Given n processes with their burst times, the task is to find average waiting time and average turn around time using FCFS scheduling algorithm.
First in, first out (FIFO), also known as first come, first served (FCFS), is the simplest scheduling algorithm. FIFO simply queues processes in the order that they arrive in the ready queue.
In this, the process that comes first will be executed first and next process starts only after the previous gets fully executed.
Here we are considering that arrival time for all processes is 0.
How to compute below times in Round Robin using a program?
- Completion Time: Time at which process completes its execution.
- Turn Around Time: Time Difference between completion time and arrival time. Turn Around Time = Completion Time – Arrival Time
- Waiting Time(W.T): Time Difference between turn around time and burst time.
Waiting Time = Turn Around Time – Burst Time
In this post, we have assumed arrival times as 0, so turn around and completion times are same.
1- Input the processes along with their burst time (bt). 2- Find waiting time (wt) for all processes. 3- As first process that comes need not to wait so waiting time for process 1 will be 0 i.e. wt = 0. 4- Find waiting time for all other processes i.e. for process i -> wt[i] = bt[i-1] + wt[i-1] . 5- Find turnaround time = waiting_time + burst_time for all processes. 6- Find average waiting time = total_waiting_time / no_of_processes. 7- Similarly, find average turnaround time = total_turn_around_time / no_of_processes.
# Python3 program for implementation
# of FCFS scheduling
# Function to find the waiting
# time for all processes
def findWaitingTime(processes, n,
# waiting time for
# first process is 0
wt = 0
# calculating waiting time
for i in range(1, n ):
wt[i] = bt[i – 1] + wt[i – 1]
# Function to calculate turn
# around time
def findTurnAroundTime(processes, n,
bt, wt, tat):
# calculating turnaround
# time by adding bt[i] + wt[i]
for i in range(n):
tat[i] = bt[i] + wt[i]
# Function to calculate
# average time
def findavgTime( processes, n, bt):
wt =  * n
tat =  * n
total_wt = 0
total_tat = 0
# Function to find waiting
# time of all processes
findWaitingTime(processes, n, bt, wt)
# Function to find turn around
# time for all processes
bt, wt, tat)
# Display processes along
# with all details
print( “Processes Burst time ” +
” Waiting time ” +
” Turn around time”)
# Calculate total waiting time
# and total turn around time
for i in range(n):
total_wt = total_wt + wt[i]
total_tat = total_tat + tat[i]
print(” ” + str(i + 1) + “\t\t” +
str(bt[i]) + “\t ” +
str(wt[i]) + “\t\t ” +
print( “Average waiting time = “+
str(total_wt / n))
print(“Average turn around time = “+
str(total_tat / n))
# Driver code
if __name__ ==”__main__”:
# process id’s
processes = [ 1, 2, 3]
n = len(processes)
# Burst time of all processes
burst_time = [10, 5, 8]
findavgTime(processes, n, burst_time)
# This code is contributed
# by ChitraNayal
Processes Burst time Waiting time Turn around time 1 10 0 10 2 5 10 15 3 8 15 23 Average waiting time = 8.33333 Average turn around time = 16
- Average Waiting Time is not optimal
- Cannot utilize resources in parallel : Results in Convoy effect (Consider a situation when many IO bound processes are there and one CPU bound process. The IO bound processes have to wait for CPU bound process when CPU bound process acquires CPU. The IO bound process could have better taken CPU for some time, then used IO devices).
- Program for FCFS Scheduling | Set 2 (Processes with different arrival times)
- Program for Priority Scheduling | Set 1
- Program for Shortest Job First (or SJF) scheduling | Set 1 (Non- preemptive)
- Program for Preemptive Priority CPU Scheduling
- Program for Shortest Job First (SJF) scheduling | Set 2 (Preemptive)
- Program for Round Robin scheduling | Set 1
- Program for SSTF disk scheduling algorithm
- Weighted Job Scheduling | Set 2 (Using LIS)
- Weighted Job Scheduling
- Assembly Line Scheduling | DP-34
- Weighted Job Scheduling in O(n Log n) time
- Disk Scheduling Algorithms
- Job Scheduling with two jobs allowed at a time
- Operating Systems | CPU Scheduling | Question 7
- Operating Systems | CPU Scheduling | Question 6
In Set-2 we will be discussing the processes with different arrival time.
This article is contributed by Sahil Chhabra (akku). If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to email@example.com. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.