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Assignment6Solution

Assignment6Solution - Department of Computer Science...

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Department of Computer Science University of Minnesota, Twin Cities CSci 5103 - Operating Systems -- Fall 2010 (Instructor: Tripathi) Assignment 6 Solution Posted on: November 16 12:30 pm Problem 1: (a) Memory access time when TLB hit = 20 + 100 = 120 Memory access time with TLB miss = 20 + 100 + 100 = 220 Effective memory access = 0.9 x 120 + 0.1 x 220 = 108 + 22 = 130 nano seconds (b) Let p denote the probability of page-fault on a memory access. Average memory access time = A = (1-p) 100 + p [ prob[modified page to be replaced]x10 7 + prob[unmodified page is replaced] x 5 x 10 6 ] It is required that A be less than equal to 200 nano seconds. Therefore 100 - 100 x p + p [ 0.8 x 10 7 + 0.2 x 5 x 10 6 ] < = 200 -100 x p + p [ 9 x 10 6 ] <= 100 Ignoring -100p term. P <= 100/ (9 x 10 6 ) = 1.11 x 10 -5 Problem 2: Answer: Assume that the page size is in terms of words, and an integer is stored in one word. I.e. a page can store 200 integers. Assume that the two dimensional array is stored in row major form. I.e. the array elements A[i][0], A[i][1]…,A[i][99] are stored in consecutive locations.
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