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Cache Memory  Presentation Transcript

1. Cache Memory

2. Contents:

1. Introduction

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.

3. Introduction

• 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

9. Mapping

• Mapping:- The transformation of data from main memory to cache memory is referred to as a mapping process

. • Types of mapping:-

1.Associative mapping

2.Direct mapping

3.Set-associative 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

Disadvantage:-

• Cache is more expensive than RAM.

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