Difference between User level and Kernel level threads in Operating System

In this article, you will learn about the difference between the user and Kernel level threads. But before discussing the differences, you must know about the user and Kernel level threads and their advantages and disadvantages.

What is User Level Thread?

The User-level threads are small and faster as compared to kernel-level threads, and the OS directly supports user-level threads. Users implement the user-level threads, and the kernel is unaware of their existence and handles them as though they are single-threaded processes. These threads are represented by registers, the program counter (PC), stack, and some small process control. Furthermore, there is no kernel interaction in user-level thread synchronization.

It is also known as the many-to-one mapping thread, as the OS assigns every thread in a multithreaded program to an execution context. Every multithreaded process is treated as a single execution unit by the OS.

Advantages and Disadvantages of User Level Threads

There are various advantages and disadvantages of User-level Threads. Some of the advantages and disadvantages of User-level Threads are as follows:

Advantages

1. User level threads are simpler and faster to generate. They are also easier to manage.
2. Thread switching in user-level threads doesn't need kernel mode privileges.
3. These are more portable.
4. These threads may be run on any OS.

Disadvantages

1. The complete process is blocked if a user-level thread runs a blocking operation.
2. User-level threads don't support system-wide scheduling priorities.
3. It is not appropriate for a multiprocessor system.

What are Kernel Level Threads?

In Kernel Level Thread, the kernel handles all thread management. Every process doesn't have a thread table, but the kernel has one that maintains track of all of the threads in the system. If a thread wishes to make a new thread or stop an existing one, it initiates a kernel call that performs the work.

The kernel-level threads table contains each thread's registers, status, and other information. The data is identical to that of user-level threads, except it is now in kernel space rather than user space.

Advantages and Disadvantages of Kernel Level Threads

There are various advantages and disadvantages of kernel-level Threads. Some of the advantages and disadvantages of Kernel-level Threads are as follows:

Advantages

1. If a thread in the kernel is blocked, it does not block all other threads in the same process.
2. Several threads of the same process might be scheduled on different CPUs in kernel-level threading.
3. Kernel routines can be multithreaded as well.

Disadvantages

1. Compared to user-level threads, kernel-level threads take longer to create and maintain.
2. A mode switch to kernel mode is important to transfer control from one thread in a process to another.

Main differences between the User Level Threads and Kernel Level Threads

Here, you will learn the main differences between the User Level and Kernel Level Threads in the operating system. The operating system has various differences between the User Level and Kernel Level Threads are as follows:

1. Users implement the user-level threads. On the other hand, the OS implements kernel-level threads.
2. User-level threads may be created and handled much faster. In contrast, kernel-level threads take longer to create and maintain.
3. The entire process is halted if a single user-level thread carries out a blocking operation. On the other hand, if a kernel thread carries out a blocking operation, another thread may continue to run.
4. The user-level thread library includes the source code for thread creation, data transfer, thread destruction, message passing, and thread scheduling. On the other hand, the application code on kernel-level threads does not include thread management code. It is simply an API to the kernel mode.
5. User-level threads do not invoke system calls for scheduling. On the other hand, system calls are used to generate and manage threads at the kernel level.
6. The user-level thread is also referred to as the many-to-one mapping thread, as the OS assigns each thread in a multithreaded process to an execution context. On the other hand, One-to-one thread mapping is supported at the kernel level. Each user thread must be assigned to a kernel thread. This mapping is handled by the OS.
7. Context switch time is less in the user-level threads. On the other hand, context switch time is more in kernel-level threads.
8. User-level threads may operate on any OS. In contrast, kernel-level threads are specific to the OS.
9. Multithread applications are unable to employ multiprocessing in user-level threads. In contrast, Kernel-level threads may be multithreaded.
10. Some instances of user-level threads are Java threads and POSIX threads. On the other hand, some instances of Kernel-level threads are Windows and Solaris.

Head-to-head comparison between the User level threads and Kernel level threads

Here, you will learn the head-to-head comparison between the User Level and Kernel Level Threads in the operating system. The operating system has various differences between the User Level and Kernel Level Threads are as follows:

Conclusion

In summary, the primary distinction between User Level Threads and Kernel Level Threads is that the user maintains User Level Threads. In contrast, the kernel-level threads are handled by the OS. All modern OS supports the threading model, and the implementation of a thread will vary depending on the OS.