سياسات الاستبدال وتحديد الموقع

Problems of cache design!
It should be clear that as more requests for items that do not exist in the cache (cache miss) occur, more blocks would have to be brought to the cache. This should raise (يثير) two basic questions:

first : Where to place an incoming main memory block in the cache?
Second: In the case where the cache is totally filled, which cache block should the incoming main memory block replace?
In other words, the designer faces two problems must be taken into consideration:
Placement of incoming blocks and Replacement of existing blocks are performed according.

Replacement Techniques
We discuss three algorithms that are used to deal with miss case when the cache is full:-
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A) Random Selection
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It is done based on the output of the random number generator at the time of replacement. The generator produce a number between 0 and (N - 1) where N is no. of blocks in cache. This technique is simple and does not require much additional overhead. However, its main shortcoming is that it does not take locality into consideration. Random techniques have been found effective enough such that they have been first used by Intel in its iAPX microprocessor series.