Operating System (OS) is the most essential software that runs on a computer. It acts as an interface between the user and the hardware. An OS performs various functions such as managing and coordinating system resources, executing and providing services for applications software, controlling and monitoring hardware devices, and providing security to the system. This article aims to explain the function of OS and focus on one of its types, the multi-programmed OS, in simple language.

The Function of Operating Systems

Resource Management

The OS manages system resources such as the central processing unit (CPU), memory, and input/output (I/O) devices. It allocates resources to different applications as per their requirements, prioritizing tasks according to their importance. This ensures that all programs receive an equal share of the resources, preventing any application from hogging resources and causing system failure.

Memory Management

The OS is responsible for managing the memory of the system. It allocates memory to different programs, ensuring that each program has enough space to operate without interfering with others. It also monitors the memory usage of each application, ensuring that they do not exceed their allocated space.

Device Management

The OS manages all the I/O devices of the system. It provides a standard interface for different hardware devices, making it easier for software applications to communicate with the devices. It also monitors the status of devices, ensuring that they are functioning correctly and resolving any conflicts that may arise.

User Interface

The OS provides an interface between the user and the computer hardware. It allows users to interact with the system using different modes of input such as keyboard, mouse, touchpad, or voice commands. The user interface is designed to be user-friendly and intuitive, making it easy for users to navigate and access different features of the system.


The OS provides security to the system by controlling access to different resources. It ensures that only authorized users have access to the system and its resources. It also provides features such as password protection, firewalls, and antivirus software, preventing unauthorized access and protecting the system from malware and other security threats.

Multi-Programmed Operating Systems

A multi-programmed OS is a type of operating system that allows multiple applications to run simultaneously on a computer. It enables efficient use of system resources by scheduling tasks in such a way that the CPU is always busy. This ensures that the system is being utilized to its full potential, minimizing idle time and maximizing the throughput.

Job Scheduling

In a multi-programmed OS, the OS schedules different jobs to run on the CPU. It selects the most suitable job from the job pool and assigns it to the CPU. This ensures that the CPU is always busy, even when one job is waiting for I/O operations to complete.

Time Sharing

A multi-programmed OS allows time-sharing, enabling multiple users to access the system simultaneously. Each user is provided with a separate terminal, and the OS switches between different user sessions, giving each user a time slice to interact with the system. This allows efficient use of system resources, enabling multiple users to work simultaneously on the same system.

Resource Sharing

A multi-programmed OS allows sharing of system resources between different applications. This ensures that all applications receive a fair share of system resources, preventing any application from hogging resources and causing system failure.

Fault Tolerance

A multi-programmed OS provides fault tolerance by isolating different applications from each other. This ensures that if one application fails, it does not affect other applications running on the system



(a) Write are the functions of operating systems? write a note on multi programmed operating systems ?

(b) Distinguish between client server and peer to peer model of distributed systems .


(a) With a Neat Sketch, Describe the services that an Operating System provides to users, processes and other systems.

(b) What is meant by Storage Structure? Discuss Storage Hierarchy.

(c) Write the Advantages and Disadvantages of using the same system call interface for manipulating both Files and Devices.


(a) What are the criteria for evaluating the CPU scheduling algorithms? Why do we need it?

(b) Define process. Explain various steps involved in change of a process state with process state neat transition diagram.


(a) What is synchronization? Explain how semaphores can be used to deal with n-process critical problem.

(b) Define a thread. Give the benefits of multithreading. What resources are used when a thread is created?


(a) How dose deadlock avoidance differ from deadlock prevention? Write about deadlock avoidance algorithm in detail.

(b) Different between external fragmentation and internal fragmentation. How to solve the fragmentation using paging?


(a) What is the purpose of paging the page table? Consider the following page reference string 1,2,3,4,5,1,2,3,4,5 for a memory with three frames. How many page faults would LRU and FIFO replacement algorithm?

(b) What are the disadvantages of single contiguous memory allocation? Explain.


(a) Briefly explain about single-level, two-level and three Structured directories.

(b) What is disk scheduling? Explain the C-SCAN scheduling by giving an example.


(a) Interrupt and spooling.

(b) UNIX file system.

(c) Program and system threats.

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