3. Systems Software GapFill

Scheduling is the means of assigning  jobsstorageCPU timememory to processes.  There are several algorithms by which scheduling is performed, and how a system schedules depends upon the specific nature of that system.   priority schedulingfixed-priority schedulingFirst-come, first-servedround robin simply takes the jobs in the order in which they arrive.  If, during execution, another job comes along,  its priority is examined and it might begin immediatelythe first process must then wait for the second to completeit is assigned to a different coreit must wait until the current job is complete.  The jobs themselves are stored in one or more data structures, specifically  queuestreesgraphsstacks.

Another algorithm is called  default schedulingpriority schedulinground robinpre-emptive scheduling, in which each job is assigned a  time sliceprocess control blocksegmentpage of equal size.  If that's enough for the job to complete, then it leaves the data structure.  If not, it waits its turn until it is allocated another one.  A  shortest job firstsmallest job firstsmallest time remainingshortest time remaining begins by examining each job in the data structure, and selecting the job predicted to have the  largest memory allocationlargest CPU burstsmallest memory allocationsmallest CPU burst.  This job is then executed  until interruptedfor a fixed amount of timeuntil it is completeunless a higher priority job is generated, at which point the algorithm repeats.  Then there's  smallest job firstshortest remaining timeshortest job firstsmallest time remaining, which is similar, but a job can be interrupted by a  lower priority jobnewer yet shorter jobhigher priority jobnewer, longer job.  These two approaches can both result in  overclocktime expiryprocess lockstarvation for longer jobs.

A  fixed-priority pre-emptive schedulermultilevel feedback queuenon-pre-emptive schedulervariable-priority pre-emptive scheduler combines one or more other scheduling algorithms in a single scheduling approach.  If the job is not completed during one pass, rather than being placed back in the same data structure to wait it can be moved to a different one with a different scheduling algorithm.