define Shortest-Job-First (SJF) Scheduling ?, Basic Computer Science

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• It is also known as Shortest-Process-Next (SPN).
• Shortest-Job-First (SJF) is a non-preemptive order in which waiting job (or process) with the smallest predictable run-time-to-completion is run next. In other language, when CPU is available, it is allotted to the process that has smallest next CPU burst.
• The SJF scheduling is mainly suitable for batch jobs for which the run times are known in advance. Since the SJF scheduling algorithm gives the minimum average time for a given set of processes, it is almost certainly optimal.
• The SJF algorithm helps short jobs (or processors) at the cost of longer ones.
• The understandable problem with SJF scheme is that it requires precise acquaintance of how long a job or process will run, and this information is not generally available.
• In the production environment where the same jobs run frequently, it may be possible to provide reasonable estimate of run time, based on the past presentation of the process. But in the development environment users not often know how their program will execute.
• The best SJF algorithm can do is to rely on user approximation of run times.
• Like FCFS, SJF is non preemptive therefore, it is not helpful in timesharing environment in which reasonable answer time must be sure.

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