Question

Consider a direct mapped cache of size 16 KB with block size 256 bytes. The size of the main memory is 128 KB. Find- 1. Number of bits in tag is :

Answer 1

The correct answer to find the number of bits in the tag for a direct mapped cache is to subtract the number of cache index bits from the number of main memory block bits, which yields 3 bits in this scenario.

Step-by-step explanation:

The correct answer is option 4. To calculate the number of bits in the tag for a direct mapped cache, we need to consider several factors: the size of the main memory, the size of the cache, and the block size. First, we calculate the number of blocks in the cache and main memory:

• Cache blocks = Cache size / Block size = 16KB / 256B = 64 blocks
• Main memory blocks = Main memory size / Block size = 128KB / 256B = 512 blocks

Then, we find out how many bits are needed to identify each block in the cache and main memory. Since there are 64 cache blocks, we need 6 bits for the cache (2^6=64). For the main memory, which has 512 blocks, we need 9 bits (2^9=512).

To find the tag size, we subtract the number of cache index bits from the number of main memory block bits: tag bits = main memory block bits - cache index bits = 9 bits - 6 bits = 3 bits.