Cache
Mapping Technique
•Cache
is small, fast and expensive
memory.
•This
is also use for reducing
access time.
•Cache
is more closer to CPU than main memory.
•Cache is use to store
addresses.
•There
are three ways for mapping cache memory.
1.Direct
mapping
2.Fully
Associative mapping
3.Set-Associative
mapping
•These
method are use for assigning
addresses to cache locations.
1.Direct
mapping
•Direct mapping is the easiest.
•It is often use for instruction cache.
•In direct mapping no search is needed.
•But in this method the cache memory is not fully utilized.
•No replacement technique is required in this method of cache mapping.
•In this method only one tag compare is require per access.
•All words stored in cache must have different indices.
2. Fully Associative mapping
•In this type of mapping the tag memory is searched in parallel (Associative) hence it is called Associative mapping.
•In this method cache
utilization is very high as compare to other two technique.
•In this method main
memory divided into two groups lower
order bits
for location of a word in block and higher
order bits
for blocks.
•It is
expensive to implement because of cache searching.
•As much comparators as number of tags is required means large number of comparators is required.
•The internal
logic compare the incoming address with all the
stored addresses.
3. Set-Associative mapping
•Set-Associative
mapping have good
performance but it is complex.
•Set-Associative
mapping is the combination
of both direct mapping and fully associative mapping.
•In
this method the cache is divided
into sets.
•So
the search is performed over a cache
set in parallel.
•Set-Associative
mapping is use in microprocessors.
•It
allows limited number of blocks with same
index and different
tags.
•The incoming tag is compared with all
tags of selected sets with the help of comparator.
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