Turn Around Time (TAT) in OS

What is Turn Around Time?

Turnaround time in OS refers to the total time taken for a process to complete its execution from the moment it enters the system until its termination. This includes the time spent waiting in various queues (such as the ready queue and I/O queues) and the actual time the process spends executing on the central processing unit.

In other words, turnaround time in OS measures the elapsed time between the submission of a process and the moment when it finishes its execution and produces the final output. Minimizing turnaround time is important for improving system efficiency and ensuring prompt responsiveness in a multitasking environment.

Formula

The formula for calculating the turnaround time of OS of a process in an operating system is:

$Turnaround Time = Completion Time - Arrival Time$

Where:

• Completion Time: The time at which the process completes its execution.
• Arrival Time: The time at which the process enters the system or is submitted for execution.

Example

Let's consider an example to illustrate the concept of turnaround time in OS:

Suppose we have three processes (P1, P2, and P3) that need to be executed on a CPU. Each process has an arrival time, burst time (execution time), and completion time. The turnaround time in OS for each process is calculated using the formula

$Turnaround Time = Completion Time - Arrival Time$

Here's the data for the three processes. Now let us calculate the turnaround time in OS:

Let's calculate the turnaround time for each process:

1. For P1:

   Turnaround Time = $15 - 0 = 15$ units

2. For P2:

   Turnaround Time = $11 - 2 = 9$ units

3. For P3:

   Turnaround Time = $19 - 4 = 15$ units

So, the turnaround times for the three processes are:

• P1: $15$ units

• P2: $9$ units

• P3: $15$ units

The average turnaround time for these processes can be calculated by adding up the individual turnaround times and dividing by the number of processes:

Average Turnaround Time = $(15 + 9 + 15) / 3 = 13$ units

Importance

The turnaround time in OS is an important performance metric in operating systems, and it holds significance for several reasons that we shall discuss now:

1. System Performance Evaluation:

   Turnaround time provides a comprehensive measure of the overall efficiency and responsiveness of the operating system.

2. User Experience:

   Shorter turnaround times lead to quicker response times for user requests and interactions. This is crucial for ensuring a responsive and interactive computing environment.

3. Resource Utilization:

   Turnaround time takes into account the time a process spends both waiting and executing. A lower turnaround time suggests that the system is effectively allocating resources and minimizing idle times, leading to better resource utilization.

4. Process Scheduling Evaluation:

   Operating systems employ various process scheduling algorithms to manage process execution.

5. Multitasking and Throughput:

   In a multitasking environment, where multiple processes compete for CPU time, turnaround time directly influences the overall throughput of the system.

Turnaround time is a versatile metric that reflects the overall efficiency, responsiveness, and resource utilization of an operating system.

What is Waiting Time?

After we have answered the question, what is the turnaround time in OS? let us now talk about waiting time.

Waiting time refers to the total amount of time that a process spends waiting in various queues before it gets access to the CPU for execution. Waiting time is a significant performance metric as it directly impacts the efficiency of resource utilization and overall system responsiveness.

In a multitasking environment**, multiple processes contend for the CPU's attention. When a process is in a "ready" state but not yet executing on the CPU, it is placed in a queue called the "ready queue." The waiting time for a process is the cumulative time it spends in the ready queue and any other queues, such as I/O queues, before it starts its execution.

Formula

The formula for calculating the waiting time of a process in an operating system depends on the scheduling algorithm and the specific characteristics of the processes and their execution. Generally, the waiting time of a process can be calculated using the formula:

$Waiting Time = Turnaround Time - Burst Time$

Where:

• Turnaround Time:

  The total time taken for a process to complete execution (arrival time to completion time).

• Burst Time:

  The time required for a process to complete its execution on the CPU.

Example

Let's consider an example to demonstrate the concept of waiting time in the context of process scheduling:

Suppose we have three processes (P1, P2, and P3) that need to be executed on a CPU. Each process has an arrival time, burst time (execution time), and completion time. We will calculate the waiting time for each process using the formula:

$Waiting Time = Turnaround Time - Burst Time$

Here's the data for the three processes:

Turnaround Time for each process can be calculated as:

$Turnaround Time = Completion Time - Arrival Time$.

Using this, we get:

1. For P1:

   Turnaround Time = $18 - 0 = 18$

   Waiting Time = $Turnaround Time - Burst Time$ = $18 - 8 = 10$

2. For P2:

   Turnaround Time = $12 - 1 = 11$

   Waiting Time = $Turnaround Time - Burst Time$ = $11 - 6 = 5$

3. For P3:

   Turnaround Time = $8 - 2 = 6$

   Waiting Time = $Turnaround Time - Burst Time$ = $6 - 4 = 2$

So, the waiting times for the three processes are:

• P1: $10$ units
• P2: $5$ units
• P3: $2$ units

Importance

Waiting time in the operating system is important for several reasons:

1. Resource Utilization:

   Longer waiting times indicate inefficient resource utilization, as processes are spending more time waiting for CPU time rather than executing.

2. System Responsiveness:

   Shorter waiting times lead to faster response times for user interactions and requests, contributing to a more responsive system.

3. Process Scheduling Evaluation:

   Waiting time helps evaluate the effectiveness of process scheduling algorithms. Efficient algorithms aim to minimize waiting times and optimize resource allocation.

4. Bottleneck Identification:

   Processes with consistently high waiting times can indicate potential bottlenecks or resource contention issues in the system.

5. Optimization:

   Monitoring and analyzing waiting times can guide system administrators in identifying areas for optimization, such as adjusting scheduling parameters or improving I/O handling.

Turn Around Time Vs Waiting Time

Let us now look at this table highlighting the differences between turnaround time in OS and waiting time in OS:

Completion Time in CPU Scheduling

Completion time in OS, in the context of CPU scheduling in operating systems, refers to the point in time when a process finishes its execution on the central processing unit (CPU). It marks the completion of the process's tasks and the generation of its final output.