Cache Memory Unit

The cache memory unit is a small, fast memory that is used to store frequently accessed data and instructions. It acts as a buffer between the CPU and the main memory, providing faster access to data and reducing the average access time.

Set-Associative Cache

A set-associative cache is a type of cache organization that combines the benefits of direct-mapped and fully associative caches. In a set-associative cache, the cache is divided into multiple sets, and each set contains multiple cache lines. Each memory block can be mapped to any one of the cache lines within a set, based on a specific mapping function.

Capacity of Cache Memory Unit

In this question, we are given that the capacity of the cache memory unit is 256 KB. This means that the cache can store 256 kilobytes of data.

Number of Tag Bits

The number of tag bits determines the number of unique memory blocks that can be stored in the cache. In a 4-way set-associative cache, each set contains 4 cache lines. Therefore, the total number of cache lines in the cache is 4 times the number of sets.

Calculating Memory Size

To calculate the memory size, we need to determine the number of sets in the cache. Since the cache is 4-way set-associative, each set contains 4 cache lines. The total number of cache lines in the cache is given by the capacity of the cache divided by the size of each cache line.

Capacity of cache = 256 KB
Number of cache lines = Capacity of cache / Size of each cache line

Since the cache is 4-way set-associative, the number of sets in the cache is equal to the number of cache lines divided by 4.

Number of sets = Number of cache lines / 4

Finally, the memory size can be calculated by multiplying the number of sets by the size of each cache line.

Memory size = Number of sets * Size of each cache line

Applying the Calculation

In this question, we are given that the number of tag bits is 6. The size of each cache line can be calculated by subtracting the number of tag bits from the total number of bits in a cache line.

Size of each cache line = Total number of bits in a cache line - Number of tag bits

Since we are not given the total number of bits in a cache line, we cannot determine the size of each cache line. Therefore, it is not possible to calculate the memory size based on the given information.

Hence, the answer provided, '4', is incorrect as it does not consider the given information about the number of tag bits.