UGC NET CSE | December 2008 | Part 2 | Question: 21

Question

N processes are waiting for $I/O$. A process spends a fraction $p$ of its time in $I/O$ wait state. The $CPU$ utilization is given by :

1. 1-p-N            
2. 1-pN             
3. pN                  
4. p-N

Answer 1

Ans is B

Let p=20% of time of process invest in i/o

N=1

Cpu utili.=1-pN=1-(.2)^1=.80=80%

N=2

Cpu utili.=1-(0.2)^2=1-.04=.96=96%

And so on..

So in multiprogramming environment if no. Of processes increases the CPU utili. Also increases

Answer 2

Ans: B CPU utilization = 1 - p ^n

ref: http://brahms.emu.edu.tr/filizbilen/OS/Lecture%20Notes-Chapter%202.pdf