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Introduction: Operating System Class Notes

Updated: Oct 16, 2022

Mobiprep has created last-minute notes for all topics of operating system to help you with the revision of concepts for your university examinations. So let’s get started with the lecture notes on Operating System (OS).

Our team has curated a list of the most important questions asked in universities such as DU, DTU, VIT, SRM, IP, Pune University, Manipal University, and many more. The questions are created from the previous year's question papers of colleges and universities.

Introduction of Operating System

Question- 1) Define Operating System.

Answer: An operating system is system software. It is an interface between the user and the hardware. It performs tasks like memory management, resource allocation, file management, process management, security, etc. It also controls the peripheral devices like printers and hard disks.


Question- 2) What are the main objectives of an operating system?

Answer: The objectives of an operating system are:

  1. Efficiency- The operating system must improve the efficiency of the system by the efficient allocation of resources.

  2. Convenience- The foremost objective of an operating system is to provide an easy-to-use interface for the users to communicate with the device.

  3. Evolution ability- An operating system must be capable of allowing new changes to be introduced without interfering with its performance.

  4. Resource management- The operating system should be able to keep track of the resources in a system. It should decide which process has to access the resource when multiple processes request for the same resource (priority assignment)

  5. Security- The operating system should be able to prevent any unauthorized access to the data and programs in the system.


Question- 3) Define the term buffering.

Answer: A buffer is an area in the main memory that stores temporary data. It is mainly used when the data is moved from one place to another. Buffering helps in increasing the performance of the system. It makes the CPU and the I/O devices work at the maximum possible speed without allowing them to be idle.


Question- 4) What is the drawback of batch processing OS?

Answer: The drawbacks of batch processing OS are:

  1. Job priority cannot be assigned

  2. Users cannot directly interact with the computer.

  3. The CPU utilization is very low. The CPU is idle most of the time because the speed of the I/O devices is slower than that of the CPU.


Question- 5) What is batch processing?

Answer: In batch processing, the user cannot interact directly with the computer. The jobs (or programs) in punch cards are submitted to an operator. The operator sorts the similar jobs into batches. The CPU can execute only one batch at a time. Here, the CPU is idle most of the time because the speed of the I/O devices is slower than that of the CPU.


Question- 6) What do you understand by Multi threading and multi tasking?



Simultaneous execution of multiple threads of a process (or an application) is called multi-threading. Multi-threading improves the performance of the operating system by making efficient use of the CPUs in a multi-processor system. Multi-threading involves the sub-division of various operations of a single process into separate threads that are executed simultaneously.


The simultaneous execution of many processes by the CPU is called multi-tasking. It improves CPU utilization. Multi-tasking is also called time-sharing. In multitasking, different tasks (or processes) are performed at the same time, while in multi-threading, multiple operations of a single process are performed at the same time.


Question- 7) Explain parallel systems.

Answer: Parallel systems have multiple processors running simultaneously in a computer system. Parallelism can be achieved in such systems. A process is sub-divided into many parts and each part is executed in parallel in separate processors. It decreases the execution time of the process. Thus, the efficiency of the computer can be increased.


Question- 8) What are the advantages of a distributed system?

Answer: The advantages of the distributed systems are:

  1. Malfunctioning of a single computer in a distributed system does not affect the other computers. Distributed systems are fault-tolerant.

  2. Resource sharing is easy in a distributed system.

  3. It provides better performance than the centralized systems.

  4. Distributed systems are scalable and flexible.

  5. Distributed systems have high computational power.


Question- 9) What are real time systems?

Answer: A system whose response must be guaranteed within the specified timing is called a real-time system. A real-time system must always meet the deadline. It is a time-bound system. It may be either time-sharing or event-driven.

Example: Air traffic control system.


Question- 10) What is the difference between batch processing and multiprogramming?


Batch Processing


  • Only one program can be executed at a time.

  • More than one program can be executed at a time.

  • The user cannot directly interact with the computer

  • The user can directly interact with the computer.

  • The CPU is idle most of the time.

  • ​The CPU is never idle.

  • CPU utilization is very low.

  • CPU utilization is high.

  • It is slow.

  • It is fast.


Question- 11) What is a program?

Answer: A program is a set of executable instructions that are written to perform a specific function. It is a passive entity. It is stored in secondary memory. A program which is being executed is called a process. A single program can create multiple processes when it is run many times.


Question- 12) Explain OS as a resource manager.

Answer: Resource management is one of the main functions of the operating system. The operating system allocates and deallocates the resources to the processes. If multiple processes request a single resource, the operating system allocates the resource to the processes according to their priority. i.e. the resource is first allocated to the process with the highest priority. Thus, the operating system plays the role of a resource allocator.

Time-sharing and space sharing are the two ways of sharing a resource. In time-sharing, a resource is allocated to a process for some time, and then it is allocated to some other process. In space sharing, the space of the resource is shared among the processes.


Question- 13) What is a kernel?

Answer: The kernel is the heart or core of the operating system. It is the part of the operating system which always resides in the main memory. It is an important and essential part of the operating system. All the privileged instructions are executed by the kernel. A code executed in kernel mode can access any memory location.

kernel in operating system


Question- 14) What is a Bootstrap Program?

Answer: The bootstrap program is the first program executed by the CPU when the computer is booted. It loads the operating system from the disk into the main memory and initializes it. After the bootstrap program is executed, the control is transferred to the initial address in the main memory and the operating system is executed.


Question- 15) What is an interrupt?

Answer: An interrupt is a signal that brings the activities of the CPU to a halt. The interrupts are generated by external I/O devices. The interrupts direct the CPU to execute the appropriate portion of the OS. Usually, an interrupt handler is run by the operating system whenever an interrupt occurs. The interrupt handler assigns priorities to the interrupts and handles them.

The interrupts are classified into two types: hardware interrupts and software interrupts. The hardware interrupts are generated by external I/O devices. The software interrupts are generated by a user program or by an application.


Question- 16)Explain the working of an operating system is event-driven.

Answer: The operating systems are event-driven because it always responds to the events assigned by the user. When the user executes a program, the operating system allocates memory and resources to that process. Since the operations of the operating system are based on the user applications and current events, the OS is considered as event-driven.


Question- 17) What is the difference between a hard real-time system and a soft real-time system?


Hard Real-Time System

​Soft Real-Time System

  • ​It can never miss the deadline.

  • ​Can occasionally miss the deadline.

  • Exceeding the time limit can cause serious consequences.

  • Exceeding the time limit does not have serious consequences.

  • The system becomes useless if it misses the deadline.

  • ​The system gradually becomes useless if it misses the deadline continuously.

  • Example:

ABS system in car, Air traffic control systems

  • Example:

Mp3 player, telephone switches etc.,


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