A multi-user, multi-processing operating system cannot be implemented on hardware that does not support:

Four jobs are waiting to be run. Their expected run times are $$6, 3, 5$$ and $$x$$. $${\rm I}$$n what order should they be run to minimize the average response time?

Four jobs to be executed on a single processor system arrive at time $${0^ + }$$ in the order $$A, B, C, D.$$ their burst $$CPU$$ time requirements are $$4, 1, 8, 1$$ time units respectively. The completion time of A under round robin scheduling with time slice of one time units.

The sequence $$.........$$ is an optimal non-preemptive scheduling sequence for the following jobs which leaves the $$CPU$$ idle for $$..........$$ Unit (s) of time