This document discusses First Come First Serve (FCFS) scheduling algorithm. It explains that FCFS is a non-preemptive scheduling technique that processes jobs in the order of their arrival without interrupting running jobs. The document then provides examples of applying FCFS scheduling with and without consideration for processes' arrival times. It shows the Gantt charts generated from scheduling processes in different orders based on their arrival times and calculates turnaround times and waiting times.

1. Operating
System
CSE-3107
MD.SHAHRIAR PERVEZ EFTI
Student of CSE Department

2. First Come First Serve (FCFS)
First Come First Serve (FCFS) is a type of scheduling algorithm used
by operating systems.
2
FCFS is a non-preemptive scheduling algorithm

3. Non-preemptive
Non-preemptive scheduling is a CPU scheduling technique that holds a process
until it finishes or is pushed into a waiting state. No process is interrupted until it
completes.
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4. 4
FCFS With Arrival Time
Here, the Arrival Time of P3 is 0.So, P3 Arrive first.
Process AT BT CT TAT WT
P1
P2
P3
P4
P5
3
4
0
3
5
1
5
2
7
5

5. 5
P3
GanttChart:
0 2
Here, Due to the arrival time of p3 being 0, P3 sits first in the ganttchart and runs for
2s
Process AT BT CT TAT WT
P1
P2
P3
P4
P5
3
4
0
3
5
1
5
2
7
5

6. 6
P3 P1
GanttChart:
0 2 3
Now we will check if any processor
has arrived in 2 units of time .
After checking we see that no
process arrived in 2 units of time but
again 2 new processes P1 and P4
both arrive in 3 units of time.
Here, According to the sequence P1
is located before P4 .So before P1
arrives. And from 2 units of time to 3
unit of time the CPU will be idle.
Proces
s
AT BT CT TAT WT
P1
P2
P3
P4
P5
3
4
0
3
5
1
5
2
7
5

7. 7
7
Proces
s
AT BT CT TAT WT
P1
P2
P3
P4
P5
3
4
0
3
5
1
5
2
7
5
P3 P1 P4 P2 P5
GanttChart:
0 2 3 4 11 16 21
Now we will check if any processor
has arrived in 3 units of time .
After checking we see that P1 & P4
arrive in 3 units of time. But P1
arrive first and then P4 because of
their sequence of order whose
finishing time are 4 & 11.
Then we will check in same way.
After checking we see that P2 will sit
and then P5 will sit whose finishing
time are 16 & 21.

8. 8
Proces
s
AT BT CT TAT WT
P1
P2
P3
P4
P5
3
4
0
3
5
1
5
2
7
5
4
6
2
11
21
1
12
2
8
16
0
7
0
1
11
P3 P1 P4 P2 P5
GanttChart:
0 2 3 4 11 16 21
Completion time(CT) of Process is
collected from Gantt chart.
Trun around time is calculated by
these TAT=CT-AT.
Waiting time is calculated by these
WT=TAT-BT.

9. 9
FCFS Without Arrival Time
Here, Process will sits Gantt chart in according to their order.
Process BT CT TAT WT
P1
P2
P3
P4
P5
3
4
0
3
5
1
5
2
7
5

10. P1 P2 P3 P4 P5
0 1 6 8 15 20
Process BT CT TAT WT
P1
P2
P3
P4
P5
3
4
0
3
5
1
6
8
15
20
1
6
8
15
20
0
1
6
8
15
TAT=CT Due to
absence of AT
WT=TAT-BT.
10

11. Any
questions?
11

12. Thanks You!
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