Operating System | User Level thread Vs Kernel Level thread

User level thread Kernel level thread
User thread are implemented by users. kernel threads are implemented by OS.
OS doesn’t recognized user level threads. Kernel threads are recognized by OS.
Implementation of User threads is easy. Implementation of Kernel thread is complicated.
Context switch time is less. Context switch time is more.
Context switch requires no hardware support. Hardware support is needed.
If one user level thread perform blocking operation then entire process will be blocked. If one kernel thread perform blocking operation then another thread can continue execution.
Example : Java thread, POSIX threads. Example : Window Solaris.

Below is the Previous Year Gate Question
http://quiz.geeksforgeeks.org/gate-gate-cs-2007-question-17/

References:

http://www.cs.iit.edu/~cs561/cs450/ChilkuriDineshThreads/dinesh%27s%20files/User%20and%20Kernel%20Level%20Threads.html

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