6. Associative and Multi-level Caches
The chapter discusses cache memory and how its organization affects performance, particularly focusing on associative and multi-level caches. It highlights the differences between direct-mapped, fully associative, and set-associative caching strategies, explaining their respective strengths and weaknesses in terms of cache miss rates. Furthermore, the chapter describes the importance of a block replacement policy for effective cache management.
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What we have learnt
- Cache memories can reduce misses through flexible block placement strategies.
- Fully associative caches allow any block to map to any line, while direct-mapped caches have strict mapping rules.
- The choice of cache organization affects performance and the overall hardware cost.
Key Concepts
- -- Cache Miss
- A failure to find a requested block of data in the cache, necessitating a fetch from slower main memory.
- -- Associativity
- The number of locations in cache where a given memory block can be placed, affecting flexibility and miss rates.
- -- Block Replacement Policy
- The strategy used to determine which block to evict from cache when new data is brought in, often determined by least recently used (LRU) or random schemes.
- -- DirectMapped Cache
- A cache where each block maps to exactly one specific location, which can lead to more conflicts and higher miss rates.
- -- SetAssociative Cache
- A hybrid approach where a block of memory can be placed in any of a set of locations, allowing for greater flexibility than direct-mapped caches.
- -- Fully Associative Cache
- The most flexible caching scheme where any block can be placed in any line in the cache, potentially minimizing miss rates but increasing complexity.
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