Popularly known as Johnson’s Algorithm, this sequencing algorithm for sequencing jobs through two machines was developed by Johnson. In this algorithm, the number of jobs (n) needs to be processed through its number of machines- M1 and M2. Since the operation time of M1 and M2 or the number of jobs is known, one needs to find a sequence that lessens this total time required to complete these jobs.

Assumptions of sequencing algorithm

Johnson’s algorithm on sequencing jobs is based on a number of assumptions. These presumptions are as follows-

• Various jobs arrive at the same static arrival pattern and they do not have any priority for completing the job.
• M1 and M2 are the only two machines and all jobs are being processed on both of these machines.

Steps involved in sequencing algorithm

Step-1: The operation time for each task should be listed down on M1 and M2.

Step-2: Choose the lowest processing or operation time from the list made in the previous step.

Step-3: Base your shortest processing time as per its sequence. For instance, if the lowest operation time is on M1, one needs to place its related task first in the sequence. However, if the minimum operation time is on M2, then the parallel job should be placed last in the sequence. In case of a tie in the operation time, it can be divided randomly.

Step-4: Do away with those tasks which have been sequenced already in step-3.

Step-5: Until you get all your jobs sequenced, keep on repeating the above step-2 and 3.

To have a better understanding of Johnson’s algorithm, it is better if students practice some sums on the same. This will give them necessary command which is required while dealing with this chapter in financial accounting.  