Difference between user-level and kernel-supported threads?

Question

I've been looking through a few notes based on this topic, and although I have an understanding of threads in general, I'm not really to sure about the _differences between user-level and kernel-level threads_.I know that processes are basically made up of multiple threads or a single thread, but are these thread of the two prior mentioned types?From what I understand, kernel-supported threads have access to the kernel for system calls and other uses not available to user-level threads.So, are user-level threads simply threads created by the programmer when then utilise kernel-supported threads to perform operations that couldn't be normally performed due to its state?

Answer 1

In order to create threads one has to ask the operating system through system calls. What is being done with the created threads implies if they are user-level or kernel-level.

With kernel level threads, they are just being created to execute a piece of code and each time a new task is available, a new thread is created through the system calls.

On the other hand, user level threads are just created once using system calls, and they are kept alive so that each time a task becomes available for execution, it can do so immediately.