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A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data from the main memory. [1] A cache is a smaller, faster memory, located closer to a processor core, which stores copies of the data from frequently used main memory locations.
Cache hierarchy, or multi-level cache, is a memory architecture that uses a hierarchy of memory stores based on varying access speeds to cache data. Highly requested data is cached in high-speed access memory stores, allowing swifter access by central processing unit (CPU) cores.
Level 1 (L1) Data cache – 128 KiB [citation needed] [original research] in size. Best access speed is around 700 GB/s [9] Level 2 (L2) Instruction and data (shared) – 1 MiB [citation needed] [original research] in size. Best access speed is around 200 GB/s [9] Level 3 (L3) Shared cache – 6 MiB [citation needed] [original research] in size.
Processor performance increase due to cache hierarchy depends on the number of accesses to the cache that satisfy block requests from the cache (cache hits) versus those that do not. Unsuccessful attempts to read or write data from the cache (cache misses) result in lower level or main memory access, which increases latency.
Diagram of a CPU memory cache operation. In computing, a cache (/ k æ ʃ / ⓘ KASH) [1] is a hardware or software component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewhere.
A victim cache is a small, typically fully associative cache placed in the refill path of a CPU cache. It stores all the blocks evicted from that level of cache and was originally proposed in 1990. In modern architectures, this function is typically performed by Level 3 or Level 4 caches.
Cache placement policies are policies that determine where a particular memory block can be placed when it goes into a CPU cache. A block of memory cannot necessarily be placed at an arbitrary location in the cache; it may be restricted to a particular cache line or a set of cache lines [1] by the cache's placement policy. [2] [3]
If all blocks in the higher level cache are also present in the lower level cache, then the lower level cache is said to be inclusive of the higher level cache. If the lower level cache contains only blocks that are not present in the higher level cache, then the lower level cache is said to be exclusive of the higher level cache. If the ...