Q. At a particular time of computation, the value of a counting semaphore is 10. Then 12 P operations and “x” V operations were performed on this semaphore. If the final value of semaphore is 7, x will be:

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Q. In a multi-user operating system, 30 requests are made to use a particular resource per hour, on an average. The probability that no requests are made in 40 minutes, when arrival pattern is a poisson distribution, is ...............

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Q. Normally user programs are prevented from handling I/O directly by I/O instructions in them. For CPUs having explicit I/O instructions, such I/O protection is ensured by having the I/O instructions privileged. In a CPU with memory mapped I/O, there is no explicit I/O instruction. Which one of the following is true for a CPU with memory mapped I/O?

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Q. Which of the following statements are true?

(a) External Fragmentation exists when there is enough total memory space to satisfy a request but the available space is contiguous.
(b) Memory Fragmentation can be internal as well as external.
(c) One solution to external Fragmentation is compaction.

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Q. Page information in memory is also called as Page Table. The essential contents in each entry of a page table is/are ....................

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Q. Consider a virtual page reference string 1, 2, 3, 2, 4, 2, 5, 2, 3, 4. Suppose LRU page replacement algorithm is implemented with 3 page frames in main memory. Then the number of page faults are .................

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Q. In which of the following scheduling criteria, context switching will never take place?

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Q. In Distributed system, the capacity of a system to adapt the increased service load is called .................

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Q. In .................... disk scheduling algorithm, the disk head moves from one end to other end of the disk, serving the requests along the way. When the head reaches the other end, it immediately returns to the beginning of the disk without serving any requests on the return trip.

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Q. Suppose there are six files F1, F2, F3, F4, F5, F6 with corresponding sizes 150 KB, 225KB, 75 KB, 60 KB, 275 KB and 65 KB respectively. The files are to be stored on a sequential device in such a way that optimizes access time. In what order should the files be stored?

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Q. Which module gives control of the CPU to the process selected by the short - term scheduler?

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Q. Two atomic operations permissible on Semaphores are .................. and ...............

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Q. Consider the following four schedules due to three transactions (indicated by the subscript) using read and write on a data item X, denoted by r(X) and w(X) respectively. Which one of them is conflict serializable?

S1 : r1(X); r2(X); w1(X); r3(X); w2(X)
S2 : r2(X); r1(X); w2(X); r3(X); w1(X)
S3 : r3(X); r2(X); r1(X); w2(X); w1(X)
S4 : r2(X); w2(X); r3(X); r1(X); w1(X)

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Q. Suppose a database schedule S involves transactions T1, T2, .............,Tn. Consider the precedence graph of S with vertices representing the transactions and edges representing the conflicts. If S is serializable, which one of the following orderings of the vertices of the precedence graph is guaranteed to yield a serial schedule?

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Q. Consider the following four processes with the arrival time and length of CPU burst given in milliseconds :

Process Arrival Time Burst Time
P1 0 8
P2 1 4
P3 2 9
P4 3 5

The average waiting time for preemptive SJF scheduling algorithm is .................

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Q. Consider a virtual page reference string 7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0, 1. Suppose a demand paged virtual memory system running on a computer system such that the main memory has 3 page frames. Then ................. page replacement algorithm has minimum number of page faults.

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Q. User level threads are threads that are visible to the programmer and are unknown to the kernel. The operating system kernel supports and manages kernel level threads. Three different types of models relate user and kernel level threads.

Which of the following statements is/are true?
(a) (i) The Many - to - one model maps many user threads to one kernel thread
(ii) The one - to - one model maps one user thread to one kernel thread
(iii) The many - to - many model maps many user threads to smaller or equal kernel threads

(b) (i) Many - to - one model maps many kernel threads to one user thread
(ii) One - to - one model maps one kernel thread to one user thread
(iii) Many - to - many model maps many kernel threads to smaller or equal user threads

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Q. Consider a disk queue with requests for I/O to blocks on cylinders 98, 183, 37, 122, 14, 124, 65, 67. Suppose SSTF disk scheduling algorithm implemented to meet the requests then the total number of head movements are ................... if the disk head is initially at 53.

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Q. The Bounded buffer problem is also known as ..................

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