GATE | GATE CS 2011 | Question 6

The time taken to switch between user and kernel modes of execution be t1 while the time taken to switch between two processes be t2.

Which of the following is TRUE?
(A) t1 > t2
(B) t1 = t2
(C) t1 < t2
(D) nothing can be said about the relation between t1 and t2


Answer: (C)

Explanation: Process switches or Context switches can occur in only kernel mode . So for process switches first we have to move from user to kernel mode . Then we have to save the PCB of the process from which we are taking off CPU and then we have to load PCB of the required process . At switching from kernel to user mode is done. But switching from user to kernel mode is a very fast operation(OS has to just change single bit at hardware level)

Thus T1< T2

This explanation has been contributed by Abhishek Kumar.

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