Q 52,p3,d14.An operating system has 13 tape drives. There are three processes P1, P2 & P3. Maximum requirement of P1 is 11 tape drives, P2 is 5 tape drives and P3 is 8 tape drives. Currently, P1 is allocated 6 tape drives, P2 is allocated 3 tape drives and P3 is allocated 2 tape drives. Which of the following sequences represent a safe state ?

(A) P2 P1 P3 

(B) P2 P3 P1

(C) P1 P2 P3 

(D) P1 P3 P2

Answer A.

Explanation.

                                     

Allocated			max demand			max demand-allocation
P1	p2	p3	p1	p2	p3	p1	p2	p3
6	3	2	11	5	8	5	2	6

Total tapes 13. Allocated 11. Balance 2.

So first 2 units are given to p2. Then after completion p2 returns all 5.

Now 5 units are catered to p1. Now p1 returns 11 units.

Which can easily be given to p3.

Hence order is p2,p1,p3.

See banker's algo for detail.