# Job Scheduling Algorithms – Q&A

Question 1[20 marks]
One of the main purpose of the Operating System is to control the hardware and more specifically the CPU. The CPU performs all the jobs/processes requested by the different applications. A scheduler is a program of the Operating System that manages the amount of time that is allocated to each job that the CPU needs to process. To do so the scheduler keeps a list of all the jobs that needs to be processed. This is called the job queue. The scheduler also uses a scheduling algorithm to determine in which order these jobs will be processed and the amount of processing time to allocate to each job.

The main job scheduling algorithms are:
• FCFS: First Come First Served
• Round Robin
• Shortest Job First
• Shortest Remaining Time First
• Multilevel Feedback Queues
This question is based on the following job queue:

For each of the following scheduling algorithms:
1. Determine the order in which each job will be processed by the CPU (e.g. ABCD).
2. Estimate the completion time for each job in the queue.
Current time: 01:00 (mm:ss) – Round Robin Time Slice: 1s
FCFS: ……………
Job A: Completion time:
Job B: Completion time:
Job C: Completion time:
Job D: Completion time:

Round Robin: ……………
Job A: Completion time:
Job B: Completion time:
Job C: Completion time:
Job D: Completion time:

Shortest Job First: ……………
Job A: Completion time:
Job B: Completion time:
Job C: Completion time:
Job D: Completion time:

Shortest Remaining Time First: ……………
Job A: Completion time:
Job B: Completion time:
Job C: Completion time:
Job D: Completion time:

Question 2[4 marks]
Some job scheduling algorithms can potentially lead to starvation? Out of the four algorithms listed in question 1, what algorithms can potentially lead to starvation? Explain what would cause this?

#### Solution...

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