🏷️Difference between User Level thread and Kernel Level thread

📌User-Level Thread

• The User-level Threads are implemented by the user-level software.
• The User-level threads are basically created and implemented by the thread library which OS provides as an API for creating the managing synchronizing threads.
  • It is faster than the kernel-level threads, it is basically represented by the program counter, stack, register, and PCB.
• ex) POSIX threads
• These are managed entirely by the user-level libraries, rather than the operating system.
• They are invisible to the OS, which sees only a single process regardless of the number of threads within that process.

📌Kernel-Level Thread

• In terms of the Operating systems basically, the threads are the unit of execution within a process.
• The kernel level threads are also kinds of threads which is directly handled via kernel threads management.
• The Kernel-level threads are directly handled by the OS directly whereas the thread’s management is done by the kernel.
• In the Kernel Level Threads, Each thread is self-organizing and the kernel provides each thread with its own context with information about the thread’s status, such as its name, group, and priority.
• ex) POSIX threads, Java threads, Mach C-Threads
  • Mach [mʌk]: Macintosh's Kernel
• The OS is fully aware of the existence of these threads.

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Parameters	User Level Thread	Kernel Level Thread
Implemented by	by users	by Operating System
Recognize	OS doesn’t recognize user-level threads.	Kernel threads are recognized by Operating System.
Implementation	easy.	complicated.
Context switch time	Context switch time is less.	Context switch time is more.
Hardware support	Context switch requires no hardware support.	Hardware support is needed.
Blocking operation	If one user-level thread performs a blocking operation then the entire process will be blocked.	If one kernel thread performs a blocking operation then another thread can continue execution.
Multithreading	Multithread applications cannot take advantage of multiprocessing.	Kernels can be multithreaded.
Creation and Management	User-level threads can be created and managed more quickly.	Kernel-level level threads take more time to create and manage.
Operating System	Any operating system can support user-level threads.	Kernel-level threads are operating system-specific.
Thread Management	The thread library contains the code for thread creation, message passing, thread scheduling, data transfer, and thread destroying	The application code does not contain thread management code. It is merely an API to the kernel mode. The Windows operating system makes use of this feature.
Example	Java thread, POSIX threads.	Window Solaris.
Advantages	User Level Threads are simple and quick to create. Can run on any operating system They perform better than kernel threads since they don’t need to make system calls to create threads. In user-level threads, switching between threads does not need kernel mode privileges.	Scheduling multiple threads that belong to the same process on different processors is possible in kernel-level threads. Multithreading can be there for kernel routines. When a thread at the kernel level is halted, the kernel can schedule another thread for the same process.
Disadvantages	Multithreaded applications on user-level threads cannot benefit from multiprocessing. If a single user-level thread performs a blocking operation, the entire process is halted.	Transferring control within a process from one thread to another necessitates a mode switch to kernel mode. Kernel-level threads take more time to create and manage than user-level threads.
Memory management	In user-level threads, each thread has its own stack, but they share the same address space.	In kernel-level threads have their own stacks and their own separate address spaces, so they are better isolated from each other.
Fault tolerance	User-level threads are less fault-tolerant than kernel-level threads. If a user-level thread crashes, it can bring down the entire process.	Kernel-level threads can be managed independently, so if one thread crashes, it doesn’t necessarily affect the others.
Resource utilization	User-level threads don’t take full advantage of the system resources, As they don’t have direct access to the system-level features like I/O operations	It can access to the system-level features like I/O operations.So it can take full Advantages of System Resources.
Portability	User-level threads are more portable than kernel-level threads.	Kernel-level threads are less portable than User-level threads

📌References

• Difference between User Level thread and Kernel Level thread