The number of bits in the tag field of an address is (A) 11 (B) 14 (C) 16 (D) 27

Question

A computer has a 256 KByte, 4-way set associative, write back data cache with block size of 32 Bytes. The processor sends 32 bit addresses to the cache controller. Each cache tag directory entry contains, in addition to address tag, 2 valid bits, 1 modified bit and 1 replacement bit.

The number of bits in the tag field of an address is 

(A) 11 

(B) 14 

(C) 16 

(D) 27

Answer 1

 (C) 16

Number of blocks = \(\frac{256KB}{32Bytes}\) = \(\frac{2^{18}}{2^5}\) = 2¹³blocks

As it is 4- way set associative, number of sets = \(\frac{2^{13}}{2^2}=2^{11}\)