU is constantly busy executing a task. The primary goal of multi-programming is to maintain several jobs in the main memory simultaneously. When one job uses IO, the CPU might be allocated to other tasks. 

What is the time-sharing system?

Time-sharing is a natural progression of multiprogramming. The CPU executes numerous jobs through rapid switching, allowing users to engage with each program as it is executing. A time-shared operating system enables several users to share machines concurrently.

 

What issues arise in a computer system without an operating system?

• Inefficient allocation of resources
• Absence of User Interface Lack of File System
• Lack of networking
• Error handling is a significant concern.

Enumerate advantages of multithreaded programming.

A thread is commonly referred to as a lightweight process. The concept involves attaining parallelism by segmenting a process into several threads. Threads in the same process share memory space. 

FCFS stands for First Come, First-Served. It is a scheduling algorithm that processes tasks in the order they arrive.

FCFS is an acronym meaning First Come First Served. The FCFS scheduling method assigns jobs to the CPU based on their arrival order in the ready queue. FCFS is a non-preemptive scheduling mechanism where a process retains CPU control until it finishes execution or requests I/O. If a lengthier work is currently being processed by the CPU, shorter jobs that follow will experience delays.

What is the Round-Robin scheduling algorithm?

The round-robin scheduling technique evenly schedules processes by allocating each job a time slot or quantum. If a job is not completed within its quantum, it is interrupted, and the next job in line is executed, ensuring fair scheduling.

• Round-robin scheduling is inherently cyclic, which prevents hunger.
• Round-robin is a type of scheduling that follows a first-come, first-served approach.
• No process or task is given precedence or particular significance. RR scheduling is often referred to as time-slicing scheduling.

 List the various RAID levels.

A redundant array of independent disks is a group of many physical disk drives that the operating system perceives as a unified logical entity. It significantly reduced the disparity between rapidly advancing computers and sluggish disk drives. RAID encompasses various levels:

Level-0 Level-1 Level-2 Level-3 Level-4

Level 5 Level 6

What is the Banker's algorithm?

The banker's algorithm is a method for resource allocation and deadlock prevention. It ensures safety by simulating resource allocation up to the maximum possible amounts. Then, it performs a "s-state" check to assess potential activities before determining if further allocation is permissible.