Scheduling and Gantt Charts

Question 1

Why multiprogramming

Answer 1

max CPU utilization

Question 2

Why CPU scheduling

Answer 2

implement multiprogramming

Question 3

CPU scheduler criteria

Answer 3

CPU utilization Throughput Turnaround

Question 4

Wait time

Answer 4

time spent in ready queue

Question 5

Turnaround time

Answer 5

sum of: wait to get to memory+time in ready Q + CPU time + I/O time

Question 6

response time

Answer 6

time from submission of request until 1st response produced

Question 7

scheduling algorithms

Answer 7

FCFS (FIFO), SJF, RR, priority (SJF is form of priority)

Question 8

burst time

Answer 8

burst in computers language is time slice allocated to CPU Alternate - CPU time for performing calculations CPU bound process might have a few long CPU bursts

Question 9

determine length of next CPU burst

Answer 9

t_n = actual length of nth CPU burst

T (tau)_n+1 = predicted value for next CPU burst

a(alpha): 0<=a<=1

Then T_n+1 = at_n + (1-a) T_n

need to decide assumptions for a

Question 10

RR

Answer 10

cpu executes p1 for time quantum, then goes to next process; p1 is back in ready queue at end (FIFO)

quantum must be large for context switch, otherwise overhead is too high

large quantum for RR is FIFO

Question 11

Gantt chart for RR

time quantum = 4

P1 burst = 24

P2 burst = 3

P3 burst = 3

Answer 11

p1 p2 p3 p1 p1 p1 p1

0-4 4-7 7-10 10-13 14-17 18-21 22-25 26-29