GATE | GATE CS Mock 2018 | Question 24

Consider 4-way set-associative cache memory has the following properties:

• Data words are 32 bits each
• A cache block will contain 2048 bits of data
• The address supplied from the CPU is 32 bits long
• There are 2048 blocks in the cache
• Addresses are to the word

Number of bits in tag?

(A) 17
(B) 15
(C) 16
(D) None of the above

Answer: (A)
Explanation: – There are still 6 bits in the offset; data is word addressed
Number of bits in index?
– We now need one less bit of index because we address to the set
→ 2^11 blocks / 2^2 blocks/set = 2^9 sets
→ (9 bits of index needed)
Number of bits in tag?
→ 32 – 6 – 9 = 17 bits.

So, option (A) is correct.
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