This document describes the Shortest Job First (SJF) CPU scheduling algorithm. SJF prioritizes processes in the ready queue based on the shortest estimated CPU burst time so that the process with the shortest burst time is selected first. SJF aims to minimize average waiting times and turnaround times. However, it requires accurate predictions of burst times and cannot always be implemented in practice due to lack of future knowledge.

2. SHORTEST JOB FIRST

3.  When the CPU is available, it is assigned to the process
that has the smallest CPU burst. Ready queue is treated
as a priority queue based on smallest CPU time
requirement
 Priorities are assigned in inverse order of time needed for
completion of the entire job
 If equal time of completion, then FCFS is used for
assigning priority.
 Dispatcher selects shortest job (1st in queue) and runs to
completion

4.  Gives minimum average waiting time for a given set of
processes.
 Minimizes average turnaround time.
 It cannot be implemented at the level of short term CPU
scheduling.
 Store estimated value in PCB for the current burst, and
compare with actual value.
 Exponential averaging is used to estimate the process’
burst duration.

5.  Minimizes average waiting time.
 Provably optimal with respect to average turnaround
time.
 Throughput is high.

6.  In general, cannot be implemented.
 Requires future knowledge
 In practice, can’t actually predict the length of next
burst
 Can lead to unfairness or starvation
 Doesn’t always minimize average turnaround
time
 Elapsed time (i.e., execution-completed-time)
must be recorded, it results an additional
overhead on the processor.

7.  Criteria- Burst time
 Mode:- Non-Preemptive
Process No. Arrival Time Burst Time
1 1 7
2 2 5
3 3 1
4 4 2
5 5 8

8. Process No. Arrival Time Burst Time
1 1 7
2 2 5
3 3 1
4 4 2
5 5 8
Gantt Chart:-
0 1 8
P1
9
P3 P4
11
P2
16
P5
24