Cache Memory Overview

- Cache memory is a small and fast type of memory that is located close to the CPU.
- It is used to store frequently accessed data and instructions for faster access.
- Cache memory operates on the principle of locality of reference, which states that recently accessed data is likely to be accessed again in the near future.

Two-way Set-Associative Cache

- In a two-way set-associative cache, each block in main memory can be mapped to two cache blocks.
- The cache is divided into sets, and each set contains two blocks.
- The cache memory in this scenario consists of a total of four blocks, which means there are two sets.

LRU Replacement Scheme

- The least recently used (LRU) replacement scheme is used to decide which block to replace when a cache miss occurs.
- In this scheme, the block that has not been accessed for the longest time is chosen for replacement.

Cache Misses Calculation

We need to calculate the number of cache misses for the given sequence of block addresses: 8, 12, 0, 12, 8.

1. 8: Cache Miss (Block 8 is not present in the cache, so it is fetched from main memory and stored in the cache)
Cache State: {8, -}

2. 12: Cache Miss (Block 12 is not present in the cache, so it is fetched from main memory and stored in the cache)
Cache State: {8, 12}

3. 0: Cache Miss (Block 0 is not present in the cache, so it is fetched from main memory and stored in the cache)
Cache State: {0, 12}

4. 12: Cache Hit (Block 12 is already present in the cache)
Cache State: {0, 12}

5. 8: Cache Hit (Block 8 is already present in the cache)
Cache State: {0, 12}

The number of cache misses is equal to the number of times a block is not present in the cache and needs to be fetched from main memory. In this case, there are 3 cache misses.

Explanation
- Initially, the cache is empty, so the first three block addresses (8, 12, 0) result in cache misses.
- When block 12 is accessed again, it is already present in the cache, so it is a cache hit.
- Similarly, when block 8 is accessed again, it is also a cache hit.
- Therefore, the total number of cache misses for the given sequence is 3.

Final Answer
The number of cache misses for the given sequence of block addresses 8, 12, 0, 12, 8 is 3.