Which ONE of the following correctly gives the average turnaround time of the four processes in milliseconds?

We are given the following process information:

• $P1$: Arrival Time $(\text{AT}) = 0$, Burst Time $(\text{BT}) = 10$

• $P2$: $\text{AT} = 1$, $\text{BT} = 13$

• $P3$: $\text{AT} = 2$, $\text{BT} = 6$

• $P4$: $\text{AT} = 8$, $\text{BT} = 9$

Gantt Chart Execution (SRTF):

• At $t = 0$: $P1$ arrives with remaining time $10$. $P1$ runs from $t = 0$ to $t = 1$.

• At $t = 1$: $P2$ arrives with remaining time $13$. $P1$ has remaining time $9$. Since $9 < 13$, $P1$ continues to run until $t = 2$.

• At $t = 2$: $P3$ arrives with remaining time $6$. $P1$ has remaining time $8$. Since $6 < 8$, $P1$ is preempted and $P3$ starts executing.

• $P3$ runs from $t = 2$ to $t = 8$ (duration 6 ms) and completes execution at $t = 8$.

• At $t = 8$: $P4$ arrives with remaining time $9$. The processes in the ready queue are:

  • $P1$ with remaining time $8$

  • $P4$ with remaining time $9$

  • $P2$ with remaining time $13$

• The shortest remaining time is $P1$ ($8$ ms). $P1$ runs from $t = 8$ to $t = 16$ and completes execution at $t = 16$.

• At $t = 16$: Remaining processes are $P4$ ($9$ ms) and $P2$ ($13$ ms). $P4$ executes from $t = 16$ to $t = 25$ and completes at $t = 25$.

• At $t = 25$: $P2$ executes from $t = 25$ to $t = 38$ and completes at $t = 38$.

Completion Times (CT) and Turnaround Times (TAT = CT - AT):

• $P1$: $\text{CT} = 16 \implies \text{TAT} = 16 - 0 = 16$

• $P2$: $\text{CT} = 38 \implies \text{TAT} = 38 - 1 = 37$

• $P3$: $\text{CT} = 8 \implies \text{TAT} = 8 - 2 = 6$

• $P4$: $\text{CT} = 25 \implies \text{TAT} = 25 - 8 = 17$

Average Turnaround Time:

Thus, option D is correct.