Scheduling criteria (turnaround time, waiting time, throughput) in Operating Systems - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the sentence to define turnaround time.

Operating Systems

Turnaround time is the total time taken from process submission to [1].

Drag options to blanks, or click blank then click option'

Aexecution

Barrival

Ccompletion

Dwaiting

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing turnaround time with waiting time.

Thinking it ends when the process starts execution.

Turnaround time measures how long a process takes from the moment it is submitted until it finishes completely.

2fill in blank

medium

Complete the sentence to define waiting time.

Operating Systems

Waiting time is the total time a process spends in the [1] queue before execution.

Drag options to blanks, or click blank then click option'

Aready

Bwaiting

Crunning

Dterminated

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing waiting time with execution time.

Confusing ready queue with waiting queue.

Waiting time counts how long a process waits in the ready queue before it gets CPU time.

3fill in blank

hard

Fix the error in the definition of throughput.

Operating Systems

Throughput is the number of processes completed per [1] unit of time.

Drag options to blanks, or click blank then click option'

Aprocess

BCPU

Cmemory

Dtime

Attempts:

3 left

💡 Hint

Common Mistakes

Using CPU or memory instead of time.

Confusing throughput with CPU utilization.

Throughput measures how many processes finish in a given time period.

4fill in blank

hard

Fill both blanks to complete the formula for turnaround time.

Operating Systems

Turnaround time = [1] time + [2] time

Drag options to blanks, or click blank then click option'

Awaiting

Bexecution

Carrival

Dcompletion

Attempts:

3 left

💡 Hint

Common Mistakes

Using arrival or completion time in the formula.

Mixing up waiting and arrival times.

Turnaround time is the sum of waiting time and execution (or burst) time.

5fill in blank

hard

Fill all three blanks to complete the throughput calculation example.

Operating Systems

If 10 processes complete in [1] seconds, throughput = [2] / [3]

Drag options to blanks, or click blank then click option'

A5

B10

Cseconds

D20

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping numerator and denominator.

Using wrong time value.

Throughput = number of processes / time = 10 / 5 = 2 processes per second.

Practice

1. Which scheduling criterion measures the total time taken from the arrival of a process to its completion?

easy

A. Turnaround time

B. Waiting time

C. Throughput

D. Response time

Solution

1. Step 1: Understand the definition of turnaround time

   Turnaround time is the total time from when a process arrives until it finishes execution.

2. Step 2: Compare with other criteria

   Waiting time is only the time a process waits before starting, throughput is number of processes completed per time, and response time is time until first response.

3. Final Answer:

   Turnaround time -> Option A

4. Quick Check:

   Turnaround time = total process duration [OK]

Hint: Turnaround = arrival to finish total time [OK]

Common Mistakes:

• Confusing waiting time with turnaround time
• Mixing throughput with time durations
• Thinking response time equals turnaround time

2. Which of the following correctly defines waiting time in process scheduling?

easy

A. Number of processes completed per unit time

B. Time from process arrival to completion

C. Time a process spends in the ready queue before execution

D. Time taken by CPU to execute the process

Solution

1. Step 1: Define waiting time

   Waiting time is the time a process spends waiting in the ready queue before it starts running on the CPU.

2. Step 2: Eliminate other options

   Time from process arrival to completion describes turnaround time, C describes throughput, and D is CPU burst time, not waiting time.

3. Final Answer:

   Time a process spends in the ready queue before execution -> Option C

4. Quick Check:

   Waiting time = time before execution [OK]

Hint: Waiting time = time before process runs [OK]

Common Mistakes:

• Confusing waiting time with turnaround time
• Thinking waiting time includes execution time
• Mixing throughput with waiting time

3. Consider three processes with the following completion times (in seconds): P1=10, P2=15, P3=20. If all arrived at time 0, what is the throughput if the total time observed is 20 seconds?

medium

A. 0.20 processes per second

B. 0.15 processes per second

C. 0.10 processes per second

D. 0.25 processes per second

Solution

1. Step 1: Calculate total processes completed

   All three processes (P1, P2, P3) completed within 20 seconds, so total completed = 3.

2. Step 2: Calculate throughput

   Throughput = number of processes completed / total time = 3 / 20 = 0.15 processes per second.

3. Final Answer:

   0.15 processes per second -> Option B

4. Quick Check:

   Throughput = 3/20 = 0.15 [OK]

Hint: Throughput = completed tasks ÷ total time [OK]

Common Mistakes:

• Dividing total time by number of processes instead of reverse
• Counting incomplete processes
• Using average completion time instead of total time

4. A scheduler reports the following for a process: Arrival time = 0, Start time = 5, Completion time = 12. The waiting time is incorrectly calculated as 7 seconds. What is the correct waiting time?

medium

A. 5 seconds

B. 7 seconds

C. 12 seconds

D. 0 seconds

Solution

1. Step 1: Understand waiting time formula

   Waiting time = Start time - Arrival time = 5 - 0 = 5 seconds.

2. Step 2: Identify error in reported waiting time

   The reported waiting time of 7 seconds is incorrect because it does not match the formula.

3. Final Answer:

   5 seconds -> Option A

4. Quick Check:

   Waiting time = start - arrival = 5 [OK]

Hint: Waiting time = start time minus arrival time [OK]

Common Mistakes:

• Using completion time instead of start time
• Adding instead of subtracting times
• Confusing waiting time with turnaround time

5. A system runs 4 processes with arrival times and burst times as follows:
P1: arrival=0, burst=4
P2: arrival=1, burst=3
P3: arrival=2, burst=1
P4: arrival=3, burst=3
If the scheduler uses First-Come-First-Serve (FCFS), what is the average turnaround time?

hard

A. 3.5 seconds

B. 4.5 seconds

C. 5.0 seconds

D. 6.0 seconds

Solution

1. Step 1: Calculate completion times using FCFS

   Process order by arrival: P1(0), P2(1), P3(2), P4(3).
   P1 completes at 0+4=4,
   P2 starts at 4, completes at 4+3=7,
   P3 starts at 7, completes at 7+1=8,
   P4 starts at 8, completes at 8+3=11.

2. Step 2: Calculate turnaround times

   Turnaround = completion - arrival:
   P1: 4-0=4,
   P2: 7-1=6,
   P3: 8-2=6,
   P4: 11-3=8.
   Average turnaround = (4+6+6+8)/4 = 24/4 = 6.0 seconds.

3. Final Answer:

   6.0 seconds -> Option D

4. Quick Check:

   Average turnaround = 24/4 = 6.0 [OK]

Hint: Turnaround = completion - arrival; average = sum/number [OK]

Common Mistakes:

• Calculating turnaround as burst time only
• Ignoring arrival times in scheduling order
• Mixing waiting time with turnaround time