CPU scheduling decisions take place under one of four conditions: When a process switches from the running state to the waiting state, such as for an I/O request or invocation of the wait( ) system call.
First come, first served (FCFS) is an operating system process scheduling algorithm and a network routing management mechanism that automatically executes queued requests and processes by the order of their arrival.
Preemptive scheduling: The preemptive scheduling is prioritized. The highest priority process should always be the process that is currently utilized. Non-Preemptive scheduling: When a process enters the state of running, the state of that process is not deleted from the scheduler until it finishes its service time.
Preemptive: This type of scheduling may preempt the central processing unit (CPU) in the case the priority of the freshly arrived process being greater than those of the existing processes. Non-preemptive: This type of scheduling algorithm simply places the new process at the top of the ready queue.
Round Robin is the preemptive process scheduling algorithm. Each process is provided a fix time to execute, it is called a quantum. Once a process is executed for a given time period, it is preempted and other process executes for a given time period.
Definition - What does Shortest Job First (SJF) mean? Shortest job first is a scheduling algorithm in which the process with the smallest execution time is selected for execution next. Shortest job first can be either preemptive or non-preemptive.
Shortest remaining time scheduling is the preemptive counter part of SJF and is useful in time sharing system. In SRT, process with the smallest estimated run time to completion is run next, in SJF once a job begin executing, it runs to completion.
Maximum throughput scheduling may be tempting in this context, especially in simulations where throughput of various schemes are compared. However, maximum throughput scheduling is normally not desirable, and channel-dependent scheduling should be used with care, as we will see below.