Question

Given Data:
- Two processors: \( M_1 \) and \( M_2 \)
- Four processes: \( P_1, P_2, P_3, P_4 \)
- CPU bursts: \( P_1 = 20 \), \( P_2 = 16 \), \( P_3 = 25 \), \( P_4 = 10 \)
- Priority order for \( M_1 \): \( P_1 > P_3 > P_2 > P_4 \)
- Priority order for \( M_2 \): \( P_2 > P_3 > P_4 > P_1 \)
- Scheduling: Non-preemptive priority scheduling

Step 1: Assigning Processes to Processors
At \( t = 0 \), both processors are free. The highest-priority process for each processor is scheduled:
- \( M_1 \) gets \( P_1 \) (highest priority on \( M_1 \), burst = 20 ms).
- \( M_2 \) gets \( P_2 \) (highest priority on \( M_2 \), burst = 16 ms).

Step 2: Scheduling Remaining Processes
- \( P_2 \) finishes at \( t = 16 \), so \( M_2 \) picks the next highest-priority process, \( P_3 \) (burst = 25 ms).
- \( P_1 \) finishes at \( t = 20 \), so \( M_1 \) picks \( P_4 \) (burst = 10 ms).
- \( P_4 \) finishes at \( t = 30 \), and \( P_3 \) finishes at \( t = 41 \).

Step 3: Calculate Waiting Times
- \( P_1 \) starts at 0, so waiting time = \( 0 \) ms.
- \( P_2 \) starts at 0, so waiting time = \( 0 \) ms.
- \( P_3 \) starts at 16, so waiting time = \( 16 \) ms.
- \( P_4 \) starts at 20, so waiting time = \( 20 \) ms.

Step 4: Compute Average Waiting Time
\[ \text{Average waiting time} = \frac{(0 + 0 + 16 + 20)}{4} = \frac{36}{4} = 9 \text{ ms}. \]

Final Answer: The average waiting time of the processes is \( 9 \) milliseconds.

• A. 9.00
• B. 8.75
• C. 6.50
• D. 7.50

Hint:

In priority scheduling, the waiting time depends on the order in which processes are executed. The waiting time for each process is the total time it waits for other higher-priority processes to finish.

Answer 1

The Correct Option is A

Step 1: Initial Setup and Process Priorities
- Processor \( M_1 \) priority order: \( P_1 > P_3 > P_2 > P_4 \).
- Processor \( M_2 \) priority order: \( P_2 > P_3 > P_4 > P_1 \).
- CPU burst times:
\( P_1 = 20 \) ms, \( P_2 = 16 \) ms, \( P_3 = 25 \) ms, \( P_4 = 10 \) ms.

Step 2: Process Scheduling
- \( M_1 \) schedules \( P_1 \) first (highest priority), running for 20 ms.
- \( M_2 \) schedules \( P_2 \) first (highest priority), running for 16 ms.
- Remaining processes: \( P_3 \) (25 ms), \( P_4 \) (10 ms).
- \( M_1 \) next schedules \( P_3 \) (second priority), running for 25 ms.
- \( M_2 \) next schedules \( P_4 \) (second priority), running for 10 ms.

Step 3: Calculating Waiting Times
- \( P_1 \): Starts at \( t=0 \), waiting time = 0 ms.
- \( P_2 \): Starts at \( t=0 \), waiting time = 0 ms.
- \( P_3 \): Starts after \( P_2 \) finishes, at \( t=16 \), so waiting time = 16 ms.
- \( P_4 \): Starts after \( P_1 \) finishes, at \( t=20 \), so waiting time = 20 ms.

Step 4: Calculating Average Waiting Time
Total waiting time = \( 0 + 0 + 16 + 20 = 36 \) ms.
Average waiting time = \( \frac{36}{4} = 9 \) ms.

Final Answer: The average waiting time is 9 milliseconds.