ISRO | ISRO CS 2011 | Question 60

A total of 9 units of a resource type available, and given the safe state shown below, which of the following sequence will be a safe state?

Process   Used    Max
  P1        2      7
  P2        1      6
  P3        2      5
  P4        1      4

(A) (P4, P1, P3, P2)
(B) (P4, P2, P1, P3)
(C) (P4, P2, P3, P1)
(D) (P3, P1, P2, P4)


Answer: (D)

Explanation: Applying Banker’s Algorithm, Need matrix of the processes are:

Process   Used    Max    Need
  P1        2      7      5
  P2        1      6      5
  P3        2      5      3
  P4        1      4      3 

Currently Available resources = Available – Allocated resources = 9 – 6 = 3

If the request of P4 is granted first then it would release a maximum of 4 resources after its execution, and if P1 or P2 are allocated next then their requests can not be fulfilled as both of them require 5 resources each.
So, that eliminates Options (A), (B) and (C).

Option (D) is correct.

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