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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 hits are the number of accesses to the cache that actually find that data in the cache, and cache misses are those accesses that don't find the block in the cache. These cache hits and misses contribute to the term average access time (AAT) also known as AMAT ( average memory access time ), which, as the name suggests, is the average time ...
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.
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 cache has two primary figures of merit: latency and hit ratio. A number of secondary factors also affect cache performance. [1] The hit ratio of a cache describes how often a searched-for item is found. More efficient replacement policies track more usage information to improve the hit rate for a given cache size.
Consider the case when L2 is inclusive of L1. Suppose there is a processor read request for block X. If the block is found in L1 cache, then the data is read from L1 cache and returned to the processor. If the block is not found in the L1 cache, but present in the L2 cache, then the cache block is fetched from the L2 cache and placed in L1.
It is different than the external memory model because cache-oblivious algorithms do not know the block size or the cache size. In particular, the cache-oblivious model is an abstract machine (i.e., a theoretical model of computation). It is similar to the RAM machine model which replaces the Turing machine's infinite tape with an infinite array.
In computing (specifically data transmission and data storage), a block, [1] sometimes called a physical record, is a sequence of bytes or bits, usually containing some whole number of records, having a maximum length; a block size. [2] Data thus structured are said to be blocked.