Consider a 4-way set associative cache consisting of 128 lines with a line…
2007
Consider a 4-way set associative cache consisting of 128 lines with a line size of 64 words. The CPU generates a 20-bit address of a word in main memory. The number of bits in the TAG, LINE and WORD fields arerespectively:
- A.
9,6,5
- B.
7, 7, 6
- C.
7, 5, 8
- D.
9, 5, 6
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Correct answer: D
Final answer: TAG = 9, LINE = 5, WORD = 6
Key steps:
Compute the word (offset) field: line size = 64 words → word bits = log2(64) = 6.
Compute the number of sets and the index (line) field: total lines = 128 and associativity = 4 → sets = 128 / 4 = 32 → index bits = log2(32) = 5.
Compute the tag field: address width = 20 bits → tag bits = 20 - (index bits + word bits) = 20 - (5 + 6) = 9.
Therefore the fields are TAG = 9 bits, LINE (index) = 5 bits, WORD (offset) = 6 bits.
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