os08-final - Operating System Final Exam for 2008 Fall...

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Operating System Final Exam. for 2008 Fall Semester Date: 01-14-2009, Time: 09:10 a.m.- 10:40 a.m. Name: Student ID: Dept: There are 9 problems in this examination with the indicated points of each (sub)problem. The total points fo this exam. is 110. Please do all of them. 1. [Basic Concepts](30%) These are 10(a-j) true or false problems. If your answer is false please give the true statement with respect to the original false one. (a) (3%) [Dynamic Loading vs. Dynamic Linking] With dynamic loading, a routine is not loaded until it is called. All routines are kept on disk in a relocatable load format. With dynamic linking, a stub is included in the image for each library-routine reference. Dy- namic loading requires special support from the operating system but dynamic linking generally does not require help from the operating system. (b) (3%) [Memory Fragmentation] Contiguous memory allocation scheme suffers from internal fragmentation as address spaces allocated contigu- ously and holes develop as old processes dies and new processes are ini- tiated. But pure segmentation suffers from external fragmentation as a segment of a process is laid out contiguously in physical memory and fragmentation would occur as segments of dead processes are replaced by segments of new processes.
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2 (c) (3%) [Belady’s Anomaly] The Belady’s anomaly cannot be shown in the stack page-replacement algorithms. Like optimal page replacement, LRU page replacement done not suffer from Belady’s anomaly because they all belong to a class of stack page-replacement algorithms. (d) (3%) [Working-Set Model] The working-set model is based on the assumption of locality. The most important property of the working set is its size. If we compute the working-set size, WSS i , for each process in the system, we can then consider D = WSS i , where D is the total demand for frames. Thus process i needs WSS i frames. If the total demand D is less than the total number of available frames m , e.g. ( D < m ), thrashing will occur, because some processes will not have enough frames.
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