Question

Consider three processes (process id 0, 1, 2, respectively) with compute time bursts 2, 4, and 8 time units. All processes arrive at time zero. Consider the longest remaining time first (LRTF) scheduling algorithm. In LRTF ties are broken by giving priority to the process with the lowerst process id. The average turn around time is

• A. 14 units
• B. 15 units
• C. 13 units
• D. 16 units

Answer 1

The correct option is C 13 units

Process id	Arrival Time	CPU burst
$P_0$ $P_1$ $P_2$	0 0 0	2 4 8

The Gantt chart for LRTF CPU scheduling algorithm.

$P_0$

$P_1$

$P_2$

$P_2$

$P_2$

$P_2$

$P_2$

$P_1$

$P_2$

$P_1$

$P_2$

$P_0$

$P_1$

$P_2$

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Turn around time for $P_0$ = 12 - 0 = 12
Turn around time for $P_1$ = 13 - 0 = 13
Turn around time for $P_2$ = 14 - 0 = 14
Average Turn Around Time
$=\frac{39}{3}=13$