A system has a cache memory. However, the program running on the system…

1. Cache hit definition

   • Cache hit occurs when requested data is found in cache memory.

     Introduction to Memory Hierarchy

2. Cache miss definition

   • Cache miss occurs when requested data is not present in cache and must be fetched from main memory.

     Introduction to Memory Hierarchy

3. Given scenario

   • Memory accesses are random.

   • No data reuse.

   • No locality of reference.

4. Effect on cache hit ratio

   • Hit ratio becomes extremely low.

   • Almost every access becomes a cache miss.

5. Diagram of situation

Normal case

CPU → Cache → Main Memory
     (Hit)

Random access case

CPU → Cache → Miss → Main Memory

1. Effect on system performance

   • CPU must frequently wait for main memory.

   • Memory access time increases.

2. Effect on memory hierarchy

   • Cache becomes ineffective.

   • Hierarchy advantage reduces.

3. Example

Sequential access

A[0], A[1], A[2], A[3]

High spatial locality → high cache hits.

Random access

A[10], A[9000], A[120], A[55000]

No locality → cache misses.

1. Conclusion

   • Cache performance strongly depends on locality of reference.