Operating Systems · topic
Scheduling criteria and the metrics read off a Gantt chart (completion, turnaround, waiting, response), then FCFS, SJF, SRTF, round robin, priority with aging, multilevel and feedback queues and HRRN, with tie and arrival conventions and context-switch overhead.
When several processes are ready and there is one CPU, the short-term scheduler decides which runs next. The decision is made over and over, every few milliseconds, so the policy shapes how long jobs take, how responsive the system feels and whether some process can be postponed forever.
Interactive systems care about response time: a user who presses a key wants a reaction now, not after a long batch job finishes. Round robin (RR) achieves this by time slicing. Every ready process gets the CPU for at most one time quantum q, then goes to the back of the queue.
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