An OS contains 10 identical processes that were initiated at the same time.Each process contains 15 identical requests. Each request consume 20 msec of CPU time.A request is followed by an I/O operation which consumes 10 msec.The CPU scheduling overhead is 2 msec. The system uses Round Robin scheduling with the time quantum of 10 msec.
Q1) What is the response time of 1st request of last process ? A) 210 msec B) 140 msec c) 230 msec D) 240 msec
Q2) The subsequent request of the processes receives a response times of A) 110 msec B) 220 msec C) 230 msec D) 240 msec
Ans: Q1) D
What I thought :
For 1 process, there are 15 request so 15 * ( 20 + 10) = 450 msec But all answers are so small than this approach. So no need to think about further i.e. CPU overhead then 2nd...3rd...processes.
Here my problem is I didn't get the concept behind this question properly. CPU overhead ( i.e context switching ) will take place between 10 processes or each process's 15 request. So please tell how this scenario will work.
I didn't get the meaning of 2nd question.