Final answer:
A user-level thread is managed by the application, while a kernel-level thread is managed by the operating system. User-level threads are lighter-weight but limited in scalability, while kernel-level threads allow for true parallel execution on multiple processors.
Step-by-step explanation:
A user-level thread is a thread that is managed by the application, rather than the operating system. These threads are created and scheduled by the thread library provided by the programming language or application framework. Examples of user-level thread libraries include POSIX threads and Windows threads.
A kernel-level thread, on the other hand, is a thread that is managed by the operating system. These threads are created, scheduled, and managed by the operating system kernel. Examples of kernel-level thread implementations include Windows NT threads and Linux kernel threads.
The main difference between user-level threads and kernel-level threads is the level at which they are managed. User-level threads are lighter-weight and can be more efficient in terms of context switching, but they are limited in their ability to take advantage of multiprocessor systems.
Kernel-level threads, on the other hand, allow for true parallel execution on multiple processors, but they tend to be more heavyweight and have higher overhead due to the involvement of the operating system.