Discuss the three techniques used for mapping blocks of memory into cache line
The three techniques used for mapping blocks of memory into cache lines are:
1. Direct Mapping:
In direct mapping, each block of memory is mapped to a specific cache line through a mathematical calculation. The mapping is done by dividing the main memory into equal-sized blocks and the cache into equal-sized lines. Each block is then mapped to a specific line using a modulus operation. For example, if there are 16 cache lines, the block at the memory address 'x' would be mapped to cache line (x modulo 16). This technique is simple to implement but may lead to frequent cache conflicts when multiple memory blocks are mapped to the same cache line.
2. Associative Mapping:
In associative mapping, each block of memory can be mapped to any cache line without any specific order. The memory blocks are stored in the cache along with tags that provide the memory block's actual address. When a memory block needs to be cached, the cache controller checks all the cache lines in parallel to find the one that matches the required memory block's tag. Associative mapping allows flexibility in mapping and reduces cache conflicts but requires more hardware complexity and has higher latency due to parallel searching.
3. Set-Associative Mapping:
Set-associative mapping combines the advantages of both direct mapping and associative mapping. The cache is divided into multiple sets, and each set contains a limited number of cache lines. Each memory block is mapped to a specific set using a mathematical calculation similar to direct mapping. Within each set, the memory block can be placed in any of the cache lines using associative mapping. The search for a specific memory block is limited to a specific set, reducing the search time compared to fully associative mapping. Set-associative mapping balances the trade-off between cache conflicts and hardware complexity. It provides better performance than direct mapping and faster searching than fully associative mapping.