Explain any three policies for process scheduling that uses resource consumption information.

All three policies for process scheduling are explained below in brief:

1. First-come First-served (FCFS) (FIFO)

- Jobs are scheduled in order of coming

- Nonpreemptive

• Problem:

- Average waiting time can be huge if small jobs wait behind long ones

- May cause poor overlap of I/O and CPU and convoy consequences

2. Shortest Job First (SJF)

- Select the job with the shortest next CPU burst

-For minimizing average waiting time provably optimal

• Problem:

- Not possible knowing the length of the next CPU burst

3. Round Robin (RR)

- Frequently used for timesharing

- Ready queue is function as a circular queue (FIFO)

- Each process is specified a time slice termed as a quantum

- This is run for the quantum or till it blocks

- RR allocates the CPU uniformly or fairly across each participant. If average queue length is n, all participants get 1/n

- Since the time quantum grows, RR becomes FCFS

- Smaller quanta are usually desirable, since they improve response time

• Problem:

- Context-switch over-head of frequent context-switch