What is Turnaround Time in CPU Scheduling?
When we use a computer or any electronic device, we want it to be fast and efficient. One of the factors that can affect the performance of the device is its CPU scheduling. The CPU, or central processing unit, is like the brain of the computer, and it allocates time for each task or program it needs to perform.
Turnaround time in CPU scheduling refers to the time it takes for a task to be completed from when it is submitted to when it is finished. In this article, we will discuss what turnaround time in CPU scheduling is, in great detail. But, before we dive deeper into the article, let’s first go through the list of topics listed under the table of contents (TOC) that we will cover in this article. Here’s the table:
Table of Contents (TOC)
- What is Turnaround Time in CPU Scheduling?
- What is Waiting Time in CPU Scheduling?
- Calculating Turnaround Time in CPU scheduling
- Difference Between Turnaround Time and Waiting Time (TAT vs WT)
- Key Differences Between Turnaround Time and Waiting Time (TAT vs WT)
What is Turnaround Time in CPU Scheduling?
Turnaround Time Definition: Turnaround Time or TAT is the time interval from the time of submission of a process to the time of the completion of the process.
Turnaround time is a significant factor in computer science that measures the time it takes for a task or program to complete after it’s been submitted. This metric helps determine the efficiency of the computer in handling various tasks. When a task is submitted, the CPU allocates it a specific time to execute, and the turnaround time is the duration it takes to complete the task.
Several factors can influence the turnaround time, including the complexity of the task, available resources, and the job’s priority level. For example, complex tasks requiring extensive computation time will take longer than simpler ones. Tasks with higher priority will also be completed more quickly than those with lower priority.
Understanding the turnaround time is crucial to enhancing the computer’s performance. By optimizing the CPU scheduling algorithm, we can minimize the turnaround time and increase the system’s speed and efficiency. This is particularly essential in real-time systems used in aerospace and defence, where delays can result in serious consequences.
In layman’s terms, we can say that the difference between CT (Completion Time) and AT (Arrival Time) is known as Turnaround Time in CPU scheduling.
Note: The TAT can also be calculated by adding the Burst Time (BT) and Waiting Time (WT).
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What is Waiting Time in CPU Scheduling?
Waiting Time Definition: Waiting Time or WT is the time a process spends in the ready queue waiting to be executed by the CPU.
High waiting times can cause delays in the execution of other processes, leading to lower system performance. Therefore, minimizing waiting time is crucial in optimizing the CPU scheduling algorithm. By reducing the waiting time, the CPU can execute more processes in less time, improving system efficiency.
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In layman’s terms, we can say that the difference between TAT and BT (Burst Time) is known as Waiting Time in CPU scheduling.
Note: Burst Time or BT is the total time a process requires for its overall execution.
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Calculating Turnaround Time in CPU Scheduling
In order to calculate the turnaround time of a process, you would need two things – Completion Time (CT) and ArrivealTime (Time). To understand how to calculate the turnaround time of a process, let’s go through an example.
Here’s an example:
Suppose they are four processes with burst Time, such as:
| Process | Burst Time |
|---|---|
| P1 | 4 |
| P2 | 6 |
| P3 | 8 |
| P4 | 10 |
Assuming that the arrival time of all the processes is 0 and the following scheduling algorithm is First-Come-First-Serve (FCFS).
- In order to calculate TAT for P1, we will add Burst Time to the Arrival Time = 4 + 0 = 4.
- Now, for the P2 process, the Waiting Time is 4. Hence, the TAT for P2 will be = 4 + 6 = 10.
- Now, for the P3 process, the Waiting Time is 10. Hence, the TAT for P2 will be = 10 + 8 = 18.
- Similarly, for the P3 process, the Waiting Time is 18. Hence, the TAT for P2 will be = 18 + 10 = 28.
- Therefore, the TAT for P1, P2, P3, and P4 is 4, 10, 18, and 28, respectively.
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Difference Between Turnaround Time and Waiting Time (TAT vs WT)
In order to undersatand the difference between TAT and WT in a better way, let’s explore it in a tabular format:
| Benchmark | Turnaround Time | Waiting Time |
|---|---|---|
| Definition | The time it takes for a process to complete from the moment it is submitted to the moment it is finished. | The total time a process spends waiting in a ready queue before reaching the CPU. |
| Calculation | Turnaround Time = Completion Time – Arrival Time/ Burst Time + Waiting Time | Waiting Time = Turnaround Time – Burst Time |
| Importance | Helps in understanding the efficiency of the CPU in processing tasks. | Can cause delays in the execution of other processes, leading to lower system performance. |
| Optimization | By optimizing the CPU scheduling algorithm, turnaround time can be reduced. | By minimizing the waiting time, more processes can be executed in less time, improving system efficiency. |
| Units | Usually measured in milliseconds, seconds or minutes. | Usually measured in the same unit as the burst time, such as milliseconds, seconds or minutes. |
| It is limited by the speed of the output device? | Yes. | No. |
Key Differences Between Turnaround Time and Waiting Time (TAT vs WT)
Here are the key differences between TAT and WT:
- The TAT is influenced by the speed of output devices such as printers or hard disks while waiting time is unaffected.
- The TAT formula is TAT = Burst time + Waiting time. The formula for waiting time is Waiting time = TAT – Burst time.
- Different CPU scheduling algorithms can produce different TATs for the same set of processes, but the algorithm does not affect the time a process executes or does I/O.
- TAT measures the total time a process takes from entering the ready queue to completion. Whereas waiting time only considers the time spent waiting in the ready queue and for I/O completion.
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Conclusion
In this article, we have explored what TAT in CPU scheduling is. We have also explored what WT is, the difference between TAT and WT, How to calculate TAT and various other topics in great detail.
Happy Learning!!
FAQs
What is turnaround time in CPU scheduling?
Turnaround time is the total time taken to execute a process from the moment it enters the CPU until it completes execution, including both CPU processing time and any time spent waiting in the ready queue or waiting for I/O operations. It is an important metric for evaluating the efficiency of CPU scheduling algorithms.
How is turnaround time calculated?
To calculate how long a process takes from start to finish (Turnaround time), you can use any of these formulas:
Turnaround Time = Completion Time - Arrival Time
Turnaround Time = Burst Time (BT) + Waiting Time (WT).
What is the significance of turnaround time in CPU scheduling?
Turnaround time is an important metric in CPU scheduling as it indicates how long a process takes to complete its execution. It helps in evaluating the efficiency and performance of a scheduling algorithm, and lower turnaround time is generally desirable.
How does CPU scheduling affect turnaround time?
The choice of CPU scheduling algorithm can significantly impact the turnaround time. Different algorithms prioritize processes differently, leading to variations in the time taken for process completion. Efficient scheduling algorithms aim to minimize the turnaround time.
Can a process have a negative turnaround time?
No, a process cannot have a negative turnaround time. Turnaround time is always a positive value since it represents the time taken for a process to complete execution.
What factors affect turnaround time?
Turnaround time can be affected by several factors, such as the scheduling algorithm used, the number of processes in the queue, and the priority of each process. Apart from these, system load and resource availability can also impact turnaround time.
What are the types of CPU scheduling algorithms?
There are several types of CPU scheduling algorithms, such as First-Come, First-Served (FCFS), Shortest Job Next (SJN), Round Robin (RR), and Priority Scheduling. Each algorithm has its advantages and disadvantages, and hence, the turnaround time is affected differently.
Can turnaround time be minimized?
Turnaround time can be minimized by optimizing scheduling algorithms and managing process priorities effectively. Implementing efficient resource management and reducing context switching can also help in decreasing turnaround time.
What is the relationship between turnaround time and waiting time?
Turnaround time and waiting time are closely related. While turnaround time includes waiting time, execution time, and other delays, waiting time refers to the time a process spends waiting in the queue. Reducing waiting time directly impacts turnaround time positively.
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