Sage-Tips

What are the advantages of set associative cache memory?

Advantages of Set-Associative mapping Set-Associative cache memory has highest hit-ratio compared two previous two cache memory discussed above. Thus its performance is considerably better.

What is a set associative cache?

Set Associative Cache • Set associative caches are a. compromise between fully associative caches and direct-mapped caches. In a set associative cache, there are a fixed number of locations (called a set) that a given address may be stored in. The number of locations in each set is the associative of the cache.

What is a disadvantage of a fully associative cache?

2) Fully-Associative Cache – a memory block can map to any cache line. Advantage: Flexibility on what’s in the cache. Disadvantage: Complex circuit to compare all tags of the cache with the tag in the target address. Therefore, they are expensive and slower so use only for small caches (say 8-64 lines)

Why do you think virtual memory is not implemented like a fully associative cache?

Fully associative had the lowest miss rates, but was the most expensive, so it was never used. However, with virtual memory, the cost of a miss is so high that it doesn’t matter if fully associative takes longer, even if we can’t do the searching in parallel as we can in hardware.

Why is set associative cache organization better than direct mapping and fully associative mapping?

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.

What is advantage of fully associative mapping over direct mapping?

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.

Which cache is a fully associative cache?

Parallel hardware and parallel software At one extreme is a fully associative cache, in which a new line can be placed at any location in the cache. At the other extreme is a direct mapped cache, in which each cache line has a unique location in the cache to which it will be assigned.

How does fully associative cache work?

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.

How does a fully associative cache work?

Which cache miss does not affect fully associative caches?

Conflict misses occur high in direct mapped cache, medium in set associative cache, and zero in associative mapped cache.

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

Which mapping technique is best?

Set associative cache mapping combines the best of direct and associative cache mapping techniques. Usually, the cache memory can store a reasonable number of blocks at any given time, but this number is small compared to the total number of blocks in the main memory.

What is a fully associative cache?

Fully Associative Cache employs fully associative cache mapping technique. Fully Associative Mapping is a cache mapping technique that allows to map a block of main memory to any freely available cache line.

What is an n-way set associative cache?

An N-way set associative cache reduces conflicts by providing N blocks in each set where data mapping to that set might be found. Each memory address still maps to a specific set, but it can map to any one of the N blocks in the set.

What is the difference between a direct-mapped and associative cache?

Unlike a direct-mapped cache, they still require multiple tags be checked for every access. However, the number of checks to perform is fixed and doesn’t become prohibitive for larger caches: a 4-way set associative cache only requires 4 tags to be checked. A 16-way associative cache only requires 16 tag checks per access.

How do you increase the set associativity of a cache?

One method used by hardware designers to increase the set associativity of a cache includes a content addressable memory (CAM). A CAM uses a set of comparators to compare the input tag address with a cache-tag stored in each valid cache line. A CAM works in the opposite way a RAM works.