Os Exam

Question 5

Acomputer system has four frames and uses six reference bits to implement and aging (additional-Reference-bits) algorithm.At first clock tick, the Reference bits for pages 0 through 3 are1,0,1, and 1 respectivety . At the next clock tick, the bits are 0011. Values at subsequent ticks are 1001,0110,1100,0001.After the last tick,What is the value of the Reference byte for all four pages (you have just to fill the table below)?

Page Number | Tick 1 | Tick 2 | Tick 3 | Tick 4 | Tick 5 | Tick 6 |

0 | 100000 | | | | | |

1 | 000000 | | | | | |

2 | 100000 | | | | | |

3 | 100000 | | | | | |

2- consider two processes , p1 and p2 where p1=50, t1=25 ,p2=75,and t2=30.

a) Can these two processes be scheduled using rate monotonic scheduling ?Illustrate your answer using a Gantt chart .

b) Illustrate scheduling of these two processes using earlist-deadline-frist(EDF) scheduling .

Question 4

1-Consider the following snap short of a system:

| Allocation | Max | Available |

| A B C D | A B C D | A B C D |

P0 | 0 0 1 2 | 0 0 1 2 | 1 5 2 0 |

P1 | 1 0 0 0 | 1 7 5 0 | |

P2 | 1 3 5 4 | 2 3 5 6 | |

P3 | 0 6 3 2 | 0 6 5 2 | |

P4 | 0 0 1 4 | 0 6 5 6 | |

Answer the following questions using the banker’s algorithm:

a- What is thet content of the matrix Need?

b-Is the system in a safe state ?Justify your answer.

c- If a request from process p1 arrives for (0,4,2,0) can the request be granted immediately?

2-give two advantages and two disadvantages of using may-to-one mapping ( in comparison may-to-many mapping ).

Question 3:

Consider a file currently consisting of 50 blocks of information .Assume that the file control block (and index block, in the case of indexed allocation ) is already in memory . calculate the number of disk I/O operation required for contiguous, linked, and indexed allocation strategies to make the following changes...