Cache Memory Presentation Transcript
1. Cache Memory
2. Cache memory in system
3. Features of cache
4. Basic operation
5. Performance of cache 6. Address relation between main and cache memory
7. Mappings – Associative mapping – Direct mapping – Set-associative mapping.
8. Writing into cache
9. Cache initialization
10. Advantages and Disadvantages of cache.
• Cache memory is extremely fast memory that is built into a computer’s CPU, or located on a separate chip.
• The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed.
• It is work on the principle Locality of reference.
4. Cache memory in system
5. Features of cache
• The access time is faster than main memory.
• The cache is placed on the top in the memory hierarchy.
• The cache organization is concerned with memory write requests.
• The cache is initialized when the main memory is loaded with a complete set of programs.
• Cache built into the CPU itself is referred to as Level 1 (L1) cache.
• Cache that resides on a separate chip is called Level 2 (L2). Eg:SRAM
6. Basic operation
7. Performance of cache
• The performance of cache memory is measured by Hit Ratio
. • When the CPU refers to memory and finds the word in cache,it counts as hit.If the word is not found then it counts as miss.
• Then we calculate Hit Ratio :-This ratio verifies the validity of the locality of references property.
• Hit Ratio=(total hit)/(total CPU references to memory) • Hit Ratio=(total hit)/(total hit +total miss).
• Hit Ratio of 0.9 and higher have been reported.
8. Address relation between main and cache memory
• Mapping:- The transformation of data from main memory to cache memory is referred to as a mapping process
. • Types of mapping:-
10. Associative mapping
11 Direct mapping
12. Set-associative mapping
13. Writing into Cache
• Two ways:
1. Write-through:-In this method we update main memory with every write operation.
The main memory contains same data as the cache.
2. Write-back:-In this method only the cache location is updated during a write operation.
14. Cache initialization
• The cache is initialized when the main memory is loaded with a complete set of programs from auxiliary memory.
• After cache initialization the cache is considered to be empty,and a valid bit is included with each word in cache.
• The cache is initialized by clearing all the valid bits to 0.
• The valid bit is set to 1 the first time any words is loaded and it still set until cache is again initialized.
15. Advantages and Disadvantages of cache Advantages:-
• It is the fastest memory in the system
. • cache is so effective in system performance
• The CPU does not have to use the motherboard’s system bus for data transfer.
• The CPU can process data much faster by avoiding the bottleneck created by the system bus
• programs can operate more quickly and efficiently
• Cache is more expensive than RAM.