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Table of contents
What is Multithreading in Operating System?
How does multithreading in OS work?
Applications of Multithreading in OS
Multithreading Models in Operating system 
Many-to-One Multithreading Model
One-to-One Multithreading Model
Many to Many Multithreading Model
Example of Multithreading in OS
Challenges of multithreading
Advantages of Multithreading Operating System
Disadvantages of Multithreading Operating System
Multithreading vs. multitasking vs. multiprocessing 
Frequently Asked Questions
What is single threading and multithreading in OS?
What is multithreading and its types in OS?
What is multithreading and multiprocessing in OS?
What are the different types of relationships between the multithreading models?
What is a thread and multithreading?
Last Updated: Apr 4, 2024

Multithreading Operating System

Author Ayushi Poddar
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Multithreading in operating systems is a concept that has revolutionized the way modern computing systems handle concurrent tasks and maximize resource utilization. As the demands for performance and responsiveness continue to rise, understanding multithreading is crucial for developers and system architects alike.

multithreading operating system

Multithreading requires a thorough comprehension of these two terms: process and thread. A method is a program that is being run. Threads are independent units that can be separated from a process.

Threads of Execution


Also Read, Multiprogramming vs Multitasking

What is Multithreading in Operating System?

A multithreading operating system is one that allows multiple threads to execute concurrently within a single process. This type of OS takes advantage of CPU cores with multiple threads, dividing process execution efficiently to increase the performance of multi-core processors. Each thread runs a part of a process's workload, making the overall execution faster and more efficient.

In such systems, context switching between threads is typically faster than between processes, as threads share the same memory space and resources, whereas processes do not. This sharing enables threads to communicate with each other more quickly than separate processes.

Multithreading is beneficial for tasks that can be divided into smaller, concurrent operations, and it's essential for modern applications that require real-time performance and high responsiveness. This operating system design is widely used in server and desktop applications, where it maximizes resource utilization and provides improved performance on multi-core CPUs.

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How does multithreading in OS work?

Multithreading in an operating system works by allowing multiple threads to exist within the context of a single process, sharing its resources but operating independently. Think of it like a team of chefs working in one kitchen; they share the same space and utensils (the process's resources), but each chef prepares a different dish simultaneously (the threads). The operating system manages these threads, scheduling them to run on the CPU in a way that maximizes efficiency—making sure that while one chef is waiting for the oven, another is chopping vegetables. This multitasking nature of threads can lead to faster execution of complex tasks, better resource utilization, and more responsive applications, especially on multi-core processors where threads can run truly concurrently. It's a clever juggling act that keeps the computer's operations smooth and efficient.

Applications of Multithreading in OS

Threads are utilized across various domains to enable multitasking and concurrency within applications. They are particularly useful in enhancing user experience in graphical interfaces, where background threads can process heavy tasks without freezing the UI. Servers employ threads to manage numerous network requests in parallel, ensuring efficient resource use and responsive client handling. Multimedia applications use threads for smooth playback and rendering, separating decoding and user interaction. Additionally, in scientific computing, threads parallelize complex calculations for faster results. Their lightweight nature and shared resources allow for high-performance applications that can do more in less time.

Also see, Components of Operating System

Multithreading Models in Operating system 

Multithreading models in operating systems define how threads are created, managed, and scheduled for execution. The primary models are the Many-to-One model, where many user-level threads are mapped to a single kernel thread; the One-to-One model, where each user-level thread corresponds to a kernel thread; and the Many-to-Many model, which allows many user-level threads to be mapped to many kernel threads. Some systems also implement a hybrid approach, combining aspects of the aforementioned models. These models balance the benefits of user-level thread flexibility and kernel-level thread robustness and efficiency, influencing the system's performance, scalability, and complexity of thread management. Each model has its trade-offs, affecting how effectively an OS can handle concurrent execution and utilize multi-core processors.

Many-to-One Multithreading Model

In the Many to One multithreading model, multiple user-level threads (also known as green threads or lightweight threads) are mapped to a single kernel-level thread. These user-level threads are managed by a runtime library or a thread library instead of the operating system. The kernel is unaware of the existence of user-level threads and treats the entire process as a single entity. This model allows for high concurrency at the application level but lacks true parallelism since only one thread can execute at a time due to the single kernel-level thread. Additionally, blocking system calls or thread blocking operations can cause all threads in the process to be blocked, leading to potential inefficiencies.

One-to-One Multithreading Model

The One to One multithreading model involves creating a separate kernel-level thread for each user-level thread. In this model, every user-level thread is managed directly by the operating system, providing true parallelism as multiple threads can execute simultaneously on multiple CPU cores if available. Each thread can perform blocking operations independently without affecting other threads. However, creating and managing kernel-level threads can incur additional overhead, especially in terms of system resources and context switching.

Many to Many Multithreading Model

The Many to Many multithreading model combines aspects of both the Many to One and One to One models. In this model, multiple user-level threads are mapped to an equal or smaller number of kernel-level threads, with the mapping dynamically adjusted based on the system's workload and resource availability. This model aims to achieve a balance between concurrency and parallelism by allowing multiple user-level threads to execute concurrently on fewer kernel-level threads. It offers flexibility and efficiency by allowing the operating system to schedule kernel-level threads while providing concurrency at the application level. However, managing the mapping between user-level and kernel-level threads adds complexity to the system.

Example of Multithreading in OS

An everyday example of multithreading in an operating system can be observed in a web browser. When you open your browser and have multiple tabs running, each tab can be seen as a separate thread. While you watch a video on one tab, another might be loading a webpage, and yet another could be running a plugin or extension, like a music player. These threads run simultaneously, ensuring that the video plays smoothly while your music streams without hiccups and web pages load seamlessly. Behind the scenes, the operating system is efficiently allocating CPU time and resources to each browser thread, making sure they all get a slice of the computational pie. This orchestration allows for a fluid, multitasked browsing experience without overwhelming the system or causing it to crash. It's like a digital symphony conductor, ensuring every section comes in at the right time to create a harmonious user experience.

Challenges of multithreading

Multithreading, while powerful, brings its own set of challenges. One of the primary issues is the complexity of managing concurrent threads, which can lead to race conditions where threads compete for resources, potentially causing inconsistent results. Deadlocks are another concern, where threads get stuck waiting for each other indefinitely. Ensuring thread safety involves intricate programming to manage shared data without stepping on each other's toes. There's also the overhead of context switching between threads, which, if not managed efficiently, can negate the performance benefits of multithreading. And let's not forget about debugging; tracing issues across multiple active threads can be like trying to solve a puzzle where the pieces keep moving. Balancing these threads to work harmoniously requires a deft hand and a keen understanding of the system's intricacies.

Advantages of Multithreading Operating System

Following are some of the advantages of the Multithreading Operating System :

  • Resource sharing: Because threads can share any process memory and resources, every program can perform several tasks inside the same address space.
  • Multiple Processor Architecture: Different threads can execute in parallel on many processors, allowing for high processor usage and efficiency.
  • Reduced Context Switching Time: As with Thread Context Switching, the threads reduce context switching time while keeping the virtual memory space the same.
  • Cost-effective: Allocating memory and resources throughout the process generation process has a cost. Context-switch threads are more affordable to construct since they can distribute process resources.

You can also read about layered structure of operating system.

Disadvantages of Multithreading Operating System

Following are some of the disadvantages of the Multithreading Operating System

  • Due to the fact that numerous user threads are routed to a single kernel thread. So, if one user thread makes a blocking system call, the kernel thread will be blocked, and all other threads will be blocked as well.
  • Multiple threads cannot run in parallel in a multiprocessor system because only one thread can reach the kernel thread at a time. Despite the fact that we have several processors, one kernel thread will only operate on one of them. As a result, the user thread will only run in the processor where the mapped kernel thread is active.
  • The kernel thread is assigned to many user threads. So, if one user thread makes a blocking system call, the kernel thread will be blocked, and all other threads will be blocked as well.
  • Multiple threads cannot run in parallel in a multiprocessor system because only one thread can access the kernel thread at any given moment. One kernel thread will execute on only one CPU, despite the fact that we have several processors. As a result, the user thread will execute in the same processor as the mapped kernel thread.

Must Read Threads in Operating System

Multithreading vs. multitasking vs. multiprocessing 





Basic ConceptUses multiple threads to perform different tasks within a single program.Involves executing multiple tasks or programs simultaneously.Uses multiple CPU cores to perform multiple computations concurrently.
GranularityFine-grained, as it operates within a single process.Coarse-grained, as it operates at the level of applications.Coarse-grained, operates at the process level, with each process running on its own CPU core.
Resource SharingThreads share the same memory space of the process they belong to.Each task has its own separate memory space.Each process operates in a separate memory space, but can share resources if programmed to do so.
Context SwitchingTypically faster and less resource-intensive because threads share the same memory context.Slower and more resource-intensive due to separate memory and application states.Context switching is significant as it involves switching between different CPU cores or processors.

Frequently Asked Questions

What is single threading and multithreading in OS?

Single threading in an OS handles one task at a time per process, leading to a simple but potentially slower execution. Multithreading allows a process to execute multiple threads concurrently, improving performance and efficiency, especially on multi-core systems.

What is multithreading and its types in OS?

There exist three established multithreading models classifying these relationships: Many to one multithreading model, One to one multithreading model, and Many to Many multithreading models.

What is multithreading and multiprocessing in OS?

Multithreading in an operating system allows a single process to run multiple threads concurrently for efficient resource use. Multiprocessing leverages multiple CPUs to run different processes in parallel, enhancing computational speed and multitasking capabilities.

What are the different types of relationships between the multithreading models?

The relationship can be established in one of three ways - The one-to-One model, the Many-to-One model, and the Many-to-Many model.

What is a thread and multithreading?

A thread is a unit of execution within a process, capable of performing tasks independently. Multithreading refers to the ability of an operating system to support multiple threads within a single process, allowing concurrent execution and efficient utilization of system resources.


Multithreading operating systems represent a sophisticated approach to concurrent processing, enabling a computer to perform multiple tasks simultaneously within a single program. By dividing processes into threads that can run in parallel, these systems maximize CPU utilization, reduce processing time, and improve the responsiveness of applications. This approach is pivotal in modern computing, where the demand for real-time processing and efficient resource management is ever-increasing. Multithreading not only bolsters the execution of complex tasks but also paves the way for more fluid multitasking experiences for the end-user, making it an essential feature in both consumer and enterprise computing environments.

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