Locality of Reference - Defined (2 Marks)

Locality of reference is the empirical observation that memory references tend to cluster in a small region over a short time interval. It is the basis for cache and virtual memory.

1. Temporal Locality: If a memory location is referenced, it is likely to be referenced again soon. e.g. loops, reusable variables, stack. Keeping recently used blocks in cache yields hits.

2. Spatial Locality: If a location is referenced, nearby locations are likely to be referenced soon. e.g. sequential instruction fetch, arrays. Fetching a whole block/line exploits this.

3. Sequential Locality: Special case of spatial — ordered instruction execution.

Due to locality, 90/10 rule holds: 90% of time CPU accesses only 10% of address space, making cache hierarchy very effective.