ITS A PPT

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CACHE MEMORY ORGANIZATION
AND DIFFERENT CACHE
MAPPING TECHNIQUES AND
TECHNIQUES TO REDUCE
CACHE MISS

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WHAT IS CACHE MEMORY ?
• Very high speed memory
• Used to reduce the average time to access data from the main memory
• Smaller and faster memory which stores copies of the data from frequently used
main memory locations
• Used to speed up and synchronizing with high speed CPU
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WHAT ARE THE LEVELS OF MEMORY ?
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• Level 1 or Register :
I. Data is stored and accepted and accepted that are immediately stored in CPU
ii. Most commonly used register is accumulator, address register etc.
• Level 2 or Cache Memory :
i. Fastest Memory which has faster access time
ii. Data temporarily stored for faster access
• Level 3 or main Memory :
i. Here computer works properly
ii. Small in size and once power is off, data is no longer stays in the memory
• Level 4 or Secondary Memory :
i. External type memory
ii. Not fast as main memory but data stays permanently in this memory

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WHAT IS CACHE MAPPING ?
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• A technique by which the contents of main memory are brought into
cache memory
WHAT ARE TH DIFFERENT TECHNIQUES OF CACHE MAPPING ?
• DIRECT MAPPING
• ASSOCIATIVE MAPPING
• SET ASSOCIATIVE MAPPING

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WHAT IS DIRECT MAPPING ?
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• We assign each memory block to a specific line in the cache
• The old block is trashed, when the line is previously taken by memory block and the
new block needs to be loaded
• An address is split into two parts i.e. index field and tag field
• It is directly proportional to hit ratio
• Each main memory address can be viewed as consisting of three
fields
• The least significant w bits identify a unique word or byte within a
block of main memory
• Remaining s bits specify one of the 2^s blocks of main memory
• There is also a field of r bits and this field identifies one of the 2^r
lines of the cache

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WHAT IS ASSOCIATIVE MAPPING ?
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• The associative memory is used to sore content and addresses of the memory
word
• Any block can go into any line in the cache
• The word bits are used to identify which word in the block is needed, but the tag becomes all
of the remaining bits
• This enables the placement of any word at any place in the cache
memory
• It is considered to be the fastest and the most flexible mapping form

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WHAT IS SET ASSOCIATIVE MAPPING ?
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• This form of mapping is an enhanced form of direct mapping where the drawbacks
of direct mapping are removed
• It addresses the problem of possible thrashing in direct mapping method
• Instead of having exactly one line that a block can map to the cache, we will group a few lines
together creating a set
• It allows that each word is present in the cache can have two or more
words in main memory for same index addresses
• It combines the best of direct and associative mapping techniques

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CACHE PERFORMANCE
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• When the processor needs to read or write a location in main memory, it first
checks for a corresponding entry in the cache
• If the processor finds that the memory location is in the cache, a cache hit has
occurred and data is read from cache
• If the processor does not find the memory location in the cache, a cache miss has
occurred
• For a cache miss, the cache allocates a new entry and copies in data from main memory
• The performance of cache memory is frequently measured in terms of a quantity called Hit Ratio.
Hit ratio = hit / (hit + miss) = no. of hits/total accesses

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WHAT IS CACHE MISS ?
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• It is an event which a system makes a request to retrieve data from a cache,
but the data is not present in the cache memory
• WHAT ARE THE DIFFERENT TECHNIQUES TO REDUCE CACHE MISS ?
• FIFO ALGORITHM
• OPTIMAL PAGE REPLACEMENT ALGORITHM
• LRU ALGORITHM

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FIFO ALGORITHM (FIRST IN FIRST OUT)
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Hit Ratio=(5/20*100)%=25%
Miss Ratio=(15/20*100)%=75%

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OPR ALGORIHM (OPTIMAL PAGE REPLACEMEMNT)
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Hit Ratio=(9/18*100)%= 50%
Miss Ratio=(9/18*100)=50%

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LRU ALGORITHM (LEAST RECENTLY USED)
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Hit Ratio=(8/20*100)%=40%
Miss Ratio= (12/20*100)%=60%

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THANK YOU
RITESH KUMAR SHAW-13000220104
AMBARISH ADAK-13000220105
ABHISEKH KUMAR GUPTA-13000320018