Answer:
- $876\;\text{sec}$
- $360\;\text{msec}$
- $348\;\text{msec}$
Explanation:
The order for FCFS:
$20\rightarrow10\rightarrow22\rightarrow20\rightarrow2\rightarrow40\rightarrow6\rightarrow38$
$\therefore$Distance $=10+12+2+18+38+34+32 = 146 \;\text{cylinders}$
$\therefore $Time $=146\times 6 = 876\;\text{sec}$
The order for CCN(SSTF):
$20\rightarrow20\rightarrow22\rightarrow10\rightarrow6\rightarrow2\rightarrow38\rightarrow40$
$\therefore $Distance$=0+2+12+4+4+36+2 = 60\;\text{cylinders}$
$\therefore $Time$=60\times 6 = 360 \;\text{msec}$
The order for Elevator(SCAN):
$20\rightarrow20\rightarrow22\rightarrow38\rightarrow40\rightarrow10\rightarrow6\rightarrow2$
$\therefore $Distance: $=0+2+16+2+30+4+4 = 58 \;\text{cylinders}$
$\therefore$ Time $=58\times6 = 348\;\text{msec}$