# Important terms used in process scheduling

This article will cover all those terms which you will come across while studying various process scheduling algorithms. In this article, we will define all those terms which you must know before studying any of the process scheduling algorithms. We will describe each of them in brief.
Submitted by Monika Sharma, on June 24, 2019

1) Arrival Time (AT)

The time when the process arrives into the running state is called as the Arrival time of the process. In simple words, the time at which any process enter the CPU is known as the arrival time.

2) Completion Time (CT)

The time when the Process is done with all its execution and it enters the termination state is called as the completion time of the process. It can be also defined as the time when a process ends.

3) Burst Time (BT)

The time for which the process needs to be in the running state is known as the burst time of the process. We can also define it as the time which a process requires for execution is the Burst time of the process.

4) Turn Around Time (TAT)

Turn Around time can be defined as the total time the process remains in the main memory of the system. The Ready state, Waiting for state and the Running State, together make up the main memory of the system. So, the time for which the process remains in these states is known as the Turn Around Time of the process. In simple words, it is the time that a process spends after entering the ready state and before entering the termination state.

It can be calculated as follows:

```    Turn Around Time = Completion Time – Arrival Time
TAT = CT - AT
```

5) Waiting Time (WT)

The time for which a process waits for going into the running state. It is the sum of the time spent by the process in the ready state and the waiting state. Another way of calculating it is as follows:

```    Waiting Time= Turn Around Time – Burst Time
WT = TAT – BT
```

6) Response Time

The time difference between the first time a process goes into the running state and the arrival time of the process is called the response time of the process.

7) Gant Chart

The Gant chart is used to represent the currently executing process at every single unit of time. This time unit is the smallest unit of time in the processor.

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