Types of Schedulers cont…

Types of Schedulers cont…

• Medium term Scheduler
• Is part of the swapping function i.e. it is in charge of handling the swapped out-processes
• It removes process from the memory e.g. suspended processes may be moved to the secondary storage (swapping) and make space for other processes
• It reduces the degree of multiprogramming

Scheduling Algorithms

Scheduling Criteria

• CPU Utilization – CPU is costly device, it must be kept as busy as possible
• Throughput – refers to the number of processes completed in unit time
• Turn around time – the time interval between the submission of the process and time of completion
• Waiting time – amount of time a process has been waiting in the ready queue
• Response time – time duration between the submission and first response

Scheduling Algorithms

• A major division among scheduling algorithms is whether they support pre-emptive or non-pre-emptive scheduling discipline:
• Pre-emptive scheduling
• A scheduler may pre-empt a low priority running process anytime when a high priority process enters into a ready state
• Pre-emptive scheduling is more useful in high priority process which requires immediate response e.g Real time system.
• Round Robin scheduling, priority based scheduling or event driven scheduling and SRT
• Non pre-emptive scheduling
• Once a process enters the running state, it cannot be pre-empted until it completes its allocated time
• Always processes a scheduled job to its completion.
• First come First Served (FCFS) and Shortest Job First (SJF)

Scheduling Algorithms

• First-Come First-Serve (FCFS)
• Shortest-Job First (SJF)
• Round Robin (RR)
• Shortest Remaining Time Next (SRTN)
• Priority Based Scheduling or Event Driven (ED) Scheduling
• Multilevel Queue Scheduling (Research)
• Multilevel Feedback Queue Scheduling (Research)