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Consider the following processes with time slice of 4 milliseconds (I/O requests are ignored) :

ProcessABCD
Arrival time0123
CPU cycle8495

The average turn around time of these processes will be

  • A.19.25 milliseconds
  • B.18.25 milliseconds
  • C.19.5 milliseconds
  • D.18.5 milliseconds

Answer: B

Round robin with a time slice of 4 ms gives the order A (0-4), B (4-8), C (8-12), D (12-16), A (16-20), C (20-24), D (24-25) and C (25-26). B finishes at 8, A at 20, D at 25 and C at 26.

\[ \text{turnaround} = \text{finish} - \text{arrival} \]

\[ A: 20,\; B: 7,\; C: 24,\; D: 22 \]

\[ \frac{20 + 7 + 24 + 22}{4} = 18.25 \text{ ms} \]

This is option (B). Options (A), (C) and (D) come from a different order of the queue or from using waiting time in place of turnaround time.

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