What is fully associative cache?

A fully associative cache ▪ A fully associative cache permits data to be stored in any cache block, instead of forcing each memory address into one particular block. — When data is fetched from memory, it can be placed in any unused block of the cache.

What is fully associative mapping?

Fully Associative Mapping refers to a technique of cache mapping that allows mapping of the main memory block to a freely available cache line. Also, a fully associative cache would permit the storage of data in any cache block. There would be no forcing of every memory address into a single particular block.

What is a 4 way set associative cache?

4-Way Set Associative. Fully Associative. No index is needed, since a cache block can go anywhere in the cache. Every tag must be compared when finding a block in the cache, but block placement is very flexible! A cache block can only go in one spot in the cache.

How many blocks are in a fully associative cache?

A memory address can map to a block in any of these ways. A fully associative cache is another name for a B-way set associative cache with one set. Figure 8.11 shows the SRAM array of a fully associative cache with eight blocks.

Why is fully associative cache better?

Full associative mapping has much less potential for collisions between blocks trying to occupy the cache. That is, two or more main memory blocks may have to fit into the same cache block with direct mapping, but could go into different cache blocks with a full (or set) associative mapping.

What is the disadvantage of a fully associative cache?

Explanation: The major disadvantage of the fully associative cache is the amount of hardware needed for the comparison increases in proportion to the cache size and hence, limits the fully associative cache.

How many sets are in a 4 way associative cache?

Associativity = 4-way associative. Width of offset = Log2(32) = 5. Number of cache lines = 1000 KB/32 = 32 K. Number of sets = 32K/4(4 way associative) = 8K, hence the size of SET address in bits = Log2(8K) = 13.

Can a fully associative cache have conflict misses?

Conflict misses are misses that would not occur if the cache were fully associative with LRU replacement. The second to last 0 is a capacity miss because even if the cache were fully associative with LRU cache, it would still cause a miss because 4,1,2,3 are accessed before last 0.

Is fully associative cache the best?

A fully associative cache is specified as a cache of size N blocks. Each block can map to any portion of memory. Fully associative caches are then the most flexible, because they give the replacement policy much more flexibility (has more blocks to choose from).

What is the main reason why set associative caches are used rather than fully associative caches?

The set-associative cache generally provides higher hit rates than the direct-mapped cache because conflicts between a small set of locations can be resolved within the cache.