1. Jazan University, Jazan KSA
Chapter 4
Lecture 10
Faheem
Lecturer, CNET Dept.,
Jazan University, Jazan KSA
Cache Memory

2. Cache Memory Mapping
Memory Mapping means, making connection or link between main memory with the cache memory.
Because there are fewer cache lines than main memory blocks, an algorithm is needed for mapping main memory blocks into cache lines. Further, a means is needed for determining which main memory block currently occupies a cache line. The choice of the mapping function dictates how the cache is organized.
There are two techniques used in memory mapping, direct and associative.
Book Page No 124

3. Direct Mapping
In direct mapping Each block of main memory maps into one unique line of the cache.
The above concept is clear from the diagram below.
Book Page No 126
Direct Mapping

4. Associated mapping The second type of mapping is associated mapping.
In associated mapping each block of main memory is associated to all line of cache memory.
The above concept is clear from the diagram below.
Book Page No 126
Associated Mapping

5. Replacement algorithms
Once the cache has been filled, when a new block is brought into the cache, one of the existing blocks must be replaced. For direct mapping, there is only one possible line for any particular block, and no choice is possible. For the associative techniques, a replacement algorithm is needed.
Book Page No 136

6. FIFO example First In First Out

7. LRU Least recently Used

8. Replacement algorithms
There are three replacement algorithm, MRU, LRU and FIFO, that is
Most recently used algorithm
Least recently used algorithm
First in first out
In direct mapping there is no choice, as each block only maps to one line so replace that line.
Book Page No 136

9. Thank you!!!
Chapter 4
Ends!!!