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Resources » Articles/Knowledge Sharing » Computer & Technology »
Cache Memory
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Hello Friend,
Cache memory is one of the most important concept in modern hardware or computer field.
A Cache or Cache memory is an intermediate memory between two memories having large difference between their speed of operation. Cache memory is normally implemented between a hard disk and the RAM. It may also be inserted between CPU and RAM to gold the most frequently used data and instructions. Communicating with devices with a cache memory in between enhances the performance of a system significantly.
It is a common observation that at a particular time interval, references to memory tend to be confined within a few localized areas in memory. This phenomenon is known as locality of reference. Its illustration can be given by making use of control structure like 'loop'. Cache memories exploit this situation to enhance the overall performance.
Whenever a loop is executed in a program CPU executes the loop repeatedly, the same subroutine is called repeatedly. Thus loops and subroutines tend to localize the references to memory for fetching instructions. To a lesser degree, memory references to data also tends to be localized. Table lookup procedure repeatedly refers to that portion in memory, where the table is stored. Iterative procedures refer to common memory locations and array of numbers are confined within a local portion of memory. The result of these observations is locality of reference property.
The fundamental idea of cache organization is that by keeping the most frequently accessed instructions and data in via fast cache memory, the average memory access time will reach near to access time of cache.
Basic Operation : -
Whenever CPU needs to access the memory, cache is examined. If the word is found in the cache, it is read from the fast memory. If the word is not found in cache, main memory is accessed to read the word. A block of words just accessed by CPU is then transferred from main memory to cache memory.
Performance of Cache Memory : -
The performance of cache memory is frequently measurable in terms of a quality called Hit Ratio.
When the CPU refers to memory and finds the word in cache, it is said to produce a 'hit'. If the word is not found in cache it is called a 'miss'.
Hit ratio is a ratio of hits to misses. High hit ratio signified validity of "locality of reference". If the hit ratio is high enough then most times the CPU accesses the cache instead of main memory, the average access time is closer to access time of fast cache memory.
The characteristic of cache memory is that it is very fast. So very little or no time is wasted when searching for words in the cache. The transformation of data from main memory to cache memory is referred to as a mapping process.
These mapping processes will be discussed in next articles.
- Article by,
Sunil Saharan
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