GATE | GATE-CS-2014-(Set-1) | Question 30

Which one of the following is FALSE?

(A) User level threads are not scheduled by the kernel.

(B) When a user level thread is blocked, all other threads of its process are blocked.
(C) Context switching between user level threads is faster than context switching between kernel level threads.
(D) Kernel level threads cannot share the code segment


Answer: (D)

Explanation:



User level thread Kernel level thread
User thread are implemented by user processes. 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.

Source: http://quiz.geeksforgeeks.org/operating-system-user-level-thread-vs-kernel-level-thread/

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