UGC NET CS 2016 July- paper-2
October 4, 2023Database-Management-System
October 4, 2023Operating-Systems
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Question 5
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Consider a fully associative cache with 8 cache blocks (numbered 0-7) and the following sequence of memory block requests:
4, 3, 25, 8, 19, 6, 25, 8, 16, 35, 45, 22, 8, 3, 16, 25, 7
If LRU replacement policy is used, which cache block will have memory block 7?
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4
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5
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6
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7
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Question 5 Explanation:
When 45 comes, the cache contents are:
4, 3, 25, 8, 19, 6, 16, 35
CPU array (first element being least recently used)
[4, 3, 19, 6, 25, 8, 16, 35]
So, 45 replaces 4.
45, 3, 25, 8, 19, 6, 16, 35 [3, 19, 6, 25, 8, 16, 35, 45]
Similarly, 22 replaces 3 to give,
45, 22, 25, 8, 19, 6, 16, 35 [19, 6, 25, 8, 16, 35, 45, 22]
8 hits in cache.
45, 22, 25, 8, 19, 6, 16, 35 [19, 6, 25, 16, 35, 45, 22, 8]
3 replaces 19,
45, 22, 25, 8, 3, 6, 16, 35 [6, 25, 16, 35, 45, 22, 8, 3]
16 and 25 hits in cache,
45, 22, 25, 8, 3, 6, 16, 35 [6, 35, 45, 22, 8, 3, 16, 25]
Finally, 7 replaces 6, which is in block 5.
4, 3, 25, 8, 19, 6, 16, 35
CPU array (first element being least recently used)
[4, 3, 19, 6, 25, 8, 16, 35]
So, 45 replaces 4.
45, 3, 25, 8, 19, 6, 16, 35 [3, 19, 6, 25, 8, 16, 35, 45]
Similarly, 22 replaces 3 to give,
45, 22, 25, 8, 19, 6, 16, 35 [19, 6, 25, 8, 16, 35, 45, 22]
8 hits in cache.
45, 22, 25, 8, 19, 6, 16, 35 [19, 6, 25, 16, 35, 45, 22, 8]
3 replaces 19,
45, 22, 25, 8, 3, 6, 16, 35 [6, 25, 16, 35, 45, 22, 8, 3]
16 and 25 hits in cache,
45, 22, 25, 8, 3, 6, 16, 35 [6, 35, 45, 22, 8, 3, 16, 25]
Finally, 7 replaces 6, which is in block 5.
Correct Answer: B
Question 5 Explanation:
When 45 comes, the cache contents are:
4, 3, 25, 8, 19, 6, 16, 35
CPU array (first element being least recently used)
[4, 3, 19, 6, 25, 8, 16, 35]
So, 45 replaces 4.
45, 3, 25, 8, 19, 6, 16, 35 [3, 19, 6, 25, 8, 16, 35, 45]
Similarly, 22 replaces 3 to give,
45, 22, 25, 8, 19, 6, 16, 35 [19, 6, 25, 8, 16, 35, 45, 22]
8 hits in cache.
45, 22, 25, 8, 19, 6, 16, 35 [19, 6, 25, 16, 35, 45, 22, 8]
3 replaces 19,
45, 22, 25, 8, 3, 6, 16, 35 [6, 25, 16, 35, 45, 22, 8, 3]
16 and 25 hits in cache,
45, 22, 25, 8, 3, 6, 16, 35 [6, 35, 45, 22, 8, 3, 16, 25]
Finally, 7 replaces 6, which is in block 5.
4, 3, 25, 8, 19, 6, 16, 35
CPU array (first element being least recently used)
[4, 3, 19, 6, 25, 8, 16, 35]
So, 45 replaces 4.
45, 3, 25, 8, 19, 6, 16, 35 [3, 19, 6, 25, 8, 16, 35, 45]
Similarly, 22 replaces 3 to give,
45, 22, 25, 8, 19, 6, 16, 35 [19, 6, 25, 8, 16, 35, 45, 22]
8 hits in cache.
45, 22, 25, 8, 19, 6, 16, 35 [19, 6, 25, 16, 35, 45, 22, 8]
3 replaces 19,
45, 22, 25, 8, 3, 6, 16, 35 [6, 25, 16, 35, 45, 22, 8, 3]
16 and 25 hits in cache,
45, 22, 25, 8, 3, 6, 16, 35 [6, 35, 45, 22, 8, 3, 16, 25]
Finally, 7 replaces 6, which is in block 5.
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