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## Operating system mcqs semaphores

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Question 1 |

What are the two kinds of semaphores?

mutex & counting | |

binary & counting | |

counting & decimal | |

decimal & binary |

Question 2 |

The program follows to use a shared binary semaphore T. Process A int Y; A1: Y = X*2; A2: X = Y; signal(T); Process B int Z; B1: wait(T); B2: Z = X+1; X = Z; T is set to 0 before either process begins execution and, as before, X is set to 5. Now, how many different values of X are possible after both processes finish executing?

one | |

two | |

three | |

four |

Question 2 Explanation:

The semaphore T ensures that all the statements from A finish execution before B begins. So now there is only one way in which statements from A and B can be interleaved: A1 A2 B1 B2: X = 11.

Question 3 |

At a particular time of computation the value of a counting semaphore is 7.Then 20 P operations and 15 V operations were completed on this semaphore. The resulting value of the semaphore is? (GATE 1987)

42 | |

2 | |

7 | |

12 |

Question 3 Explanation:

P represents Wait and V represents Signal. P operation will decrease the value by 1 every time and V operation will increase the value by 1 every time.

Question 4 |

The following pair of processes share a common variable X. Process A int Y; A1: Y = X*2; A2: X = Y; Process B int Z; B1: Z = X+1; B2: X = Z; X is set to 5 before either process begins execution. As usual, statements within a process are executed sequentially, but statements in process A may execute in any order with respect to statements in process B. How many different values of X are possible after both processes finish executing?

two | |

three | |

four | |

eight |

Question 4 Explanation:

Here are the possible ways in which statements from A and B can be interleaved. A1 A2 B1 B2: X = 11 A1 B1 A2 B2: X = 6 A1 B1 B2 A2: X = 10 B1 A1 B2 A2: X = 10 B1 A1 A2 B2: X = 6 B1 B2 A1 A2: X = 12.

Question 5 |

Spinlocks are intended to provide ..... only.

Mutual Exclusion | |

Bounded Waiting | |

Aging | |

Progress |

There are 5 questions to complete.