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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.
The most efficient caching algorithm would be to discard information which would not be needed for the longest time; this is known as Bélády's optimal algorithm, optimal replacement policy, or the clairvoyant algorithm. Since it is generally impossible to predict how far in the future information will be needed, this is unfeasible in practice.
The merit of inclusive policy is that, in parallel systems with per-processor private cache if there is a cache miss other peer caches are checked for the block. If the lower level cache is inclusive of the higher level cache and it is a miss in the lower level cache, then the higher level cache need not be searched.
The placement policy decides where in the cache a copy of a particular entry of main memory will go. If the placement policy is free to choose any entry in the cache to hold the copy, the cache is called fully associative. At the other extreme, if each entry in the main memory can go in just one place in the cache, the cache is direct-mapped.
The exclusive (E) state in MESI protocol implies that the cache block is valid, clean (same value as in the main memory) and cached only in one cache whereas the owned (O) state in MOSI protocol implies that the cache block is valid, potentially dirty, writable and could be present in more than one cache (all caches have the same value).
The third involved a video "impersonating the FBI and a United States government agency" with a purported statement that schools should suspend activities until Nov. 11.
Jun. 3—CONCORD — House and Senate negotiators made progress Monday, but there remained a sticking point over legislation to reduce the number of at-risk children placed in out-of-state treatment.
This policy ensures that the data is stored safely as it is written throughout the hierarchy. However, in the case of the write back policy, the changed cache block will be updated in the lower-level hierarchy only when the cache block is evicted. A "dirty bit" is attached to each cache block and set whenever the cache block is modified. [27]