Operating Systems Questions and Answers updated daily – Computer Knowledge


Operating Systems Questions and Answers updated daily – Computer Knowledge



193 Operating Systems Questions and answers section with explanation for various online exam preparation, various interviews, Computer Knowledge Operating Systems online test. Operating Systems Questions with detailed description, explanation will help you to master the topic.

Operating Systems Questions

1. RAID level 0+1 is used because, RAID level 0 provides ______ whereas RAID level 1 provides ________.



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Correct Ans:performance, reliability
Explanation:


2. RAID level 5 is also known as :



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Correct Ans:block-interleaved distributed parity
Explanation:


3. RAID level 3 supports a lower number of I/Os per second, because _______________.



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Correct Ans:every disk has to participate in every I/O request
Explanation:


4. Which of the following algorithms tends to minimize the process flow time ?



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Correct Ans:Shortest Job First
Explanation:


5. There are 10 different processes running on a workstation. Idle processes are waiting for an input event in the input queue. Busy processes are scheduled with the Round-Robin timesharing method. Which out of the following quantum times is the best value for small response times, if the processes have a short runtime, e.g. less than 10ms ?



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Correct Ans:tQ = 15ms
Explanation:


6. The strategy of making processes that are logically runnable to be temporarily suspended is called :



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Correct Ans:Preemptive scheduling
Explanation:


7. The FIFO algorithm :



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Correct Ans:first executes the job that came in first in the queue
Explanation:


8. Consider a virtual memory system with FIFO page replacement policy: for an arbitrary page access pattern, increasing the number of page frames in the main memory will



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Correct Ans:sometimes increase the number of page faults
Explanation:
FIFO suffers from belady's anomaly, thus the number of page faults is increased though in general increases in number of page frames decreases the number of page faults.


9. Consider 3 CPU intensive processes, which require 10,20 and 30 time units and arrive at time 0,2 and 6 respectively. How many context switches are needed , if the operating system implements a shortest remaining time first scheduling algorithm? Do not count the context switches at time zero and at the end



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Correct Ans:2
Explanation:
P1 will start at 0 and will finish at 10, P2 will start at 10 and will finish at 30, P3 will start at 30 and will finish at 60. So there are only 2 context switches required at time unit 10 from P1 to P2, and at time unit 30 from P2 to P3


10. The data blocks of a very large file in the Unix file system are allocated using



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Correct Ans:an extension of indexed allocation
Explanation:
Indexed allocation is used for the efficient direct access good use of disk space. However, it cannon t allocated very large files . Thus, the data blocks of very large file in unix system are allocated using an extension of indexed allocation or EXT2 file system


11. A thread is usually defined as a light weight process because an operating system maintains smaller data structures for a thread than for a process. In relation to this, which of the following is true?



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Correct Ans:On per thread basis, the operating system maintains only cpu register state
Explanation:


12. The essential contents in each entry of a page table is/are



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Correct Ans:Page frame number
Explanation:


13. Consider an OS capable of loading and executing a single sequential user process at a time. The disk head scheduling algorithm used is FCFS. If FCFS is replaced by shortest seek time first (SSTF), claimed by the vendor to give 50% better benchmark results, what is the expected improvement in the IN/OUT performance of user programs?



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Correct Ans:0%
Explanation:
SSTF is optimal scheduling scheme for the access of file only. Therefore, the IN/OUT performance of the user program is determined by disk. So when FCFS is replaced by SSTF it improves only disk performance. This does not improve the entire IN/OUT performance . This implies improvement performance of user program is 0%


14. Which of the following statements are true?
I. Shortest remaining time first scheduling may cause starvation.
II. preemptive scheduling may cause starvation.
III. Round robin is better than FCFS in terms of response time.



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Correct Ans:I, II , III
Explanation:


15. Consider the following statements with respect to user level threads and kernel supported threads;1. Context switch is faster with kernal supported threads.
2. For user level threads, a system call can block the entire process
3. Kernel supported threads can be scheduled independently
4. User level threads are transparent to kernel.
Which of the above statements are true ?



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Correct Ans:2 and 3
Explanation:


16. Using a larger block size in a fixed block size file system leads to



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Correct Ans:poor disk throughput and poor disk space utilization
Explanation:
Throughput is the measure of total number of process completed per unit time. CPU utilization is referred to a process to keep CPU busy. Thus in case of large block size in fixed block size file system, CPU utilization is poorer and throughput is also decreased


17. Consider a set of n tasks with known runtimes r1,r2, .... rn to be run on a uniprocessor machine. Which of the following processor scheduling algorithms will result in the maximum throughput ?



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Correct Ans:shortest job first
Explanation:
If the number of processors are increased then amount of work done is increased and time is decreased. In case of uniprocessor first come first serve gives the maximum throughput but when the case of known run time is considered shortest job first gives best performance


18. List I contains some CPU scheduling algorithms and List II contains some applications. Match entries in List I to entries in List II using the codes given below the list

List I _______ List II
P) Gang scheduling _______ 1.Guaranteed scheduling
Q) Rate monotonic scheduling _______ 2. Real time scheduling
R) fair share scheduling _______ 3. Thread scheduling



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Correct Ans:P-3, Q-2, R-1
Explanation:


19. A system uses FIFO policy for page replacement. It has 4 pages frames with no pages loaded to begin with. The system first access 100 distinct pages in some order and then access the same 100 pages but now in reverse order. How many page faults will occur ?



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Correct Ans:196
Explanation:
100 pages are accessed in some order 1->100 , this will result in 100 page faults.When accessed in reverse order there won't be any fault for page number 100,99,98,97. Therefore for the remaining 96 access, 96 faults would occur. Total 196 page faults


20. In a system with 32 bit virtual addresses and 1 kb page size, use of one level page tables for virtual to physical address translation is not practical because



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Correct Ans:large memory overhead in maintaining page table
Explanation:
1 kb - 2^10 byte, virtual address = 32 bit therefore no. of pages - 2^21/2^10 = 222 bytes The required number of page is very large hence, it is not practical to implement as it will face issue of large memory overhead in the maintenance of page table



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