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GATE | GATE-CS-2006 | Question 74

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Consider two cache organizations: The first one is 32 KB 2-way set associative with 32-byte block size. The second one is of the same size but direct mapped. The size of an address is 32 bits in both cases. A 2-to-1 multiplexer has a latency of 0.6 ns while a kbit comparator has a latency of k/10 ns. The hit latency of the set associative organization is h1 while that of the direct mapped one is h2. The value of h1 is:

(A)

2.4 ns

(B)

2.3 ns

(C)

1.8 ns

(D)

1.7 ns



Answer: (A)

Explanation:

Cache size = 32 KB = 32 * 210 bytes Cache block size = 32 bytes Number of blocks = 2 
Total combinations are : = cache size / (Number of blocks * block size) = 32 * 210 / (2 * 32) = 512 = 29 
Therefore, number of index bits = 9 
Since, cache block size is 32 bytes i.e. 25 bytes. Number of offset bits = 5 
So, number of tag bits = 32 – 9 – 5 = 18 
Hit latency (h1) = 0.6 + (18 / 10) ns = 2.4 ns 
 
Thus, option (A) is correct. 


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Last Updated : 19 Nov, 2018
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