Operating System Interview Questions and Answers

An operating system (OS) is software that manages computer hardware and system resources and provides the tools that applications need to operate. The first OS was introduced in the early 1950s known as GMOs. An OS is responsible for managing, handling, and coordinating overall activities and sharing of computer resources Operating system is a crucial component of the system software in a computer system.

Here are the different types of operating systems

Batch Operating Systems: It is used when we can’t directly communicate with computer. In this each user prepare his program offline and submits them to computer operator.

Example: IBM’s MVS OS, Payroll etc.

Distributed Operating Systems: These Operating Systems are systems which model where distributed applications are running on multiple computers, linked by communications.

Example: AEGIS, AIX, Solaris, AMOEBA, Arachne, LOCUS, etc.

Time-sharing Operating Systems: A time-sharing operating system is a special type of multiprogramming operating system that is designed to accommodate many users and allows multiple computer programs to be run concurrently.

Example: UNIX, Linux, Multics, TOPOS-10 (DEC), etc.

Real Time Operating Systems (RTOS): RTOS is a software component that rapidly switches between tasks, giving the impression that multiple programs are being executed at the same time on a single processing core.

Example: PSOS, LynxOS, OSE, QNX, VRTX, RT Linux, air traffic control systems etc

Network Operating Systems: Network operating systems are installed on a server providing users with the capability to manage data, user groups and applications.

Example: UNIX, Linux, MacOS X, Novell NetWare, BSD etc.

Mobile Operating Systems: Mobile operating systems run exclusively on small devices such as smartphones, tablets and wearables.

Example: Android, iOS, Windows phone OS, and Symbian.

Microsoft Windows: It was Created by Microsoft. Microsoft Windows is one of the most popular and widely used operating systems for computers in the world.

Apple macOS: macOS is an operating system designed for the Apple Macintosh computer. It was developed by Apple. It is the second most widely used desktop OS, after Microsoft Windows.

Linux: Linux is Unix-like. It is an opensource and most used operating system.

Apple iOS: iOS is one of the most popular and widely used mobile operating system developed and created by Apple Inc.

Google Android: Google Android Operating System (OS) is Google’s Linux-based open-source operating system for mobile devices and Desktop systems. Android is the most popular operating system in the world, with over 2.5 billion+ active users spanning over 190 countries.

Kernel: It is an important part of the operating system. It is a system program that controls all programs running on the computer. The kernel is basically a bridge between the software and hardware of the system. It’s considered as a central component or module of OS.

Operating System: It is a system program that runs on the computer to provide an interface to the computer user so that they can easily operate on the computer.

Operating system can be further classified as Single and Multiprogramming batch system, Distributed operating system, Realtime operating system etc. On the other hand, a kernel is classified as monolithic kernels and microkernel.

Linux is a free and open-source operating system based on Unix standards. It was first released in September 1991 by Linus Torvalds. Windows is a commercial operating system whose source code is inaccessible. Windows Operating System was released by Microsoft in the year 1985.

Linux uses the monolithic kernel which consumes more running space whereas Windows uses the micro kernel which takes less space but system running efficiency is lower than Linux.

Linux provides high security than windows because Linux is open source.

Linux has three types of user account i.e., Regular, Root, and Service Account whereas in Windows there are four types of user account i.e., Administrator, Standard, Child, and Guest.

Android and iOS are operating systems primarily used in mobile technology, such as in tablet, smartphones, watches, iPad and more.

Android is an opensource and developed by Google. Its kernel type is Hybrid.

iOS is a closed with open-source elements and developed by Apple Inc.  Its kernel type is Linux-based.

• File Management
• Kernel
• Multi-Tasking
• Process Execution
• Interrupt
• Main memory Management
• Stored Management System
• Security Management
• Networking
• User Interface
• API

A race condition happens while more than one process is sharing the same code or resources. In this case, an unexpected result might occur as each process could access the shared variables at any time.

When a program is in process, and it does not get all the resources to execute, because other processes are using the same resources then this problem of not getting all needed resources is known as starvation.

The memory management of operating systems is responsible for allocating memory to processes, including converting logical addresses into physical addresses or swapping processes between internal and external memory.

In the multi-programming system, the system keeps different programs in different parts of the main memory simultaneously, and executes each of those concurrently.

In a multitasking system, programs are kept in the main memory so the system can execute them simultaneously.

Virtual memory is a section of volatile memory created temporarily on the storage drive. It is created when a computer is running many processes at once and RAM is running low. This is common while the memory cost of a software exceeds the space of a computer. The reason why this can be implemented is because of the virtual memory. It divides a program into several pieces and allows them to be temporarily stored in the external memory (disk) before the program needs it. By doing this, the program will regard itself to own a piece of continuous space.

Physical and virtual memory are forms of memory (internal storage of data). Physical memory exists on chips (RAM memory) and on storage devices such as hard disks. … Virtual memory is a process whereby data (e.g., programming code,) can be rapidly exchanged between physical memory storage locations and RAM memory.

Deadlock is a situation when more than two processes are waiting for the resource holding by each other, but no one is going to release first.

Paging is a computer memory management function that presents storage locations to the computer’s CPU as additional memory, called virtual memory.

There are cases when no pages are loaded into the memory initially, pages are only loaded when demanded by the process by generating page faults. This is called Pure Demand Paging.

There are the following objectives of Scheduling Algorithms:

• First-Come, First-Served (FCFS) Scheduling
• Shortest-Job-Next (SJN) Scheduling
• Shortest Remaining Time
• Round Robin (RR) Scheduling
• Priority Scheduling
• Multiple-Level Queues Scheduling

Process :

• A Process is a program in execution.      
• It requires more time for context switching.        
• The process is totally independent and doesn’t share memory.  
• Communication time is more.    
• It does not share data.
• It requires more resources.        

Thread:

• A Thread is the smallest unit of execution.
• As they are lighter than process it requires less time in context switching.
• Threads may share its memory with other threads.
• Communication time is less.
• It shares data with each other.
• It requires fewer resources.

PCB stands for Process Control Block, and it an operating system data structure, which can collect and store information about the processes. It is also known as the process descriptor. As soon as a process gets created, the OS creates a corresponding PCB to store the process status and information. With each transition, OS updates the PCB data structure.