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Operating System

Chapter 1: Introduction to Operating System 

— Definition of Operating System.

— Evolution of operating systems – simple batch systems, multi-programmed batch systems, time sharing systems.

— Functions of an operating system

— Characteristics of Operating System

— Single user and multi-user operating systems

Open-source and closed-source operating systems.

Important Questions with their Answers of “Introduction to operating system”

— MCQs and Fill in Blanks

— Short term Questions

— Long Term Questions


Chapter 2: Process Overview

Definition of process, process states, process life cycle,

Process Control Block (PCB),

Process Scheduling – Scheduling queues,

Schedulers (short term, medium term and long term).

Dispatcher.

Context Switch.

Important Questions with their Answers of “Process Overview”

— MCQs and Fill in blanks

Short term Questions

Long Term Questions


Chapter 3: CPU Scheduling

  • CPU Scheduler,
  • Preemptive and non-preemptive scheduling.
  • Scheduling criteria – CPU utilization, Throughput, Turnaround time, Waiting time, Response time.
  • Scheduling Algorithms: First-Come-First-Serve, Shortest-Job-First, Priority Scheduling, Round-Robin.

Important Questions with their Answers of “CPU Scheduling”

  • MCQs and Fill in blanks
  • Short term Questions
  • Long Term Questions

Long Term Questions of “Introduction to operating system”

Qus 1: What is Operating System? Also, explains the evolution of Operating System ?

Qus 2: What is Operating System? Also, explains the Functions of Operating System ?

Qus 3: What is Single-User Operating System and Multi-User Operating System? Also, explain the difference between these two?

Qus 4: What is Open-Source Operating System and Closed-Source Operating System? Also, explain the difference between these two?


Qus 1: What is Operating System? Also, explains the evolution of Operating System ?

Ans: Operating System is the system software which provides the interface between the users application and the computer hardware and controls and manages the overall resources of computer.

Evolution of Operating System:

Operating System have gone through a long history of evolution. The various evolution of operating system are given below:

  • System Batch System
  • Multi-programming Batch System
  • Time Sharing System
  • Personal System
  • Parallel System
  • Distributed System
  • Real Time System

System Batch System

The first computers used batch operating systems, in which the computer ran batches of jobs without stop. Programs were punched into cards that were usually copied to tape for processing. When the computer finished one job, it would immediately start the next one on the tape.

  • In this type of system, there is no direct communication between the user and the computer.
  • The user must present the job (written on card or tape) to the computer operator.
  • Then the computer operator holds a batch of multiple jobs on an input device.
  • Jobs are put together according to language and requirement.
  • Then a special program, monitor, manages the execution of each program in the batch.
  • Monitor is always in main memory and available for execution.

Disadvantages of Simple Batch System

  • Lack of interaction between the user and the job.
  • CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU.
  • Difficult to provide the desired priority.

Multi-programming Batch System

  • In Multi-programming Batch System, the operating system picks up and begins to execute one of the jobs from memory.
  • Once this job requires an I/O operation operating system switches to another job (CPU and OS always busy).
  • Jobs in the memory are always less than the number of jobs on disk.
  • If many jobs are ready to run at the same time, then the system chooses which one to run through the process of CPU Scheduling.
  • In Non-multiprogramming system, there are moments when CPU sits idle and does not do any work.
  • In Multiprogramming system, CPU will never be idle/inactive and keeps on processing.

Advantages of Multi-programming System

  • High and efficient CPU utilization.
  • User feels that many programs are allotted CPU almost simultaneously.

Disadvantages of Multi-programming System

  • CPU scheduling is required.
  • To accommodate many jobs in memory, memory management is required.

Time Sharing Systems

Time sharing Systems are very similar to Multi-programming batch systems. In fact time sharing systems are an extension of multi-programming systems.

The main difference between Multi-programmed Batch Systems and Time-Sharing Systems is that in case of Multi-programmed batch systems, the objective is to maximize processor use, whereas in Time-Sharing Systems, the objective is to minimize response time.

Advantages of Time Sharing systems:

  • Provides the advantage of quick response.
  • Avoids duplication of software.
  • Reduces CPU idle time.

Disadvantages of Time Sharing systems:

  • Problem of reliability.
  • Question of security and integrity of user programs and data.
  • Problem of data communication.

Personal Systems

Earlier, CPUs and PCs lacked the features needed to protect an operating system from user programs. PC operating systems therefore were neither multiuser nor multitasking. However, the goals of these operating systems have changed with time; instead of maximizing CPU and peripheral utilization, the systems opt for maximizing user convenience and responsiveness. These systems are called Desktop Systems and include PCs running Microsoft Windows and the Apple Macintosh.

Parallel Systems

Parallel operating systems are designed to make efficient use of computers with multiple processors, and many operating systems currently on the market can take full advantage of multiple processors if present, providing the application programs they are running have been written using a programming language that supports multi-threading.

The general idea is that different threads of the program can be executed simultaneously, speeding up the execution of the program as a whole. Programs written for single-processor computers can often run on a multi-processor system, but can only execute on one processor at a time.

Distributed System

A distributed system is one in which various user resources reside in separate computer systems connected by a network. The computer systems involved may have diverse hardware and software platforms, but the user is presented with a uniform computing environment thanks to a distributed system architecture that provides a standard communications interface. This intermediate layer of software hides the complexity created by the intercommunication of such diverse technologies.

Advantages Distributed System:

  • With resource sharing facility, a user at one site may be able to use the resources available at another.
  • Speedup the exchange of data with one another via electronic mail.
  • If one site fails in a distributed system, the remaining sites can potentially continue operating.
  • Better service to the customers.
  • Reduction of the load on the host computer.
  • Reduction of delays in data processing.

Types of Distributed Systems:

Following are the two types of distributed operating systems used:

  1. Client-Server Systems
  2. Peer-to-Peer Systems

Real Time System

A  real-time system is defined as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment. The time taken by the system to respond to an input and display of required updated information is termed as the response time. So in this method, the response time is very less as compared to online processing.

Real-time systems are usually dedicated, embedded systems. An operating system does the following activities related to real-time system activity.

  • In such systems, Operating Systems typically read from and react to sensor data.
  • The Operating system must guarantee response to events within fixed periods of time to ensure correct performance.

Types of Real-Time Systems:

  1. Hard real-time systems
  2. Soft real-time systems

Qus 2: What is Operating System? Also, explains the Functions of Operating System ?

Ans: Operating System(OS) is the system software which manages user applications and their interaction with the computer hardware. An operating system is software that allows a user to run other applications on a computing device.

Function of Operating System: 

The various function of Operating System are as given below:

  1. Memory Management.
  2. Processor Management.
  3. Device Management.
  4. File Management.
  5. Secondary Storage Management.
  6. Security and Protection.
  7. Network Management.
  8. Control Over Performance.
  9. Error-Detecting.
  10. Coordination between other software and users

  1. Memory Management:
  • The operating system manages and keep track the Primary Memory or Main Memory.
  • Allocates the memory to a process when requests by it.
  • De-allocates the memory when a process has been terminated or it is performing I/O operation.
  • In multi-programming, it decides which process will get memory when and how much.
  1. Processor Management:
  • Keep tracks of processor and status of process. Program that does this is called traffic controller.
  • In multi-programming it decides which process get the processor when and how much time. This function is called process scheduling.
  • Allocate the processor (CPU) to a process.
  • De-allocate processor when processor is no longer required.
  1. Device Management:
  • It keeps track of all the peripherals devices.
  • It decides which process gets the device when and for how much time.
  • Allocates the device in the effective and efficient way.
  • De-allocates devices when not required.
  1. File Management:
  • It keeps track of information, location, uses, status and many more. The collective facilities are known as file system.
  • Decides who gets the resources and for how much long time.
  • Allocates the resources and de-allocates them when required.
  1. Secondary Storage Management:
  • Main memory as a limited size and it is volatile i.e. it loses its contents as soon as power turns off. The operating system performs following function in regard to secondary storage management.
  • Scheduling the requests for memory access i.e. Disk scheduling.
  • Creation and deletion of files.
  1. Security and Protection:
  • It provide password protection to user data, operating system prevents unauthorized access to programs and data of user.
  • It provides the security by encryption and decryption.
  1. Network Management:
  • An operating system works as a network resource manger when multiple computers are in a network.
  1. Control Over Performance:
  • Recording delays between request for a service and response from the system.
  1. Error-Detecting:
  • It detects production of dumps, traces, error messages and other debugging and error-detecting aids.
  • Operating system constantly monitor the system for detecting the error to avoid malfunctioning of computer system.
  1. Coordination between other resource and user:
  • Operating system also perform coordination and assignment of compilers, interpreters, assemblers and other software to the various users of the computer systems.

Qus 3: What is Single-User Operating System and Multi-User Operating System? Also, explain the difference between these two?

Ans: Single-User Operating System is a system in which only one user can access the computer system at a time.

Multi-User Operating System is a system that allows more than one user to access a computer system at one time.

The difference between single user operating system and multi user operating system are given below:

Characteristics  Single-User Operating System  Multi-User Operating System
Definition A Single-User Operating System is a system in which only one user can access the computer system at a time. A Multi-User Operating System is a system that allows more than one user to access a computer system at one time.
Super User  A super user gets all the powers of maintaining the system and making changes to ensure the system runs smoothly. Super user does not exist when it comes to a multi-user operating system as each entity has control over their working.
 Complexity  Single-User Operating System is simple.  Multi-User Operating System is complex.
Performance  Only one task at one time gets performed.   Schedules different tasks for performance at any rate
Example  Windows, Apple Mac OS  UNIX, Linux and Mainframes

Qus 4: What is Open-Source Operating System and Closed-Source Operating System? Also, explain the difference between these two?

Ans: Open Source Operating Software is distributed under a licensing agreement which allows computer code to be shared, viewed and modified by other users and organizations.

Closed Source Operating System use code that is proprietary and kept secret to prevent its use by other entities.

The difference between Open-Source Operating System and Closed-Source Operating System are given below:

Characteristics  Open-Source Operating System  Closed-Source Operating System
Cost  It is a free of cost software  It is a paid software.
Security  The code of open source operating software can be viewed, shared and modified by community, which means anyone can fix, upgrade and test the broken code. However, because of availability, the source code is open for hackers to practice on.  Closed source software can be fixed only by a vendor. If something goes wrong with the software, you send a request and wait for the answer from the support team.
Usability  User guides are not required by law and are therefore often ignored. When manuals are written, they are often filled with jargon that is difficult to follow.  Usability is a high selling point due to expert usability testing for a more targeted audience. User manuals are also provided for immediate reference and quick training, while support services help to maximize use of the software.
Source Code Availability  Open source operating software provides an ability to change the source code without any restrictions. Individual users can develop what they want and get benefits from innovation developed by others within the user community. Сlosed source operating software is more restricted than open source software because the source code cannot be changed or viewed. However, such limitation is what may contribute to CSS security and reliability.
Quality of Supports Open source software relies on a loyal and engaged online user community to deliver support via forums and blogs, but this support often fails to deliver the high level of response that many consumers expect Service and support are probably the greatest advantages of using closed source. Ongoing support is a key selling point for users with little technical skills and one of the main reasons people choose closed source over open source software.

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‘Operating System’ Practical

  1. To install and configure MS Windows 7/8/10 on a computer
  2. To get familiar with general Windows commands – ECHO, CLS, DIR, TREE, MD, CD, TYPE, RD, DEL, MOVE, COPY , REN, ATTRIB, COLOR, DATE, TIME, ERASE, FIND, FC, MORE, CMD, PATH, SYSTEMINFO, SHUTDOWN, TASKLIST, TASKKILL, VER, VOL, CHKDSK
  3. To use wildcard characters for copying, moving, renaming, and deleting files and directories in a given hierarchical directory structure under Windows’s command prompt.
  4. To get familiar with windows control panel components.
  5. To use Windows backup and restore features.
  6. To get familiar with commonly used Windows PowerShell cmdlets like Get-ChildItem, GetContent, Get-Command, Get-Help, Clear-Host, Copy-Item, Move-Item, Remove-Item, Rename-Item, Get-Location, Set-Location, Write-Output, Get-Process, Stop-Process.
  7. To write scripts in Windows PowerShell to automate tasks.